Chevy S10 - GMC S15 and Sonoma Radiator and Cooling Issues

sn4ck0sn4ck0 Member Posts: 8
Recently replaced the head, and while doing so, I had broke off the Plug in for the Coolant Temp Switch below the Thermostat, so, I didn't pay it any mind drove it, then a bit later, I broke down and replaced it, (temp gauge before didn't work until I replaced it) so now it works, after ignition and idling about 5-10 mins or so, it would readout 260^, when stated with the new Switch it would idle at 1k RPM, before without it it would idle at about 1400 RPM then Idle down to 1k RPM (guessing when the Thermo opened etc), anyways, I've replaced the thermostat, and thinking it might be the h20 Pump I took that off, and it's in good order, and even reverse flushed the Radiator.

Any Ideas on what else to do, or what the problem might be?


  • gonogogonogo Member Posts: 879
    Did you bleed all the air out? Will it overheat going down the road, or just when idling.

    You have a clutch fan on a 95 I assume, will it roar when it gets hot, it should.

    260 F is getting ready to boil over. What temp is the coolant in the radiator, I use a candy thermometer, wife doesn't know.
  • sn4ck0sn4ck0 Member Posts: 8
    I'm Not Quite for sure what you mean bleed the air out, as in out of the Radiator?

    Overheat doing both, and yes it'll engage not all the time, but I checked the spin of it, and it's seemingly stout, and no cracks.

    With the New Temp Switch, it's like there is no water moving anywhere, remains stagnant, and is cool/cold (top and bottom hoses are cool as well) with the Switch unplugged water is exceedingly warm, and I can view h20 moving. top hose it hot to touch.

    Note, there is a metal tubing going from below the thermostat housing toward the back of the engine, (assume to the Heater core) and it is HOT with both scenarios.

    Another thing I tried, was the have the heater on with the new switch, and it seemed like it would take longer to Overheat, but in both cases the Heater was ...doing it's job, nice and hot :).
  • gonogogonogo Member Posts: 879
    Puzzled, you say with the temp sensor unplugged, it makes a difference?
    I reread your posts, it did not appear to overheat until you got the gauge working. I don't think your gauge is accurate, check actual water temp .
  • sn4ck0sn4ck0 Member Posts: 8
    Strange I know,

    I did so, had to take off the Thermostat housing, and saw that it was hot, steam, extremely hot to touch.

    The problem is, with the thing plugged in, seems like the Thermo is not opening, so I removed the thermostat, and replaced it all together, and it seemed to have worked.

    and if that is indeed the case, (Bad thermo) that would make two in a row.

    One thing I saw, after taking the housing off, was one time there wasn't enough h20 to fill up to the sensor. (I think that is what you refered to as Airlocked, so I made adjustments and tried to fix that (Jacked up one side, and started with the heater on)

    has to be one of two three things

    Thermostat (again)
    Waterpump (doesn't seem likely, as it was pumping with out the thermo in)
    Sensor, that's the only thing I haven't replaced (after the initial replacement)

    Any Ideas on what to do/check?
  • rrt1441rrt1441 Member Posts: 2
    My 95 S10 engine light comes on and temperature on gauge is higher than normal. Light comes on after driving a few miles and engine is hot. Have not noticed if the fan comes on. Could this be a sensor, or thermostat?
  • gonogogonogo Member Posts: 879
    I still think it is a gauge problem, not the right sensor, try a Delco sensor. Or gauge wiring problem, or bad gauge.
  • jae5jae5 Member Posts: 1,206
    When you replaced the original thermostat did you install the new one in the same position as the old. On the 4.3s you have to have the thermostat clocked in the right position or you can have issues. You can also check thermostat operation really easy by placing the thermostat in a pot and bring the water to a boil and see when it opens (should be 195 as stated).

    Are you using dex-cool (orange) coolant or the regular green? If using Dex-Cool you have to use a flushing agent / kit to get all of the old crap out; if not you can run into the problems you're having as well.

    You still may be having an air problem. You definitely have to have the heater on, blower on high, when your topping off or you can get air trapped in the system. You can do the initial system fill with everything shut off but after that you need to have the engine running and the the heater on to get the air out to finish topping it off. And what do you mean you jacked up one side? Did you jack up the truck so that water / coolant would fill up to the sensor? And you are using water / coolant right, not straight water.

    As stated the sensor may be out of spec, not sending out the right signal or is the wrong one. But it wouldn't cause an "real" overheating issue as it shouldn't be blocking a main coolant passage.
  • cachevycachevy Member Posts: 1
    I just purchased a 2000 S-10, with a 4.3 V-6, I am being told by my mechanic that this product eats up the inside of engine & I already have a intake leak.
    Also that it is better to flush coolant out & replace with green anti-freeze.
    Any suggestions out there? :confuse:
    I did not expect this appox. $700 repair B-4 I've driven truck more than 200 miles.
    Any thing else to look for? :surprise:
  • littleoscolittleosco Member Posts: 11
    We have the same vehicle, same engine. We were told that the Dex Cool needs to be replaced fairly often or it gets thick and gums up your engine. Come to think of it, we've only changed it a couple times and it's probably due again. I've not heard of replacing it with regular anti freeze but just being aware that the Dex Cool can cause these problems.
  • lovethytrucklovethytruck Member Posts: 1
    My cooling fan isn't kicking on. The temp. guage seems to be working fine since it reads normal while the vehicle is moving. I tried free-spinning the fan blades with the engine off and there is plenty of resistance. I checked all the fuses, both under the hood and in the dashboard, and they are all okay. Not quite sure where to go from here. No other symptoms other than overheating at idle or after the engine has been shutoff. Any suggestions would be appreciated.
  • cmac8874cmac8874 Member Posts: 2
    My 1995 S-10 is leaking from the backside of the engine. I can't see any visual signs on the top, but underneath a steady stream is coming down between the starter and oil pan. I was wondering if there are freeze plugs back there that I can't see. The oil is clear of water, so I'm hoping it's not a cracked head. Just wondering if anyone else has had this problem.
  • jpfjpf Member Posts: 496
    What size engine is it?
  • cmac8874cmac8874 Member Posts: 2
    4.3 vortec
  • jpfjpf Member Posts: 496
    I had a 2000 S10 extended cab with the same engime. It had a leak from the intake manifold gasket. The truck never overheated but did lose coolant. Cost like $300 to $400 to fix if I recall correctly. Good luck.
  • sniperwafflessniperwaffles Member Posts: 2
    I've got some issues with my sonoma its a 2000 with 185,000 miles. its been in one crash(not my fault). had some body work and new chip(registers E-brake and ABS gauge). But now im getting overheating issues within the first couple minutes of driving. spikes to (260). I thought it was leaking and replaced the hose/valve running rome radiator to engine. today when i turned it off i smelt anti-freeze and heard a sizzling sound? any thoughts? :mad:
  • sniperwafflessniperwaffles Member Posts: 2
    hey i have a 2000 GMC sonoma and everytime I drive it. The temperature guage is spiking up into the 260 range? once I stopped and popped the hood i could smell anti-freeze and heard a sizzling sound. As if something is leaking and the engine is so hot it fry's the liquid. I've replaced the hose going from radiator to engine. Also checked the valve that connects the hose to the engine. that fixed the problem for a while now the problem has returned. (2nd time with the sizzling-1st without) Sny suggestions?? :mad:
  • freddy0872freddy0872 Member Posts: 6
    I have a 1998 Chevy S-10 with a 2.2L Engine. There is a steel pipe on the top of the engine towards the drivers side. It is mounted down with one bolt on the back side and held into the thermostat housing on the front. It also contains the Coolant Temperature Sensor right before the thermostat housing. And on the back side of the pipe there is a rubber hose that has engine labeled on it. This steel pipe is leaking and i need to buy a new one to replace it. What exactly is the name for this pipe so the guys at the auto parts store can look it up for me. Any help is greatly appreciated.
  • berto01berto01 Member Posts: 1
    This sounds identical to the problems I have had with my 2000 s10. The dexcool stuff is terrible and GM recently settled a class action lawsuit giving most truck owners 50 to 300 hundred for repairs. Did you fix your intake leak or?? Just curious as I now have one as well.
  • gonogogonogo Member Posts: 879
    That leak happens now and then, not yet on my 99, but only 55K. Just buy a new pipe and housing assy, it should be available after market.
  • bcrawf53bcrawf53 Member Posts: 4
    I flushed the cooling system and replaced thermostate on my 2002 GMC Sonoma with79,000 miles on it.
    I've had nothing but probems after that. Service engine light came on, did diagnostic - water temp below engine temp. Replaced temprature sending unit. Same thing? I have to drive 10 miles before engine reaches operating temp?
  • gonogogonogo Member Posts: 879
    Bad thermostat.
  • bcrawf53bcrawf53 Member Posts: 4
    I'll try it and let you know!
  • peter931peter931 Member Posts: 13
    After [email protected] radiator and water pump on GMC Sonoma 4.3L coolant is leaking to oil pan. Truck is not smoking and compression is good on each cylinder. What could be the problem?
  • bcrawf53bcrawf53 Member Posts: 4
    I change the thermostate and it is working fine so far. I'll have to wait for cooler weather for a real test. It seems to work better when the outside temp is higher than +40 degrees. Fuel mileage is up to thank goodness.
  • bcrawf53bcrawf53 Member Posts: 4
    4.3L 's have an issue with intake manifold's leaking. I had the same problem on my 94 GMC Safari. Changing the gasket took care of the problem!
  • peter931peter931 Member Posts: 13
    It is a 3.0L SOHC engine. No engine interference. After R&R timnig belt , engine is not running on 6 cylinders. All the marks on cams and cranc are in position , distributor rotor is on #1 . Piston #1 is in the TDC . I am in dead end.
    Any one know where could be the problem?
  • firstof3cooksfirstof3cooks Member Posts: 1
    I have a '95 GMC Sonoma 2.2L that's getting hot. The temp gauge only goes to about 210. But smoke is coming into the car through the heater. I thought it was the thermostat because I smell that radiator smell, but obviously that's not it. Any suggestions?
  • gonogogonogo Member Posts: 879
    Your heater core is leaking, not an easy job.
  • the_big_althe_big_al Member Posts: 1,079
    Truck: 2001 Ex-cab 2wd s-10

    Drivetrain: 4.3 V6 with Auto trans

    I seem to have a coolant leak somewheres. It comes from the back of the motor. When the coolant level gets low enough the leak seems to stop, as well as the heater. When I fill the coolant back up, I can park the truck and after a few minutes (a run into the gas station to pay is long enough), I come back and it is dripping from the back of the motor at a pretty good rate.

    When I run the heater, I dont get any odd smells into the cabin, but the heater will quit working once the coolant level gets low enough. I also do not have oil int he coolant or coolant in the oil. No smoking out the back of the tail pipe. The truck runs just fine. The only time it goes wonky is when the coolant level gets low. When the coolant is full, the temp gauge runs just below halfway (210 I think) and stays there. It also gets there quite quickly and always has. I know there is a couple of different places the leak could be, but I was wondering if there is a most likely culprit.
  • gonogogonogo Member Posts: 879
    Low coolant will effect heater operation. Seeing you have a V6, I would suspect the infamous intake manifold coolant leak, most times they will leak external. That's good news for you, get it repaired ASAP.
  • the_big_althe_big_al Member Posts: 1,079
    although I am not looking for a step by step process (I'm pretty good at reading a chilton :D), but what is the basic process to do this??
  • gonogogonogo Member Posts: 879
    Get a book, easiest way to have complete information.
    First you need to look closer, prove it is the intake gasket, don't want to tear it all apart for nothing.
  • jetjunkyjetjunky Member Posts: 1
    I have a 2002 S-10, 4.3, A/T. I just change the thermostat to a 195 deg. The operating temp now stays at 210 deg.( mid range on the gage ). My question is will this be detrimental to the life of the engine, will I see any difference in mpg, any adverse effects in warmer outside temps? I live in Phx. Ariz. so the temps can get quite hot in the summer months. What is the recommended operating water temp? Thanks for any help.
  • the_big_althe_big_al Member Posts: 1,079
    As far as I can remember, my S-10, an '01 4.3 A/T has always read right at the 210 (midway) point once warmed up. In the summer it has been dead on mid-point and in winter it reads just a hair below. My truck also spent several summers in Phoenix and I had no problems. I have the standard 180 degree (I think it's 180) T-stat. I have changed it once and I stuck with an OEM one.

    You won't see any damage if the temps stay at 210. What you do need to worry about is that in the summer, you might see the temp range in the higher side rather than the low side because of the 195 degree t-stat. That is something that I would be careful of. Instead of operating between 100 and 210, you are now operating between 210 and 260, which can get dangerous on hot days. Especially in rush hour traffic traveling at only 10 MPH.

    In my opinion, I would switch back to the standard factory t-stat. Is there a reason you went to the 195 degree one? People make all sorts of claims pertaining to running one, but I haven't tested it to be sure and so I don't know. They all sound like hocus pocus to me.
  • tork49tork49 Member Posts: 4
    You could be 180 degrees off? At # 1 cylinder both exhaust and intake should be loose if you want TDC ( top dead center)? This means that. both intake and exhaust valves should be loose upon inspection or both are closed. This is a common mistake and don't feel bad about it! When you turn the crank, the rotor should be pointing towards #1 on the cap or distributor? Wires for #1 should be located at front not back of engine. Hopefully, this will want you!
  • gary_ogary_o Member Posts: 1
    I have a 2003 Sonoma 4x4 ZR2 with 71,000+. The engine temperature heats to 190 and then Fluctuates between 190 and 210. When it get to 210 the heat inside the cab blows cold air. When it returns to 190 the heat returns. I have had the thermostat replaced at 55,000 and the heater control panel inside the cab was changed out due to transmission valve vacuum failure. Truck starts normal and idles normal. After about 25 minutes of running the engine stops the temperature swings. Any ideas? About every 9000 miles I have to add antifreeze.
  • the_big_althe_big_al Member Posts: 1,079
    (This is an old post, but maybe you are still searching for a solution?)

    Here are some things to check... You have a coolant leak somewhere. More than likely it is the intake gasket (see my next post on this very issue). The reason you have no heat, even at 210 is because you have low coolant. You do not have enough coolant to get into the heater core. Do you notice that after you add coolant that your heater works properly? This was happening to me. I would have a temp reading of 190-210 and no heat. I would then add coolant and I would have heat after a few minutes. I was losing coolant at the intake. This is common on these motors to do that (so I have heard)... With the truck running and with a full coolant level, check for drips under the truck. If you have an external leak, you might get lucky and it will be bad enough to see. If you have an external leak you are also lucky in that you won't have water in your oil. If you have an internal leak, check your oil. You should see a white milky film in the oil. You can also check the oil by parking the truck overnight, crawling under and cracking the oil plug. Since water is heavier than oil, it will sink to the lowest part of the pan (where the plug is) and be the first thing to come out when you pull off the plug. You won't have to pull the plug off all the way, just enough so that if there is water in the pan, it will start to come out. If there is water in the pan, more than likely you have an intake manifold that is leaking...

    Now see my next post on that...
  • the_big_althe_big_al Member Posts: 1,079
    A while back I posted about a coolant leak. I finally found and fixed it... (ya ya it took a while. Thanks gonogo for pointing me in the right direction).

    It was indeed the intake manifold. Boy oh boy was it bad. Okay - here's the short story. A while back, several months ago in fact I realized I had a coolant leak. My heater would quit working and so after doing research (on here mostly) I found it to be low coolant. I wasn't losing coolant rapidly enough for me to do much about it, plus funds were a bit short and it also wasn't or didn't seem to be an internal leak so I didn't worry TOO much about it. I should have and so I know I played a bit of a gamble here. I rolled the dice and luckily I seem to have come out okay, but not counting my chips yet. Anyway...

    Fast forward to a couple weeks ago. I am headed to work and my temperature shoots towards hot. I pull over and realized that I am REALLY low on coolant. Like almost out. That'd odd because I had just filled it. Literally like not even a week earlier. I was able to limp home after some cooling off and getting water into it, but while the truck was running, I could look under the truck and see coolant REALLY dripping off. It was coming from the front of the motor and dripping under the water pump area. A buddy comes over and looks at it and determines from what he can tell that the water pump appears to be bad. This is now in addition to the other leak that I know I have somewhere that I think is at the back of the motor, but more on that later. So I trot down to the parts house and get a water pump and tear into the truck and replace it.

    I get it all put back together and fire up the truck and...................................... it still leaks just as bad as before. Trouble is, I now have no clue where to look. My friend who originally diagnosed it is now on vacation for two weeks and since funds are short I also can't take it to a shop to have them look at it. He also has a cooling system pressurizer that will pressurize the system with the vehicle off to help in spotting leaks. This is something we should have done in the first place, but at first blush, it really did look like the water pump was bad. On later inspection of the old pump, it does indeed look like it was either getting ready to go bad, or was at least contributing to my loss of coolant so changing it out was not necesarally a bad thing to do. It has now eliminated once possible source. While funds were short, the pump itself was only $60 so it's not a total misstep.

    So not knowing where to go since I can't tell with out tearing down the whole thing again where the leak is coming from and with the truck running, I can't see it with everything in the way, I park it till my friend comes home and can help me tear it down and check it out. While talking to him and letting him know what happened, he then says it is probably the intake and confirms what seems to be common even on this thread. He says it is probably the intake. So today, we are able to finally work on it.

    I take it over to his house and we start tearing into it. We first put his pressurizer on it and we can see it bubbling and pushing a little bit of coolant out from the under the intake on the front passenger side of the motor. So we have confirmed what looks like a "minor" leak and could be my leak that I saw with coolant dripping from the back of the motor, in that the coolant would run down the valley between the valve cover and intake and off the back of the motor (in theory).

    So we start to tear everything off that is in the way so we can see the entire cooling system. Alternator, alternator brackets, power steering, A/C, clutch fan, idler pully, tensioner pulley, air box and mass air flow sensor and air tube. Anything that was in the way of looking at the cooling system that we could take off with out breaking into the cooling system we removed. Now we can see. We hook up our pressure tester and pressurize the system. Immediately we can see at the front of the motor where I had initially been looking water just pouring out. You couldn't see it before because the alternator was in the way. But there was a definite intake leak right there. It just poured out and ran down the front of the motor. Another concern I had was maybe I didn't get the new water pump sealed and mated properly to the block, but that checked out fine.

    On to part II
  • the_big_althe_big_al Member Posts: 1,079
    So that sealed it. Off to the parts store I went while my buddy started to tear down the rest of the motor. While we were in there we decided to go ahead and do valve cover gaskets as well since they were also leaking and they were covered dirty grime from the bolt gaskets seeping a bit and also they were leaking a little where they mated to the head. I got back and we finished pulling everything apart. Upon removal of the intake manifold, we could definitely see where it had been leaking. It was actually leaking in a couple of spots. The front of the motor was the worst. It had almost completely disintegrated (luckily it decided to leak externally only). We cleaned it all up, pulled the valve covers, cleaned them all up and put them back into place and then proceeded to get the new gaskets in place and the front and back of the motor siliconed. Back on with the intake and then back together everything we had torn apart.

    Before starting the truck though, we decided to pressure test it again to make sure there were no leaks. We hooked the pressure tester up and immediately we could hear it losing pressure somewhere. So we start poking around for the source and find it at the upper radiator hose where it mates with the T-stat housing tube. After hunting for a new hose clamp and finding one an hour later after going back to the parts house, we get that taken care. Pressure again and now we can see it dripping still. Another bad hose clamp (we should have just replaced ALL the spring loaded, but we didn't. We replaced that one and now all the clamps that we have removed are no longer the spring loaded ones, but the screw down type. We pressure again and FINALLY seem to be holding pressure and have no leaks, drips or hissing.

    We start the truck and AMAZINGLY it fires right up. I say amazingly because we had this thing ALL the way apart practically. Electrical connections were all unplugged, vacuum lines disconnected, distributor taken out and so to have it turn over on the first try as if it had never been apart was really quite amazing. We let it run and inspected for leaks all over. Let it get to operating temperature making sure we added coolant as it needed it. It pushed a lot of air out and finally after running several minutes the T-stat opened and began to draw coolant in and the heater got warm.

    We let it run several more minutes, making sure the coolant level stayed full and also checking for drips and leaks. After seeing none, we closed her down, and I came home! It appears that we have fixed it. (Hopefully)... I'll keep my eye on it for a few days and won't venture to far from home, but I think all will be well. Hopefully we took care of that minor oil leak I had too in the process. That would be nice.
  • gonogogonogo Member Posts: 879
    I think you got it too, great job.
  • themikeyjthemikeyj Member Posts: 1
    Did you ever figure out what the name of this pipe is? I am having what sounds like the exact same problem and I can't seem to find any information about this. I know this post is like 2 years old but I really help. Thank you!
  • gonogogonogo Member Posts: 879
    I would ask for the thermostat housing assy, might be a dealer only part. If it was mine, which is not leaking yet, I would try to pull the tube out of the housing and reseal it.
  • kushinloud10kushinloud10 Member Posts: 1
    I just recently replaced a water pump on my 1992 s-10 Chevy pickup. Before this coolant leaked everywhere. So I tore everything apart, put the new part on, new gaskets and put rubber gasket sealer on the gaskets. I got everything all put back together. I believed it to be fixed because it quit leaking. The next day I drove the truck to school and noticed it to be leaking again. I found it to be a pinhole in one of the lines and fixed that as well. So all said and done I finally believed I got it, but the next day I was driving down the road and my temp. gauge went wayyy up. I stopped on the side of the road and checked the coolant it was all up to specs. So I continued to drive home. The truck drove fine and acted fine, and while i was driving, the temp. went back to normal and the check gauges light went off. The temperature gauge now goes up for a few miles and then goes back to normal while i drive it. I'm really stumped on this one hopefully someone can help me out.

    Thanks... :confuse:
  • the_big_althe_big_al Member Posts: 1,079
    Did you change the thermostat?? That will make the temp gauge fluctuate if it's not working properly. The T-stat should be changed (or at least I did and would) when you change the water pump.

    You might also have air trapped in the system, especially since you broke it wide open changing the water pump. That air will cause the truck not to vacuum properly and won't push or pull water from the recovery tank. Try bleeding the system. Or taking it to a shop and having it flushed. They can do a pressure flush that will force any air out of the system...
  • xjdmoorexxjdmoorex Member Posts: 1
    i have a 94 s10 4.3 5spd i recently replaced the water pump due to over heating and its still leaking somewhere i've bubbled the system a few times then come out the next day and the coolant had leaked there a soft plug around the waterpump area??
  • the_big_althe_big_al Member Posts: 1,079
    I've been there done that with cooling issues on my 4.3 I had a while back. Do you have a pressure tester that you can use to pressurize the system with the motor off? IF not, can you rent one or borrow one from a store or friend. I would do this, even buy one, if it's not too expensive.

    Then pressurize the system with the motor off. You do this by replacing the cap with the pressure tester. It pressurizes the system and will expose any coolant leaks. You can then trace them with out fear of moving parts and fans and belts and pulleys and with out the noise of the motor running.

    Here are typical problem areas I experienced and found are typical of the 4.3. I did this on a later generation 4.3 (2001) so I am not sure how much will have changed, but the basic block configuration didn't change much. Heads and intakes changed, but not much else. My 4.3 had a lower intake gasket leak. It was spewing coolant into the valley where the valve covers, intake and heads came together. 4.3's are prone to this leak.

    Since you also state you overheated, you might have cracked or warped a head. Especially if you have aluminum vortec heads. If that's the case, you'll have to tear down and replace the affected head. The pressure test though will tell you where it's leaking, unless it's leaking internally into the block. If that's the case, your oil will be full of water.
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