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Overheating(what's the problem?)



  • app1nagapp1nag Posts: 15
    Wow...that was a fast reply...thanks for the info on the hot you know if replacing the thermo switch and relay is a difficult procedure? It appears you feel that these are two distinct problems: one being the overheating and the other being the coolant loss.
  • gchernya1gchernya1 Posts: 43
    I've met situation when overheating was caused by sleeping belt, that in it's turn did it because a high rolling resistance of one of the components engaged through this belt. As a preventive measure I shortened fan relay to make it start a fan together with ignition on. It helped somewhat, until real problem - faulty tensioner, pronounce itself clear enough. You can try this approach as cheep alternative to above mentioned replacements. Sure, warm up will take little longer with fan on, but this is not a problem at this point.
  • ratchratch Posts: 21
    Some bits of wit when overheating happens:

    Low/no coolant. No or intermittent heat from heater.

    Coolant, but...
    temperature climbs going down the road -- poor circulation through radiator -- (1) clogged radiator (2) water pump/belt problem (3) collapsing suction side radiator hose -- very rare.

    temperature climbs while stopped on idle -- normal until fans kick in. If it still climbs -- (1) bad thermostat (2) clogged radiator -- inside or out (3) water pump/belt problem.

    Hot engine, coolant overflowing and blowing -- (1) bad thermostat (2) slipping water pump belt (3) slipping water pump impeller.

    Hot engine, no overflow or only steam -- low/no coolant.

    Thermostats can be checked. Put a candy thermometer in radiator with cap off (on cars which can be run with an open system). Observe coolant temp when circulation starts.

    If engine won't normalize (modern high efficiency), remove thermostat from cold engine, test in a pan of water with a candy thermometer. Look on thermostat for temp range. Most start opening just before water boils, some just after if at high altitude. Bad ones either don't open or open very little in boiling water.

    Bad thermostats can be intermittent.

    Test new thermostats before installing -- I have had three bad thermostats right out of the package.
  • Mr_ShiftrightMr_Shiftright Sonoma, CaliforniaPosts: 58,504
    ah, the golden rule of good diagnostics...never assume a new part is a good part.

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  • ChingCChingC Posts: 11
    If coolant disappear in a small amount randomly, not regularly, and there is no leaking in the system, what could be the problems; head gasket leaking, cracking, belt slipping, ???, and what will be the suggested remedies?
    Thanks for the advise.
  • spokanespokane Posts: 514
    Random loss of coolant, with no apparent external leakage, is not likely to be associated with a slipping drive belt. It could be a head gasket or cracked head, but if the car otherwise runs OK and you have no odor of burned ethylene glycol, it's suggested you look further for leakage.

    The coolant pump will sometimes leak during running but not leak when stopped you don't see any coolant on your garage floor. Look carefully at the weep hole on the bottom of the pump housing; you may need a flashlight and small mirror to be able to see it. A small amount of residue at the weep hole is normal but if you see coolant drooling out, replace the pump. Careful checks of the radiator and all hose connections may also reveal residue that indicates a leak which evaporates rapidly such you you don't find drippage on the garage floor. Also check the heater housing and carpeting beneath the heater to see if the heater is leaking.

    Hopefully, your problem is some type of external leak rather than an internal engine problem.
  • ChingCChingC Posts: 11
    to spokane

    Thanks for your quick response and suggestion. It makes sense. However, I still can not locate any obvious leak. If it is the head gasket, can the head be re-torqued, so that the gasket is sealed to stop the possible leak? Of course, it is not going to work if the head is cracked. But, what is the risk to re-torque the head if the manufacturer's procedures is followed? Is there any test that can be done to pin point the problems associated with head, such as gasket or cracked head?
  • spokanespokane Posts: 514
    Good question, ChingC, on re-torqueing the head. My experience is that once a head gasket has begun to leak, it is very unlikely that re-torqueing will enable it to re-seal. However, it can't hurt to retorque if you follow manufacturer's spec as to bolt sequence and torque level.

    Pleas note the above posts 21-26 regarding the odor that usually accompanies a coolant leak into a combustion chamber.

    Another check: If coolant is getting into a combustion chamber, sometimes the coolant's green-yellow color can be seen baked into the residue on the spark plug. Remove the plugs and inspect them carefully. This is not a certain test; it's possible to have such a leak and not find the green-yellow residue.

    If the engine is performing OK and you don't have the above symptoms of an internal leak, I would not remove the cylinder head until I had a careful inspection done by someone well qualified in solving cooling system problems.

    What kind of engine do you have? Please let us know what you find.
  • ChingCChingC Posts: 11
    Thanks again. I will check the spark plugs carefully. Mine is 87 Mbz 300E about 100K mile.(bought used at 75K miles) It is a great car, however, there are lots of minor nuisances and repairs, etc.

    I have been talking to several mechanics, about the possible causes of the coolant loss. And, so far, I haven't find someone that I feel comfortable to turn the car in yet. Beside, it is a minor leak/loss at this point. Mbz uses a colorless ethylene glycol solution, therefore, the baked color may not be there. But, I will try to find out myself when I got a chance. One auto part store suggests a kind fluid to be added to the coolant. Under the timing gun light, you will see a different "light/color" at where the coolant leaks. It sounds pretty good, however, I havn't have guz to try it yet.

    So far, I did not smell the odor of the burned ethylene glycol as discussed.
  • Mr_ShiftrightMr_Shiftright Sonoma, CaliforniaPosts: 58,504
    Has the cooling system been pressure tested yet?

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  • ChingCChingC Posts: 11
    Two pressure tests done by two mechanics can not locate any leak.

    When the car is idling at intersection in hot days (outside air at 85 deg C), I can see the water temperature goes up from approximately 70 to 85 deg C. Coincidentally, more water is consumed at 85 deg C. I guess that at a higher water temperature/pressure, it leaks more. I need to add 10 oz water or so in a hot week. I did not have chance yet to hear a third opinion, but plan to do so in about 3-4 weeks.
  • spokanespokane Posts: 514
    You are surely correct in your observation that most causes of coolant loss would associate a higher loss rate with higher pressure/temperature. However, your temperature information is curious. I don't know the exact Mercedes specification, but a temperature of 70C is rather low. I would expect the temp to range between about 92C and 106C, depending on load, speed, and electric fan cycling. It seems that your temperature readings are incorrect or you thermostat is defective. A too-low operating temperature contributes to excessive engine wear.

    However, ChingC, a low-temperature coolant problem does not explain the coolant loss which is the basis of your concern.
  • ChingCChingC Posts: 11
    The temperature readings are from the gage in the panel. It is not calibrated and may not be correct. However, the Mbz is equipped with an inductive type engine driven mechanical fan at a low rpm. This may explain why the normal coolant temperature is low, around 75C. I could not find any normal temperature spec from the Service Manual. I tried to idle the engine to allow kicking in the electrical driven auxillary fan. The auxillary fan shall be kicked in at coolant temperature of 110C, however, I can not get the coolant temperature up to there.

    Anyhow, I am talking to another Mbz mechanic. He mentions that the Mbz's engine freeze plugs are cheap gage metal made instead of brass type, and therefore, it may leak due to corrosion. There shall be white residue around the leaking places. He pretty much agrees with you on the other possible visible spots for the causes, such as circulating pump drain hole, radiator drains, etc.

    As for the coolant burning smell at the exhaust, he feels that one may not be able to smell anything for a small coolant consumption.

    What shall be done on the car? His suggestion is that all "external" related cooling loss causes, such as freeze plug, radiator, circulating pumps, etc. must be ruled out first, say, with 95% certainty, before considering the head job, which is an expansive "internal" problem, $1000-1300. The alternate option is to keep on driving until the problem gets worse. Then, you know for sure that it is a head problem, assuming there are no other visible "external" problems. Anyway, I am planning to have him check it up, and the tentative appointment is set approximately two weeks from now.
  • spokanespokane Posts: 514
    I agree with your mechanic's comments. Even though he has not yet clearly identified the coolant-loss problem, I believe he's on the right track. I am not familiar with the colorless anti-freeze solutions; you may want to ask him about the possible use of Prestone brand antifreeze or some tracer additive that M-B recommends. As he suggests, you certainly do want to investigate all possible external leak sources thoroughly before considering cylinder head removal.

    As to temperature, I expect you do not have a problem because the dashboard gauge is often just a rough indicator. You could attach a thermocouple to the hot water outlet, cover it with insulation, and compare the readings with the dashboard gauge. You could then place a piece of cardboard in front of the radiator; this would force the temperature to 110+C even with the inductive primary fan running and provide a check of the secondary fan operation. If you don't have an accurate independent temperature device such as the thermocouple, however, you risk overheating with the "cardboard" procedure. In that case, ask the shop to do a temperature and auxiliary fan check.
  • ChingCChingC Posts: 11
    Thanks for the suggestion. Mbz's cooling system is not "typical". In other words, there is no cap on the radiator. The overflow tank appears to be part of the system. I suspect that it is a "semi-closed" system, i.e. the operating pressure is somewhat higher than usual. I have no clue though. As for the thermocouple option, it may not work, because the cooling water pressure will exceed one atmospheric at a temperatue exceeding 100 C. In other words, water will splash out of the tank if it is not capped, and I am quite sure to make it safe with a thermocouple.
  • the cars' temp. guage has been going up and down on the highway. Now it goes up and overheats. The thermostat has been replaced several times and it has been to the Pontiac garage. They can not find the problem. Can anyone help?
  • I have a 1994 Toyota Corolla which has undergone regular maintenance checks and has had oil and fluids checked every 3,000 miles. Last Sunday after driving it for 15 minutes white smoke started spewing out of the engine and the engine light went on. Now the car is in the shop to the tune of $4,000.00 for a new/re-built engine and a new radiator, etc. Has anyone ever had this happen to them? What could the cause have been? Thanks, enginewoes
  • bobs5bobs5 Posts: 557
    Sounds like a head gasket went bad and coolent is now getting into a cylinder of the engine.
    We had a 1979 Datsun 310 which the headgasket went bad on. Lots of white smoke!
  • About 1 year ago, the radiator on my 1991 Lexus ES250 was leaking and couldn't be fixed. I replaced the radiator with an after-market product. The radiator cap was different from the original and I didn't know it. I drove it until recently when the coolant started spilling out through the overflow tank on a regular basis. The dealer replaced one hose and identified the problem with the radiator cap. I replaced the cap with one that seems to fit right and coolant stopped being lost through the overflow. The problem now is that I have to top off the coolant in the radiator each morning.
    There is a slight smell of coolant in the car when the windows are closed but I don't see any leaks. Any ideas?
    By the way, the overheating problem only started happening when I brought my car to the dealer about a month ago. The engine was idling rough and I was told that my spark plug wires, distributor cap and rotor needed changing. I had them do this work along with replacing the spark plugs. Is it possible that the mechanic forgot to attach a hose or something that would cause me these problems?
    Please let me know. Thank you.
  • spokanespokane Posts: 514
    Boeing, I believe you are on the right track. Since you don't see any leaks but must add coolant regularly, it's likely that a heater hose was loosened and the leakage is on the inside of the firewall ...thus the coolant odor inside the car. A failed heater core is possible but is less likely than a leaking connection under the circumstances you describe. Pull the carpet away from the floorboard to check for dampness. I expect you have a drying out job to do as well as replacement/reconnection of the heater hose. Good luck; let us know what you find.
  • a few months ago I noticed the temperature gauge on my '94 escort always seemed to stay on "cold".. didn't think anything of it at the time, but now I've noticed if I drive the car fairly aggressively for more than half-hour or so- the gauge will go to "hot" completely bypassing the "normal" range; and the overflow tank overfills sending steam and that oh so lovely smell of coolant into the air. I had a mechanic check the thermostat, but he found nothing wrong ?? Now I'm trying to figure out exactly what the problem is
    any of you had similar problems or know a likely cause of my dilemma?
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