Howdy, Stranger!

It looks like you're new here. If you want to get involved, click one of these buttons!

Have you purchased a new car in the last year and had it delivered to your home/office from a dealership? If so, a reporter would like to talk to you about it. Please reach out to [email protected] by end of day Sunday, December 9, and the Edmunds PR team may connect you with the journalist.
If you experience loading issues with the login/register form, please completely disable ad blocker or use an incognito or in-private window to log in.

Mitsubishi Diamante



  • Recently, I have been having problems with my heater core. I am wondering if you know where on the Diamante Owners Group site the procedure is listed to remove the heater core without removing the dash. I have looked and looked and I cannnot find it!!! Any help would be greatly appreciated!

  • vivonavivona Posts: 410
    The Diamante Owners Site is currently down for upgrade, but I had some of the articles copied into a Word document, so here is what I have:

    CYPRESS, CALIFORNIA 90630-5208
    (714) 372-6000 (310) 493-1235
    TELEFAX (714) 373-1020
    TELEX 683453
    P.O. BOX 6400
    CYPRESS, CALIFORNIA 90630-0064
    The next release of Tech Talk will have the following information regarding a possible fix for heater core leakage. We wanted to get this information to you as soon as possible due to the increased demand we are seeing on the heater core.

    Group 55 Heater, A/C, Ventilation

    Heater Core Gasket Availability 1997-2002 Diamante.
    Heater core leakage may be caused by damaged gaskets between the heater core tank and the connecting pipes. Replacement gaskets are now available (p/n MR925655).
    One yellow gasket is included per package.

    This was posted by an owner on the Diamante Owners website:
    Hey guys, today I took on the task of fixing the heater core in my D of course you know it was just the o-ring but I figured why replace with a part that I know will screw up again, so I tried adding in a black o-ring along with several beads on red RTV high temp silicone. I ran out of daylight , so I didn’t get the chance to reassemble my dash, but Just wanted to let you guys know that no you don’t have to take your whole dash apart to get the heater core out and no you don’t have to disconnect any a/c hoses, let me explain and if you have done the heater core on your own then you’ll understand.

    Take entire under part of dash out, and the wood grain center, radio, clock ashtray etc, under the dash there is a box that the a/c line runs into this looks similar to the heater core same principle but makes cold air blow into car, anyway this is a two piece plastic box with about 8 metal clips around it, take out the clips and the box comes apart, this is of major importance. Disassemble metal dash unibody pieces under and behind radio, and take the nuts for the heater core box off of firewall, four nuts, with some tricky maneuvering you can turn this box then take out three screws holding heater core feed line in place, voila! heater core comes out. Anyway back to the experiment with the different o-rings and rtv must set up for 24 hours, and for added security I am fabricating a splash shield for my ECU, just in case she doesn’t hold, but if it works I will let you know, or doesn’t, by the way total cost so far is estimated at 2.50.

    Hey rather than 900 labor from those thieves at the dealership, of the 15.00 a piece for the replacement faulty o-rings (two needed) I think I came out pretty good, almost too good, that’s why I putting a cover on my ECU, hate to try to save a few bucks then fork over 1500 for a new brain, hell I’m surprised it still works it was covered in antifreeze.

    Another posting about replacing the gaskets:
    Well, I finally got around to changing the heater core O-rings on my 2001 Diamante. Thinking about doing it was worse than actually doing it, not being sure if I could really get at the o-ring though the glove box, but it works. Hopefully, the procedure will work for the other 2nd generation cars as well.

    The most surprising thing that I found was that I believe that the leak was caused simply by loose screws where the pipes attach to the heater core.

    None of the screws were very tight. At this point, I'm not totally sure. The car started leaking about a month ago (the "sweet" odor, the vapor on the windsheild, etc.). Within a day or so, I put in some "Barr's Leak", to seal it up. The leak was definitely improved, though I could still smell the odor. I think that's normal. However, there is still a possibility that the actual core was leaking. If that's the case, there is also a good chance that the Barr's Leak will seal that up, more or less permanently. I didn't change the heater core. It's just that if the leak is simply loose screws, the flexing of the hoses (from the engine movement) could eventually loosen the screws more so that it would leak with the sealant. I'm not certain that the root cause was the loose bolts.

    I had a 79 Mustang that had a leak on the heater core, and found that the whole dash had to come out, so I tried the coolant sealant and it worked for the next 3 years that I owned the car.

    So, anyway, taking a hint from someone that posted here on the forum, that you don't need to remove the whole dash (I'd give him credit but the posting is gone from the "Heater Core Problems" that was on the forum).

    NOTE: This procedure allows you to change the heater core o-rings. I don't believe that you can actually remove the heater core from this procedure. I believe that the Instrument panel (dash) needs to come out for that.

    So, anyway, here's a procedure that should help if you want to attempt it yourself.

    As usual, no guarantees, you attempt this at your own risk.

    1. Disconnect the negative side of the battery. You'll be working around the passenger side air bag and you don't want that to go off!!!

    2. Order 2 (TWO) O-Ring gaskets, Mitsubishi Part Number MR927776, they were $2.65 each on-line + $9 shipping. For what it's worth, it appears that the newer ones are a different design. The original (from my 2001 D) has a ridge around the outer perimeter on one side only (though it could have been flattenend out from being installed). The new ones have a ridge around both sides, so I assume they seal better. HOWEVER, I just noticed another post that indicated that the TSB listed the MR925655 part. (Hope I didn't put in the wrong gasket!!!)

    3. Get the freon removed from the car. (I have a friend that removed and will recharge the system for me).

    4. Make sure the engine is cool. Drain the anti-freeze. You don't need to jack up the car. Put a pan under the front right of the car and reach down between the engine and radiator and turn the white plastic valve a few turns, and let it drain straight down, be patient (Don't remove the valve). Once the fluid is drained, tighten the valve again. You'll get about 1 gallon of anti-freeze mix.

    5. Remove ONLY one of the two heater hoses, closest to the passenger side, on the firewall. The other heater hose doesn't have to come off. I used a pointed nose pliers to squeeze the clamp, and pulled it back over the hose. You may have to turn the clamp to get good access. Put a towel below the hose to catch the coolant that will leak out and twist and then pull the hose off.

    6. Remove the 10mm bolt from the smaller AC line at the firewall, behind the engine, as well as the bolt that helps to attach the same line to the firewall (for extra play when sealing the line).

    7. Remove the 12mm nut from the larger AC line at the firewall. I found that a long extension and a flex
  • vivonavivona Posts: 410
    All of my previous message did not post, so here is the balance of the information:

    8. Seal the ends of the AC lines (I used plastic bags and rubber bands) to keep any debre out.

    9. Remove the rubber hose with the 90 degree bend located slightly to the right of the AC lines. This is the AC condensation drain hose.

    NOTE: When working under the dash, it helps to have a knee pad or something to kneel on.

    10. Moving inside the car, Remove the Under Cover assembly below the glove box. There are 3 plastic fasteners that pull straight out.

    11. Remove the Glove Box (2 Phillips screws) and then the glove box frame (4 Phillips screws). Use pointed nose pliers to remove the tabs that hold the wire to the top of the frame, and use a flat blade screwdriver to remove the connector on the top of the glove box frame. This connector goes to the passenger side air bag. Handle with care!

    12. Remove the metal frame bracket from under the glove box, being careful not to damage the wire to the light switch. Use a fine tipped screwdriver to pry the small connector catch (wrapped in foam to keep from rattling) so that connector pulls apart easily.

    13. Remove the left side heavy "Z" brackets from the round tubular frame from above the evaporator unit. The one on the right side doesn't have to come off, it won't be in the way.

    14. Remove the 2 12mm bolts at the top of the AC Evaporator and the 12mm nut at the bottom. Also disconnect the two connectors that are on the side of the evaporator.

    NOTE: You do not need to remove clips that hold the two halves of the evaporator housing, nor the black connector block on the right side, nor the black plastic piece on the left side of the box. NOTE: The fan assembly on the right side does NOT need to be removed.

    15. Pull the carpet back to make some extra room and so that when some of the AC oil leaks out, it won't get on the carpet.

    16. Now comes the tough part, getting the evaporator housing out. (i.e.: 10 lb evaporator, 5 lb opening!!). Pull it forward some, then bend the front down (toward the floor) and pull it around. Takes a bit of playing, but it will come out. There will be a bit of AC oil that drains out on the floor, but with the carpet pulled back, just wipe it off the underlayment floor surface. Shouldn’t be more than about 1/4 oz.

    NOTE: After re-installing the evaporator, I think that it might be wise to bend the metal bracket that holds the left side of the glove box (attached to the center console inside supports) back and out of the way. This should not only help in getting the box out, but also back in (which is WORSE than trying to get it out!)

    17. Looking up to the left, you'll see the hoses that are connected to the heater core. You won't be able to remove the heater core, but you will be able to remove the 4 screws (#20 torx head) from each of the two hose blocks. BUT FIRST put 2 or 3 towels on the floor (stuff them around the metal brackets) to keep the coolant from draining into the floor mats.

    18. You will be able to remove the upper black plastic hose end (twist it upward), but the other metal pipe is fairly firmlly entrenched. There is enough room to remove the plastic bracket between the hose and the heater core though, along with the o-ring.

    19. Spend some time cleaning up the anti-freeze from the area to help get rid of the smell, or it may be around for a long time. I did note that they put a piece of plastic on the top of the ECU (under the foot distributor duct) so reach in with a paper towel and wipe it off. There was some discussion on the board about covering it completely, but my concern (being an electronics engineer) that if you seal it too tight, it won't be able to cool as well as it needs to. Anyway, I used a squirt bottle to put some water around the heater core, but it doesn't drain out. Soak up the water with paper towels. (Anyone have a better idea on how to clean up?)

    NOTE: There is a plastic bezel that goes between the lower hose connection on the heater core, which surrounds the lower o-ring. There are some square prongs that stick out. These prongs go toward the heater core. Look at the upper plastic hose connection, it's essentially the same, but the piece with the prongs is not removable.

    20. I would suggest that when you are putting the heater core screws back in, with the new gaskets, that you add a touch of a medium strength lock-tite to the screws so there's less chance that they will work their way out again. Remember that the screws go into a plate of aluminum, about 1/8 inch thick.


    21. Be careful when putting the evaporator back in, not to damage the fitting surface. When re-installing the AC lines, don't over tighten. They are aluminum fittings. Handle with care.

    22. Getting the evaporator box back in is worse than trying to get it out. You're on your own here. I ended up breaking the black plastic bracket behind the left glove box support (so I bent the metal bracket back, as mentioned above). I just glued it back into place with a good epoxy. No one will ever see it.

    Reassembly is the reverse. Use new Anti-Freeze to replace what you've drained.
  • kninknin Posts: 5
    Just purchase a 98 Diamante yesterday (8/9/05) but didn't come with owner's manual. I'm thinking of buying one on ebay, but in the meantime, I want to do some maintenance work on it (oil change, spark plugs, etc). Can someone tell me what the recommended oil grade is for this vehicle and what the mile interval should be between each oil change? Also, what's the recommended octane fuel grading? Finally, I'm also experiencing vibration when braking but as I was making turns on the highway at 60-65 mph, I felt a "swing" or looseness at the tail end of the car more than once that made me apprehensive. I read on that the Diamante "suffers marked body lean in tight turns", can this be related to what I'm experiencing? Thanks in advance for your input, I appreciate it.

  • Good car; mine has 156,000 now. I use 20-50W or whatever my mechanic puts in it. After all it is just a Japanese 6 cylinder like any other. Change time? after 5,000 miles or maybe less. It just depends on whether I have to bring it in for anything else. But now a days I am getting convinced you cant do that too often (as in 3,000miles). 87 Octane works fine. the deciding factor is if you get ping.
    I dont quite understand the cornering thing but this is a strong engine with front wheel drive which isnt a great match in my opinion. Thats why race cars are still rear wheel drive.
  • Good car; mine has 156,000 miles. Car is assembled in Australia. Relatives over there call it a cadillac.
  • monireemoniree Posts: 6
    I have a 1992 diamante that is smoking. I am trying to figure if it is white smoke or blue (like everyone says to look for,) it seems to look more white. Anyway, it smokes after I drive a few miles, and when idiling. (Not usually when it is first started.) Its obviously burning oil. I took it to a mechanic that only looked at the smoke and said valve seals- $400. So, a guy wanted to buy the car and he took it to his mechanic, that once again by only looking at the smoke said piston rings - and said it was cheaper to replace the engine then to change piston rings. Then I read some past forums on diamantes that says that the valve guide goes bad and can cause it to smoke.
    So, I am confused on what it really is, and @ how much to fix. Any ideas appreciated. (V6 engine.) Also, other than that, car runs great! (I think it may have a small power steering fluid leak, I have to add fluid sometimes.) But like I said runs great other thank smoking.
    Thanks in advance!
  • 1racefan1racefan Posts: 932
    My local Mitsu dealer has an '04 Diamante LS with 15K miles on it on his pre-owned lot. The car is gold, and has beige leather interior. It is a sharp looking car, and he is asking $15,900 for it. I am curious to hear from some of the owners of newer model Diamantes as to whether or not you would reccomend the car to others. Has anyone had any major problems with these cars, or have most experiences been good? I have an Outlander, and have had a really good experience with the dealership. I know the Diamante was discontinued, and I am not worried about resale - I would just like feedback from owners as to how your cars have held up since you have owned them.
  • The last two times it has rained I can not start my 2001 diamante until it dries out. Car has 95,000 miles and has been well maintained, new battery. Any help would be great.
    Thanks Jeff
  • stemogstemog Posts: 3
    I have a 2001 Diamante and have been having trouble with the traction control. I'll be driving down the highway and all of a sudden lose the throttle with the engine still running and the TCL light starts flashing. I can't turn the TCL switch on or off while the engine is still running, but if I turn off the engine and re-start it, then turn it off it reads TCL off. Anyone have any idea if this is a computer problem or some sort of sensor problem? Thank you in advance.
  • could you let me know as well? I have the same problem. The radio asks for a code i do not have the woners manual. do you have a master code?


  • lori7lori7 Posts: 1
    I have a 99 D, and recently my AC & heater seem to be blocked. When I have either on you can hear the air moving, and gets louder and softer depending on the temp. it has reached. I am getting some air flow on my feet, and some by the windshield, but very little from all four vents. Just a light breeze comes from the vents. It almost seems like something is blocking the air path to the vents. Any ideas on where to look and what to look for?
  • stemogstemog Posts: 3
    I'm experiencing the same problem, though mine isn't only at low speeds, which makes it kind of dangerous. Was wondering if you came up with an answer yet? My mechanic is baffled by it and doesn't want to go guessing and changing expensive parts if he doesn't have to. He put it on the computer and it didn't throw out any codes. Just wondering if you got a solution? Thanks in advance.
  • I just bought a diamante with 115000 miles on it, every day something goes wrong, yesterday my air conditioning stopped blowing out the dash($400) I had to replace a seal in the transmission($300), had to replace the front CV axle($175), had to buy new ceraming brakes b/c the new non-ceraming squealed as loud as a damn jet engine (not to say it still doesnt squeal, but its not as bad) god knows where the squeal is coming from now. It rattles when going at high speeds. Thats about it, but i've only had the car for less than a month. I drove a nissan maxima before and didnt have a single problem in two and a half years. DONT BUY ANY MITSUBISHI.
  • ezorezor Posts: 4
    Hi my name is Ekrem from Columbia,MO.
    I have problem with my Diamante 93 Sedan. My car security anti-theft system was on when my car battery died. I opened car with the key and change the battery. After that i could not arm my car security again and also my car door automatic locks behaves in a strange way. When I reach a certain speed, door is locked automatically. This is okey but when I stopped in the traffic lights or somewhere without opening the door and drive and reach the same certain speed again, it locks the doors again although it is locked in the begining.. So, Does anybody know how to solve these problem ?
  • 2 months ago I bought my daughter a 93 diamante for $3000 at a used lot against my better judgment, but she loved the car.... the day after we got it home it stared smoking..... but still drove ok. Yesterday she went on a 50 mile trip to a nearby town and broke down, we had it towed, and after paying the guy a couple hundred bucks to check it over , he said we should cut our losses and just get rid of it, or sell it to a wrecker. he never even gave us a the main reason the car wasn't running, and actually, it was running, you just had to keep the rpm's up and feet on both pedals or it will die....but we managed to get it home. he also said it might be something computer related?? anyone have any ideas??? or a similar problem??? this guy made it sound like we have to tow it tow it home too...and we didn't.....?????
  • vivonavivona Posts: 410
    I am more familiar with the second generation Diamante, so I can only guess at your solution. Many cars have a default mode of operation that they will return to when the battery if removed. After you put in a new battery, you have to set things back the way you want them. It is possible that the alarm system needs to be set back up. Check your owner's manual for instructions.

    Mr. Vivona
  • vivonavivona Posts: 410
    The first generation Diamante's are known for smoking due to valve guide seals leaking. That is an expensive repair, but many choose to continue driving and living with the smoking.

    The car not wanting to keep running at idle is most likely related to a the Throttle Position Sensor, the engine computer, or possibly a very dirty throttle body.

    The TPS can be bought at wholesale through

    If it is the computer, you can have it repaired at for far less than the cost of of a new one.

    If it is a dirty throttle body, follow these instructions:

    Mr. Vivona
  • So sorry for not seeing this post sooner. I just experienced this exact problem and ended up solving it at about 1/4 of the cost the dealer originally wanted. I don't have the part numbers with me, but I ended up replacing two sensors in the throttle body. It's been about three weeks since the repair and I have experienced no trouble at all. I bought the parts on the Mentor Mitsubishi website and had the dealer put them in. The total cost was $215 for the parts and $200 for labor. The dealer originally wanted to replace the entire throttle body for about $1,600. Let me know if you need the exact OEM part numbers and I'll look them up off line. Good luck.
  • stemogstemog Posts: 3
    Thanks, Hank. Actually, I had mine to our local Mitsubishi dealer and they said the throttle plate was sticking due to carbon buildup, so they suggested trying having it cleaned first before spending the $1,600 for a new throttle body. I spent $238 for the cleaning (which I still think is a lot of money) and that was two weeks ago. No problems since, but my problem didn't happen all the time anyway, so I'm still not sure the problem is solved. If it does re-occur, I may take you up on your offer, or if you have the OEM part numbers feel free to post them. Thanks again and good luck with your vehicle as well.
  • Hi,
    I have bought a 99 Diamante and the Radio doesnt work for that. It asks me for a security code. I called up the dealer and tried to find out if they will help me by providing the code. They all are charging around $50 - $75 for that. Is there any other way I can get the code. I dont know how to remove the Radio out to find the serial number etc. If there is some master code or some other way I would be really thankful. Any help is appreicated.

  • rayk3rayk3 Posts: 9
    I have faced a situation that might be interesting to many Diamante owners.
    The guy replaced the battery and the sound system continued to work. How about the code that one has to enter after the the battery is disconnected in order to make radio work? The guy did not know the code, he does not work for dealership, and the code numbers I keep separately from the car... Isn't it odd? . Maybe, it is normal occurence for the older cars( mine is 97)? I'd appreciate any input. The thing is that I cannot get in touch with the guy to ask him directly. The battery is obviously different from my old one, so I cannot doubt that the replacerment was done.
  • ezorezor Posts: 4
    For smoke, it is probably because of valve stem seals. It is a cronical problem for mitsubishi 90's. You can use Begdhal No Smoke in Walmart. You should add this in each oil change and use 20x50 oil.. No Smoke in my car after that..

    About rpm, you can increase its rpm.. Follow the Gas pedal wire, there are some bolts you can play.. Also, there is screw on trottle body, you can increase the oxygen level by playing with it..
    I hope they solve your problems..
  • ezorezor Posts: 4
    You should also make sure, you did not put water more than enough to the engine cooler external cup. Wait to check water level when the car is warm. Because it is increasing when it is warm..

    Also check radiator cap, it must have all rubbers for insulation on it and also have small moving stuff below. If is is not working properly, the pressure will be low in water circulation in engine. This causes overheat and smoke....
  • ezorezor Posts: 4
    Use Begdahl No Smoke with 20x50 oil. Check External Engine Cooler Cup, donot overfill. Wait to check its level when the car is warm.. Also check radiator cup if it is working properly...
  • If you dig a little deeper, you will find that you do have a good car, but may need some repairs to the not-so-obvious problem. I have purchased 2 Diamantes in the last year because they are great buy of Japanese engineering for the price. I paid about the same price as you did, but had to put some money in brakes and an ECM (engine control module), which is possibly what is causing your problem. After having a dealer tell me that it was bad and that it would cost around $1,400, I researched on my own and found that I could get it rebuilt in Florida for $195. It worked out great! Let me know if you would like more information. P.S. Your towing guy probably is not familiar with these cars.
  • i just removed the radio from my sons wasn't too bad
  • mwinnmwinn Posts: 2
    I am trying to remove the radio from my 1995 Diamante Wagon to replace it, and am having a devil of a time removing the fascia around it. What's the secret???

    By the way, to keep from having to reenter codes, try rigging up a temporary 12v bypass around the battery when you are ready to remove it. Keeps the trickle of power to the radio so it won't forget its code.
  • wow!! my car takes forever to increase speed when i am getting on the highway. I am always getting cursed out by people on the expressway, because I am going so slow.
  • massodmassod Posts: 10
    I own a D/99. it has 75k miles on it. the "service engine soon" light goes on and off. what might cause the light to come on? can I fix it myself? :mad:
Sign In or Register to comment.