NHTSA — Engine And Engine Cooling: Cooling System Problems


hardly worth mentioning
Crashes / Fires:
0 / 0
Injuries / Deaths:
0 / 0
Average Mileage:
62,521 miles

About These NHTSA Complaints:

This data is from the NHTSA — the US gov't agency tasked with vehicle safety. Complaints are spread across multiple & redundant categories, & are not organized by problem.

So how do you find out what problems are occurring? For this NHTSA complaint data, the only way is to read through the comments below. Any duplicates or errors? It's not us.

2003 Mitsubishi Diamante cooling system problems

cooling system problem

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2003 Mitsubishi Diamante Owner Comments

problem #11

May 252011

Diamante 6-cyl

  • 71,677 miles


I have a 2003 Mitsubishi Diamante ls with 71677 miles on it all of the sudden my husband (the primary driver) tells me that every time he gets out of the car he feels light headed and nauseous. Days later the front windshield started fogging up while driving and after turning the car off (whether it is warm or cold outside) I googled why would this happen and have spoken with a few mechanics and they are telling me that it is the heater core going out, and that the reason why my husband is getting light headed and nauseous is because there is anti-freeze coming into the interior of the car which is very detrimental to your health. I have read a ton of complaints on different websites and they all say the same thing. I contacted Mitsubishi corporate today and spoke with a [xxx] in customer service and explained to her what was going on and asked why Mitsubishi has not done anything about this. First because of the health implications, secondly because of the safety issue of the windshield fogging up while you're driving to where you can't see and thirdly that from reading the complaints, the heater core is right above the computer in the car so if the heater core is leaking antifreeze, it could fry the computer and cause a possible crash if the car were to stop suddenly. She said that "seeing that I hadn't had the car into a dealership in the last year that there is nothing they can do about it". I told her that it just started and what was I suppose to do, look into my crystal ball and know a year ahead of time that the heater core was going to go out. This is ludicrous! ! ! Mitsubishi knows that this is a serious issue and are not doing one thing to fix it (by issuing a recall) where do we Diamante owners go to get some help? do we need to file a class action lawsuit as that seems like the only way a fire is going to get lit under them (corporations tend to act if it means losing tons of money) the car can't be driven and I'm still paying on it. Help! information redacted pursuant to the Freedom Of Information Act (FOIA), 5 U.S.C. 552(B)(6).

- Hayward, CA, USA

problem #10

Nov 042009


  • 60,000 miles
Anti-freeze leak on carpet passenger side near firewall fogged up windows check engine light comes on and off due to the leak the ECU started working awful.

- Chelsea, MA, USA

problem #9

Jan 212006


  • 50,000 miles
I purchased a used 2003 Mitsubishi Diamante from bankston Dodge in 2007. It was clean and ran well. There was an unusual odor inside, but smelled as if it could have been what the dealership used to clean the inside. It turned out to be anti-freeze. The vehicle had a heater core leak prior to our purchase. Recently the gas gauge has stopped working.

- Grand Prairie, TX, USA

problem #8

Aug 092008


  • 60,000 miles


I own a 2003 Mitsubishi Diamante, around 60K miles I started noticing a sweet smell from the vents and a constant fog when the heat or air was turned on in the car. After taking my car to the mechanic I was told that my heater core was busted. My car also sdriving in "safe mode" meaning I can only run in second gear which is burning a tank of gas every three day, I love 10 miles from work. My car flashed in neutral will in drive. After researching my problems I've notice well over 1000 posted via internet from other Mitsubishi Diamante owners having the same issue. Its hard to believe this vehicle has not be recalled. There are great risks of inhaling anti freeze which is seeping into the car through the floor boards and vents. I have an asthmatic child who has been driving in the car until the problem was brought to my attention. This leak may also make the computer system in the vehicle go out. Something needs to be done before an accident is caused or a life is taken.

- Worthington, OH, USA

problem #7

Apr 282008

Diamante 6-cyl

  • 114,132 miles
My transmission relay went out due to a leak heater core. The core has been leaking for some time and has fogged my windows so bad I could not see at times, having to pull over and wipe off the film. This is a serious problem with these cars.

- Fallbrook, CA, USA

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problem #6

Nov 282007

Diamante 6-cyl

  • Automatic transmission
  • 78,000 miles
I own a 2003 Diamante Mitsubishi. The problem started with a check engine light coming on, fogging the window with a fowl toxic smell then the car would not hardly move out gear. I was told that the car's heater core leaked onto the computer which caused the transmission relay to short out do to the computer failing. The computer was still under warranty at 78,000 miles but I still had to pay for the new computer system because I was told that it was the heater core that caused the computer to fail. This is such a poor design! the computer should have been protected in such a case...funny thing it is now that I have had to replace a heater core, a computer and a transmission relay at a cut wrenching cost of $3,675.58. I wrote a letter to the president of North America Mitsubishi that the heater core should be a recall but to no avail. I have all maintenance records on the Diamante so that was not what caused this heater failure. I do have the computer that was replaced. It is now April and the check engine light has come back on...now what?

- Nashville, TN, USA

problem #5

Mar 202008

Diamante 6-cyl

  • Automatic transmission
  • 20 miles


I have 2003 Mitsubishi Diamante. My "check engine" light came on, so I took it in for service, and my heater core was leaking on my computer...now it's going to cost me around 3,500 dollars....this is a very flawed design. There should be a recall on this item.

- Alta Loma, CA, USA

problem #4

Nov 132007

Diamante 6-cyl

  • Automatic transmission
  • 86,000 miles
This is a Mitsubishi Diamante 2003 ES. I'm experiencing a sweet smell of anti-freeze inside the car as soon as I turn on heating. Anti-freeze contains ethylene glycon and the fumes are highly toxic. Fixing the heater core will cost $1300. I am filing this complaint to ascertain that this is a very very common problem in Mitsubishi Diamante and Mitsubishi motors should be aware of three main risk associated with this: (1) the defect exposes customers to unusual level of toxic ethylene glycol which should not exceed 10-25 ppm levels (consult msds for ethylene glycol) (2) the leak can affect the car's microprocessor and poses a severe hazard for drivers. (3) faulty heater core makes the visibility difficult due to fogging of windshield thus putting the driver at greater risk. I will eventually fix the problem by spending $1300 if Mitsubishi refuses to issue a recall. Right now I am trying some radiator anti-leak to delay the costly repair. But I want NHTSA to be aware of the hazards that has been ignored by the manufacturer.

- Orlando, FL, USA

problem #3

Jun 192007

Diamante 6-cyl

  • Automatic transmission
  • 42,900 miles
Maple syrup smell from air vents then car started to overheat heatercore failure, antifreeze in floorboards on windshield and coming through air vents. A new heatercore installed very costly had to do work myself because warranty expired. Had to shampoo carpets and buy new floormats because the anitfreeze ruined them. After reading many complaints you would think that a recall would be made. Just because no deaths the consumer should suffer. What about the money that it took to make the repair. That was money taken from my family that we use to feed us and have shelter. Come on you have to authority to do something so why don't you.

- Kingston, OK, USA

problem #2

Nov 232005

Diamante 6-cyl

  • Automatic transmission
  • 60,000 miles
2003 Mitsubishi Diamante coolant leak inside the car. Steam fogging the windows and strong chemical odor leaving residue on windows. Quoted $1000 to repair, they say it needs a new heater core. It may not be the heater core, but just seals. I have bypassed the heater hoses and fortunately live in a warm area.

- Saratoga, CA, USA

problem #1

Nov 012006

Diamante 6-cyl

  • Automatic transmission
  • 65,000 miles
2003 Mitsubishi Diamante with 65000 miles. Noticed fog coming out of vents around the radio. It smelled like anti-freeze and created a fog on my windows that was bad enough to render the car undriveable. I was also getting an error message of P-1751. This refers to a problem with the transmission relay control. I took the car to a transmission shop and after diagnosing for two days, the mechanic told me that he had discovered a leaking heater coil that may or may not have damaged the PCM. Worst case scenario, $1600. It will at least cost $500, best case scenario. I uncovered numerous complaints from Diamante owners with models from a wide range of years who were experiencing the same problems. This is criminal negligence and I personally request an investigation to research how mistubishi has been getting away with this, for so long. The same exact problems are occurring on a frequent basis.

- Raleigh, NC, USA

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