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Pete, Technician
Category: Car
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Experience:  17 years automotive training and experience.
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Mitsubishi GTO (3000GT): Hi, I have a N/A 1994 (face-lift

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Hi, I have a N/A 1994 (face-lift model) Mitsubishi GTO (3000GT in the USA). It has an on-going overheating issue after it is driven at freeway speeds for half an hour. Shorter trips and even using full power repeatedly for less than this time and it won't overheat. Also around town I can drive all day and no problems. When it starts to overheat I can reduce the temperature by turning on the heater and also by switching overdrive off. As it revs higher or goes faster it cools down but this is a temporary fix. Once it starts to overheat it will continue to do so. The radiator has been dismantled and cleaned and new top tank fitted. New water pump fitted, new thermostat, new pressure cap and filler assembly and new hoses have all been fitted. There is no oil in the water or vice versa. No coolant loss (I have a white drop cloth under the car in the garage and it is unmarked) except when it overheats, no sign of any coolant in the exhaust. No head gasket symptoms at all. In fact it runs really well. I asked a transmission expert if the oil cooler could be causing the overheat and he says no. It's not A/C because it overheats with or without A/C turned on. Any ideas?
My name is XXXXX XXXXX I am a professional here at Just Answer/Pearl. I noticed that your question was not getting a response and thought I would see if you still need help with this.I apologize for the delay and I hope I can still assist you with this here.

Check and make sure the fins of the ac condenser are not bent or damaged as this will cause a lack of air flow through the radiator to cool the coolant properly.I have seen this occur before and usually ended up being a restriction in air flow through the condenser to the radiator or restriction in air flow through the fins at the radiator (most likely the radiator is o.k. if it has been cleaned and the fins checked.

If you have not had a block test done to verify this isn't exhaust heat and gases passing into the coolant at higher speeds this should be done.This wont show up as coolant in the oil or oil in the coolant or an external head gasket leak as the leak is internal and may only be occurring at higher speeds.

I would start with having these checked to see if a fault is found with one of these.If these checks/tests have been done already let me know and we can continue.

Thanks Pete
Customer: replied 3 years ago.

Hi Pete. Thanks for the reply. I'll check the condenser tomorrow and schedule a block test and see what it turns up. One other thought I had was could air pockets in the cooling system cause this? Thanks, David

Hi David.

Air packets can cause this here,if there is still air trapped in the cooling system this can cause this fault but if you have driven the vehicle or ran the engine and shut it down several times with this issue the air should have worked its way free.One way to make sure is there is a vacuum kit that can be used when putting in the coolant.The vacuum sucker pulls a vacuum on the coolant system removing all air and then the coolant is sucked into replace the vacuum pulled from it.Most shops and dealers use this type of kit to prevent trapped air.

Let me know what you come up with and if you need anything else.

Thanks Pete
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I am following up with you to see if you still needed help with your question you had asked.If my help didn't satisfy your question please let me know so we can continue.

Thanks Pete
Customer: replied 3 years ago.

Hi, I have checked out the condenser and cleaned out a few bugs but the fins seem undamaged and shouldn't be stopping air flow. Will get the block test done once I can make an appointment with the dealer. Thanks for your suggestions they're most helpful. Cheers, David


I am following up with you to see if you still needed help with your question you had asked.If my help didn't satisfy your question please let me know so we can continue.

Thanks Pete

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