hey guys. I've got an 01 TJ1 auto with just over 110,000 on the clock. Whenever i run it for a while (anything over about 10 mins) the temp gauge sits 1-2 lines over halfway. The car pretty recently had its 100,000 service, its got new coolant, new oil about 1000 kms ago and as far as i'm aware (and the mechanic i asked about it when he did the timing belt) nothing obvious is wrong with the car that would make it run hot.

Its consistently 1-2ish lines above halfway, never goes higher and once it gets there, the temp stays consistent. I'm not losing any coolant, and air flow is fine to both the radiator and the air intake. Judging by the consistency i'm starting to think that it might just be the gauge showing a bit higher than it does on most, but its not something that's really normal...

any body else had anything like this?

maybe a small air pocket in the cooling system?
try running the car for a while with the heater on and without the radiator cap on (until warm) this should let any small pockets of air out (if any at all)

Forget the heater as the Third gen's do not turn the heaters off, they only divert the air

You either have a dodgy thermostat or perhaps the fans are not comming on

When it warms up, switch on the aircon to hit the fans, does the temp go down

Could also be an electrical issue in the dash so it is reading high when the engine temp is fine

i've done the air pocket fix already, didnt change anything, and air con didnt make any difference during summer. Having the heater on did make a difference, but only when the heater was on. I'm starting to think thermostat

Do a quick search - there have been at least 2 similar threads in last fortnight, with details of overheating checks and diagnosis; plus about 2 more threads focussed specifically on problems with fans (either not runnning, or not stopping).

Some good ideas were posted-up. Use the workshop manuals in links from Tech Torque forum, if yu are able to access the PDF's of genuine Mitsi Workshop Manuals. (links occasionally fail).

So before the service and timing belt change how was the temp gauge reading?

Have you removed the radiator to get rid of all the rubbish, grasshoppers, bugs etc that get between the two cores? If it hasn't been cleaned for a while there could be a 100-150mm of the core blocked at the bottom, and corroding of the fins.

Its a good idea to remove the radiator every 2 yrs and clean both the A/C and radiator cores, then replace the coolant. If the cores have a lot of hard, dry bugs blocking the fins then soak it in a tub(or kids pool) for a few hours, carefully reverse hose the bugs out. Don't hose from the front. If the fins are weak and corroded the pressure will destroy them. Then poke any remaining bugs out with fine wire. Again be careful not to puncture the core tubes. Then give the core a good coat of paint to protect it from further corrosion. The A/C core needs a hose out too.

If the engine was running hot before the service then the thermostat may be jamming and not opening fully.

If the hot running started after the service the possibility is that the mechanic mucked up the belt replacement. If he got one cam retarded by one tooth the engine would still run but will generally be a bit hotter, but except in very hot conditions a healthy thermostat should compensate and get the temp back to normal.

Cheers,
Alan

mine was doing this, i diluted my coolent with some water, that fixed it, i think it was running too much anti-freeze,
as this does not seam to conduct the heat very well, the water is important,
only reason anti-freeze is used, is for its rust protection and anti freeze/boil properties

took it for a highway run today. I'm 95% sure its thermostat related. Was right on half way when i was cruising, then raised 2 lines if i stopped at lights for anything more than about 30 seconds. might try cleaning the radiator first since its free, but think i'm up for a new thermostat. 60 bucks at supercheap too! lame. hopefully repco can do better

took it for a highway run today. I'm 95% sure its thermostat related. Was right on half way when i was cruising, then raised 2 lines if i stopped at lights for anything more than about 30 seconds. might try cleaning the radiator first since its free, but think i'm up for a new thermostat. 60 bucks at supercheap too! lame. hopefully repco can do better
3.5L Thermostats are expensive so don't expect the price to differ THAT much.

it was 80 all up, less staff discount =$60. so i know its not going down too much from there. If only i could mod a commodore thermostat...... $13 or something

well repco have them for $43. So even with 25% staff discount, thats still a fair bit cheaper than supercheap. For somebody without staff dicscount it would be half price...

and they wonder why supercheap doesnt do many special orders...

Forget the heater as the Third gen's do not turn the heaters off, they only divert the air

You either have a dodgy thermostat or perhaps the fans are not comming on

When it warms up, switch on the aircon to hit the fans, does the temp go down

Could also be an electrical issue in the dash so it is reading high when the engine temp is fine

Sorry to resurrect this old thread, but I am experiencing the same problems:
It overheats when in traffic for longer that 5 mins, the temp goes back down when I switch on A/C. What does that mean? I've changed the thermostat, flushed out the radiator, I haven't changed the cap yet, but I'll give it a go this arvo. Otherwise the temperature slowly goes down to normal after resuming driving but it takes time and kms.

any ideas?

Sounds like to cooling fan(s) are not switching on - the coolant temp sensor should turn them on when the temp goes above a certain temperature so I'd check the fan relay and also connections going to the fan. There is probably also a fuse somewhere in the circuit. At a guess I'd say it is not the sensor giving trouble as if this is the case you get either hard starting or excessive fuel consumption due to the ECU not knowing if the engine is hot or cold. Once you start driving, the flow of air thru the radiator is sufficient to cool the engine.

The fan switches on and is working, but it seems like it is not enough to cool the coolant. Interesting that you mentioned excessive fuel consumption, it's a lot higher than normal, sitting on 14.8 where as before it was 12.5 to 13.5. Maybe it is a thermo switch? Another thing I've noticed is that the temperature drops below middle when the AC is turned on. How much are the switches, does anyone know?

The fan switches on and is working, but it seems like it is not enough to cool the coolant. Interesting that you mentioned excessive fuel consumption, it's a lot higher than normal, sitting on 14.8 where as before it was 12.5 to 13.5. Maybe it is a thermo switch? Another thing I've noticed is that the temperature drops below middle when the AC is turned on. How much are the switches, does anyone know?

Are you sure the fan comes on when hot? - you say"It overheats when in traffic for longer that 5 mins, the temp goes back down when I switch on A/C. " ......have you noticed if both fans come on or only the A/C fan. Once my engine reaches operating temperature (half dial), as soon as the car stops at lights, you hear a click and the fan comes on...almost as though when the car ceases forward motion it knows the engine will heat up so it turns the fan on.
There will be a test procedure got the coolant temp sensor.....on GM cars you remove the connection and run the engine, fan should come on after a few seconds - but I'm not sure if that would work on Mitsu.

I've tested the fans and they turn on when the temperature is half way, then I drove the car for 5 mins and left it running in the driveway to see if it will overheat and nothing, the temperature was stable, then the following day after driving for 5 mins then got stuck in traffic and the temperature went up eventhough the fan was working???? I guess I'll switch oin the air con to cool the car unitl I figure out what's causing the issue. Thanks for you help hako!!

I've tested the fans and they turn on when the temperature is half way, then I drove the car for 5 mins and left it running in the driveway to see if it will overheat and nothing, the temperature was stable, then the following day after driving for 5 mins then got stuck in traffic and the temperature went up eventhough the fan was working???? I guess I'll switch oin the air con to cool the car unitl I figure out what's causing the issue. Thanks for you help hako!!

When you say "then the following day after driving for 5 mins then got stuck in traffic and the temperature went up eventhough the fan was working????", are sure the fan was working....or are you assuming the fan was working. Reason I ask is that if the fan relay is dodgy, it may not always work, and then work other times.....or if you have a loose wire somewhere in the circuit, the same thing may happen. Another question: when you say the car overheats, exactly what makes you think it is overheating - gauge indication, boiling or what?
I'll have to look at mine to see where the relay is....on Commodores you can swap the relays around if you suspect the relay but the Magna may be different..

Hey guys, I have the exact same issue with my KJ Verada. I replaced the thermostat with an OEM unit and the only difference that has made is that the temp on the gauge now sits just below half way when cruising on the freeway. Once off the freeway, the temp will rise about 2 bars. That's when the fans kick in and it gets back to normal.

Any other ideas?

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Somehow I figured out what happened to my magna. The temperature used to go up 2 bars when stopping at the lights even after the fan kicked in, but it would only go down to normal after I turn the A/C on, which would trigger the other fan to turn on. So I thought the cooling fan was not spinning fast enough to cool the radiator, then I tested the fan for Low, Mid and High and it worked it all 3 modes. Then I replaced all three fans relays (low,mid,hi) and next time the fan kicked in the you could feel the difference with the noise it was making, it sounded a lot more powerful. Now the temperature sits bang smack in the middle, so I came to the conclusion that it was the fans relays that were faulty, after a lot of ##$%ing around/.