rising temp

[Scanny]

just cruising on the motorway at 75 i noticed the temp was up to just under 2/3 so i backed off to 70 and it dropped a little. it remained there at that speed and dropped a little as i backed off a bit. i had the climate control turned off (switched off using the bottom left hand button, not just using the down arrow) so i opened the centre vents and blew some hot air in to see if it was hot and it was, not only that but the temp gauge immediately returned to normal temp. i am letting the car cool now before i check my levels but i cant see why allowing air to run into the cabin would regulate the engine temperature. even sat in traffic without the heater actually blowing but not turned off was fine and the gauge was normal. i reverse into my drive so i did check the road to see if i had a leak but not a drop.
any ideas?

[The Vee]

First thing air lock, check rad as well as header tank. Sticking thermostat not allowing proper circulation, putting on heater will certainly take heat out of primary circuit, blocked radiator, same issues, and possibly knackered water pump. Of course check for any leaks, but your rad will be low if there are

[Scanny]

just had a look. i didnt even get the rad cap off and a dribble of coolant made its way out. the overflow is up to the top line too. this has happened occasionally before but only at higher speeds and not very often. is it worth asking for a quick check while the car is in having the headlight replaced?

[The Vee]

Might as well. Take the fans are turning

[Scanny]

they must be. as i said, stuck in traffic it was fine. i was there for about 10 minutes in roadworks which werent there when i went to work last night and there was no problem at all. the critical factor does appear to be that off button on the climate control panel which i think is bizarre but i dont know anything about mechanics. when i was in the roadworks i didnt have the heaters blowing. the air was flowing from outside rather than recycled air but i was stationary. this problem only happens at motorway speeds which is normally when a car is more efficiently cooled isnt it? my supra had a serious problem which meant i had to avoid slow traffic at all costs or the temperature went right up. this problem is the opposite although it is thankfully intermittant

[bradc]

It sounds like the cooling system can't handle the increased load of driving at high speeds when the engine is making a bit of power. The fans won't be having any effect at all at those sort of speeds.

The heater works because of course it gets it's hot air from the engine. It could be an airlock perhaps if the temperature drops down really quick as you describe.

[crazyken76]

check you thermostat and engine oil for water mixed in it

[Davezj]

my bet would be sticky thermostat or air lock in the cooling system somewhere.

from cold with the engine running (you will have to be quick as the water in the cooling system heats up quite quickly), you could try opening the air bleed screw on the top thermstat housing, to see if air comes out of that. if it only bleeds water then then do the screw back up.
next keep an eye on the temp gauge, but check the Rad top hose to see if it getting hot or not if it does not get hot the the thermostat might not be working correctly. the top hose can take quite a while to get hot, as the thermostat has to open to allow the hot water to flow.
as long as the temp gauge doesn't go above half way ish then you can just wait for the thermostat to open. but it should have opened within about ten minutes of starting the engine though.

[Turbo_Steve]

First of all: airlock!
You will usually be able to hear one of these as a "rushing water sound" when you rev the engine - but nbt always. Unfortunately, the only way to banish them is to empty and slowly refill your coolant system, bleeding as you go.

I reckon it'll be a sticky thermostat - it's not hugely uncommon on the Evos, and these aren't that different, in many ways.

After that then yes, you need to get a sniff test done on the coolant to ensure there are no combustion gasses leaking in. It seems unlikely, though.

Finally - do you have any kind of modifications done : intercooler? Modified front bumper? Undertray? Gearbox cooler (auto)? What condition is your autobox fluid in?

EDIT: Sorry Dave...you posted whilst I was typing.

[Davezj]

that is very unusual to get things typed out quicker than others i must be get better at the typing lark.

it is always good when you ask a question a few people come back with the same answer. more the merrier for my money Steve

[Turbo_Steve]

Without wishing to rain on your words-per-minute parade, I was also very busy with a piece of cheesecake :D

[Nick Mann]

One other random and potentially unlikely solution - if the corrugated vanes are excessively coroded and/or missing from the rad, this can give cooling issues. I have seen it on a couple of cars, but neither was a Mitsubishi, let alone a VR4. In those cases, the car would only overheat if driving at motorway speed for extended periods, or stuck in traffic on a hot dry day.

[Scanny]

the car is a standard 2.4 apart from the K&N air filter which is the straight swap type. nothing else has been done to the car and this problem doesnt always happen. last week i was hitting 100 MPH with no issues. she usually cruises quite happily at 70 to 80 although she does seem to be a bit choked up these days for want of a better phrase. i know the GDI has issues anyway but i suspect the loss of power is possibly the fuel filter or maybe dirt in the fuel system somewhere. under acceleration the power goes then comes back harder than it should before returning to what i would expect. this does happen occasionally but a day or 2 without using the car tends to solve it albeit temorarily. i have been working flat out for the past few weeks so i am using the car every day. she isnt getting the days off that she likes

[Scanny]

i have just carried out some experiments.
climate control turned down to 17 degrees, i can go up to 70 with no problems, from then on the gauge rises as speed does ie 75MPH is a little hotter than 70MPH but we arent talking overheating stage. just slightly higher than normal running temperature.
with the climate control turned up to 32 i can cruise at 80MPH no problem.

i dont think the thermostat is the problem for the simple reason that the gauge stays at normal running temperature at low speeds, in stop/start traffic and sitting stationary.

booting it isnt causing problems either which to me suggests that engine speed is not causing the issues although admittedly i dont sit in 2nd gear at 3000+ RPM as i normally would in 5th on the motorway

again, this is not an overheating issue. the needle doesnt shoot up to anywhere near the red. it simply creeps up with motorway speeds. 80MPH is roughly an 8th higher than half way where it normally sits

[Turbo_Steve]

Well, it's either going to be cavitation, air-lock or an aerodynamic issue.

As above - do you have any mods fitted? Front bumper? Intercooler?

[scott.mohekey]

Intercooler?

On a non turbo GDI? /pan

[Turbo_Steve]

Ooops! Didn't spot that - sorry.

[Scanny]

other than the air filter it is completely standard Steve and that is a straight swap panel filter with no alterations to the air box and pipes