Overheated once and baffled?

[blue2]

Hi, my car overheated last week after a 340 mile drive, we were in a hot traffic jam near Dover and the temp raised right up to hot for a few mins until I pulled over and switched off. Ive ruled out the thermostat for this reason and also because the heaters are running hot air.
However immediatly after switching the engine off I checked the radiator and it was luke warm even cool to the touch which wasnt right. I waited for it to cool and checked the coolant levels and they were fine. My radiator is only 6 months old so Im pretty certain its not sludged up as I flushed it through when I fitted it with the old 2 litre engine in.

The new engine is tip top and the overheating is nothing swap related, im thinking it may have been casued by an air lock or a dodgy fan or possibly an overworked water pump.

Its not happened since and I was in a four hour traffic jam in 30 degree heat last week so if it was going to overheat again it would have done so then. Ive also been reving the engine upto 2k when stationary for any length of time just in case its the coolant that needs a bit of a push to get round the system.

This has me pretty confused so any ideas on what could have caused it or anything I may have missed checking would be much appreciated. Im in the process of checking the fan now and it looks ok. Thanks

[Barronmr]

Hi,

what engine is in and which model of mr2?

[frisp]

Cooling fan not cut in?

[OlberJ]

as per your call with Woodsy Dan, the coolant system needs to be purged we reckon if you're sitting still for ages, hence the revving you're doing when sitting still.

Basically the thermostat's seem to be a shit design, and they would explain all these Camry's with blown HG's.

You can gut the thermostat and then you'll have warm coolant running round constantly, will take you another couple of miles to get the coolant up to temp on first driving it but you won't get it sticking and boiling your coolant in the engine.

This only seems to be a problem when the car is sitting in traffic or parked up, under normal driving they are fine so i reckon it's nowt to worry about. :thumbsup:

[OlberJ]

Cooling fan not cut in?

The radiator is all the way at the other end of the car on the radiator, so if that doesn't get the hot coolant, then it won't flick the switch and the fans won't come on.

[frisp]

:slap: Posting without thinking. Doh.

[blue2]

Ok thanks, I may try gutting the thermostat then cos reving in traffic is a bit of a pain in the ass. I was convinced it was an air lock. Im going to run it on the drive now for half an hour and double check the fan again and see if the temp goes above half. Thanks

[OlberJ]

There's a possibility it's an airlock, so feel free to do a flush of the system to make sure, but the fact it only did it once under those conditions, points to the non purging type problem.

[blue2]

Ok thanks for the help,ive just been running the engine at idle in the drive for 45 mins. It took about 5 mins for the temp to come up to the usual level just below half way. I had the bonnet up at the front and had removed the plastic trim so I could see and feel the radiator and fan from above and underneath the car.

About 15 mins after the temp came to normal I could feel the radiator start to become warm and then normally hot and after a further 15 mins the fan kicked in for roughly 15 seconds. The fan then proceeded to kick in every 2 mins or so for around 15 seconds each time.

The temp never rose or dropped a bit during the 45 mins, it remained at a constant level just below half way and the engine was always idling (as in a traffic jam) at about 1000rpm.

I did however feel a few drips from the bleed point on the bottom left of the rad but this was when the rad was cold and it stopped when the rad warmed up.

Also Ive checked all the jubilee clips and cant get a turn on any of them. I cant see now how this can be a purging issue because after 45 mins I would have thought this would be enough time see the temp start to rise abnormally due to any stagnant coolant in the engine. Im probably wrong and will do a longer test tommorow for an hour or so.

If this was due to an airlock could it be that the air got out during the overheat? Also I hadnt thought of this but at the time we were facing down hill in traffic,could this have caused the air lock to rear its ugly head?

Im happy it hasnt happened again but Im still stumped doh!

[OlberJ]

Could just be a sticking thermostat then, it's sticking shut and needs a surge of water from the pump to open it.

Sounds daft but they're fickle bastards.

We did sit and talk about this for a fair while after u phoned Dan, hopefully Woodsy or Anth will drop in and throw in their tuppence worth soon.

Although if Woodsy was out on the piss then he may not be able to speak for a few days. lol

[blue2]

Ye I really appreciated the help you and Paul gave as I was really close to cancelling the trip :thumbsup: .
The only thing I dont understand is how the thermostat could have stuck after driving 300 miles, we never stopped for long enough to allow the engine to completely cool, in fact we only stopped twice for a piss break lol . I thought that once the engine was warm and the thermo opened, they stayed open until the engine is stopped and cooled down and then they close. Im assuming they are the standard wax type ones?

Regarding the air lock idea, once the engine had overheated I noticed that the expansion tank was empty, this was when the car was cool. I was thinking that the air bubble could have worked its way round and got to the bottle then sucked all the excess water through into the engine thus filling the gap and getting rid of the air and cooling the engine. Sounds mad but Im clutching at straws:eh:

[OlberJ]

I cannae take credit, it was the other 2 that are the relatively knowledgable ones on the subject. :mrgreen:

That's a fair point about the coolant level so yep, quite possible an air lock.

If you've topped it up and it's fine then i'd let sleeping dogs lie. If it rears it's head again, give the throttle a blip and see if it cures it.

When the thermostat opens it simply becomes flacid ( lol ) enough to let the water past, if the coolant is sitting still, water pump not really moving much, it could stick shut and needs a blast from the water pump to push the thermostat flacid flap ( lol ) open again and let the hot coolant round into the radiator pipes.

Hence the blip of the throttle.

Gutting your thermostat should sort it for u though.

[blue2]

could be down to a flacid thermo then lol Im going to give it a few days to test before gutting the thermostat as I really dont want to have to bleed the whole system, it was a pain in the ass last time. Thanks for the help!!

[blue2]

Just an update, its running fine now, temp doesnt move from just below half way. Im 99.9999% sure now that the overheat was due to an airlock. Gave it a good blast up and down the motorway for a good 2 hours and then some fast hi rev country roads (great fun) and then finally left it on my drive running for over an hour. Fluids have remained constant too.
Checked all hoses and could only manage half a turn on one of them so no leaks either.

[OlberJ]

Glad to know it's sorted. :thumbsup:

Just as a side note, gutting the thermostat's doesn't seem an option now as the darn things run too cool like that, bloody over good Mr2 cooling system lol

[blue2]

Yeah I was a bit apprehensive of doing that, mainly because I use mine as a daily driver and its only a 10 minute drive to work but mostly motorway. I dont really like driving fast when the engine is not up to temp.