overheating revisited

[MRTWO]

ok so I've read through plenty on here about overheating/coolant bleeding etc, including this and this, but I haven't found anything yet that matches the scenario I have

what I always have is high rpm (around 2000 but constant) on cold start and I know this is normal and I may consider the manual choke option

as the engine is warming is starts to hunt between 1000-2000 and then when its at normal operating temp the rpm is rock solid around 850

I mention all this in case its important because today my temp guage went to just below half, as usual, but after a few minutes it went right off the scale. so I stopped the engine but left the ignition on so I could monitor the guage. after about 4 minutes it returned to the normal position and I could idle the car without the temp rising, but as soon as I drove off it went back up to off the guage.

I have been able to repeat over and over this and I've tried the lazy method of trying to bleed, and I will tomorrow do the standard method...

...but what puzzles me is why the temp can return to normal so quickly when I turn the engine off but then sit at that normal level and not drop further even if I watch it for the next 15-20 mins. This sort of suggests to me (a complete novice) that may be its a guage/sensor problem?

does any of this make sense to anyone?

[kevin..in]

bouncing idle is a symptom of air in the coolant
first thing you need to do is top up and bleed the system
could well be this is all thats wrong, but you need to sort this first

[MRTWO]

thats my plan for tomorrow, but its been doing that since I got the car 2 months ago and *only* during the warm up phase. once its at normal temp it no longer bounces

actually I want to replace the coolant completely as the car came with loads of history, but nothing mentioning if the coolant has ever been done, and the car has just passed 60,000 (and its 21 years old, of course)

although this may well be the cause of the new temp problem, I'm slightly unconvinced as the car has had this behaviour for the last couple of months at least

any other thoughts or things I can check if the bleed doesn't fix it?

btw, I noticed the fan never comes on, even when the temp is off the guage. I've read in other posts that the fan not operating is normal in normal circumstances, but surely it should come on if the coolant is this hot?

[crazybrightman]

could be air in the system still that boils itself out when hot only to return when cold. or a dodgy warm up idle valve, gunk in the coolant system etc.

[kevin..in]

btw, I noticed the fan never comes on, even when the temp is off the guage. I've read in other posts that the fan not operating is normal in normal circumstances, but surely it should come on if the coolant is this hot?

which fan
engine bay or radiator?
in over 4 years I have only ever had the radiator fan come on once
to check engine bay fan is working disconnect the white plug at the temp sensor on the top of the engine it should run constantly with this plug out

[MRTWO]

engine fan. I tested it and the actual fan works but it never comes on even when the temp guage goes off scale, so maybe the switch is faulty but I don't have any jumper wires to test it.

I'm not having much success bleeding either, in fact I think I made it worse!

Also, since this started I noticed the exhaust is showing alot more smoke. It was fairly clean previously and the exhaust itself was new a month ago and has been fine since so I'm wondering if this isn't really all down to the head gasket

I'm really feeling frustratingly out of my depth and think I'll just have to take it to Toyota

[cartledge_uk]

I just noticed your in crawley.

I can pop over and take a look if want?

[MRTWO]

that offer is appreciated and I've PM'd some details.

nice day for it too!
thanks!

[kevin..in]

make yourself a mug of tea in the mug, then put the hot teabag on the sensor it should be hot enough to bring the fan on

[MRTWO]

A H-U-G-E thanks to cartledge_uk for making me less of a newbie and showing me a few things, including how to put some liquid into the radiator! (it was a bit dry when he turned up though it seemed fine this morning)

anyway, I now know how to bleed the coolant system and thats great

nice to meet you mate, and I really appreciate your effort to come along tonight

cheers!