Temp Guage problem

A bit of a strange one this. Was driving back home last night from a long trip and stopped off at the services on the way. On the way to the services the engine temp gauge was reading half way like it would normally.

When returning to the car after visiting the services i put the key in the ignition and turned it to the first click for the electrics and noticed that the engine temp guage was up near the top. I turned on the engine and the needle then went back down to the middle again.

Turned the engine off and turned the key first click again and it was at half way.

Drove off and stopped at the next services whilst keeping an eye on the temp guage on the way down. Was at half way on the way down. Turned off the engine and turned it back to the first click and it went to near the top again. Turned on engine and went to half way.

Finally got back home and tried again but this time it stayed at half way. Very strange.

Any suggestions guys?

Could it be a dodgy thermostat?

First: check your coolant level and check for airlocks.

I think it's normal for the engine temperature to rise a bit when the car stops, because you've lost the cooling effect of the airflow. However, this effect shouldn't be noticable on the temperature gauge, certainly not to the extent that you've described. My guess is that your cooling system isn't working 100% and thus relies on the airflow of the car moving along.

Does the radiator fan work properly? (should be spinning whenever the engine is running)

Carefully (without burning yourself) check if the radiator is hot top and bottom.

It's possible that the thermostat is not opening fully.

Just an electrical glitch if you ask me, my last Supra used to do the same thing but with the petrol guage, I'd turn the ignition on and it'd come up as a full tank then once started it dropped to the correct level.

Just an electrical glitch if you ask me, my last Supra used to do the same thing but with the petrol guage, I'd turn the ignition on and it'd come up as a full tank then once started it dropped to the correct level.

That must have been fun to think you had a full tank

checked the coolant levels and just topped it up. It was empty in the expansion tank though and has been standing over night. Is this normal? Also i noticed that when i topped it up it seemed a bit brown in colour but maybe this is normal if it has been there for a while?

The fan is working fine so dont think it is anything to do with that.

How would i check for an airlock? Not too sure what one is to be fair or how it would affect it.

Would it be worth taking the car to a garage to get a pressure test to make sure there are no leaks?

Also is there any tests i could do to make sure that the thermostat isnt faulty?

cheers for your replies

checked the coolant levels and just topped it up. It was empty in the expansion tank though and has been standing over night. Is this normal?

There are max & min levels on the expansion tank. Min is where the level should be when cold. Note that filling the expansion tank won't necessarily fill the radiator/cooling system; as the engine heats up the coolant is pushed and pulled about a fair bit (into & out of the expansion tank), sat stationary with the engine turned off it doesn't. If the car is completely cold, remove the radiator cap and see if the radiator is brimmed. DO NOT do this after running the car as the coolant will be VERY HOT and UNDER PRESSURE.

How would i check for an airlock? Not too sure what one is to be fair or how it would affect it.

With the expansion tank closed (and the rad cap on), squish the two pipes at the top and rear of the engine bay on the passenger side. If they collapse easily they are full of air, if they hold firm they probably aren't. When the car is up to temp, does the cabin heater get nice and toasty?

Think i might have to take it to a garage to get it looked at just to be on the safe side.

I will give the things you guys said a try later when i finish work to see if there is anything obvious that i can see.

As for the coolant in the expansion tank it was empty when i checked but i filled it up about 6 weeks ago because it was empty then too.

Seems there may be a leak of some kind and might be worth getting a pressure test done i think.

Hopefully nothing major wrong

Sounds like it is losing coolant, but that could be as simple as a leaking radiator. Look for the simple stuff before you pay someone and/or fear the worst.

To be fair i dont really know what to look for on that side of things. I will look for anything obvious but im not 100% what to look at.

Dont suppose anyone in the area could come down?

Im down at high wycombe at the moment

To be fair i dont really know what to look for on that side of things. I will look for anything obvious but im not 100% what to look at.

Dont suppose anyone in the area could come down?

 

Im down at high wycombe at the moment

Look at your radiator and see if any areas of it look damp (or a different colour, when the rest of is is dry/uniform colour.

After you have driven somewhere and got it up to temp then parked up and it has stood stationary for 15 or so minutes, look for puddles under the car (on a dry day!).

Look at your radiator and see if any areas of it look damp (or a different colour, when the rest of is is dry/uniform colour.

 

After you have driven somewhere and got it up to temp then parked up and it has stood stationary for 15 or so minutes, look for puddles under the car (on a dry day!).

Ok just took the car out for a quick run. Checked the levels of coolant in the expansion tank before going and it was empty when the car was cold. Took the car out for 10 mins making sure i got the engine warmed up nicely.

Parked up and left it sitting there for about 10-15 mins.

I noticed that there was a leak next to the front left hand wheel which upon closer inspection looked like it was coming from the overflow pipe coming from the expansion tank.

Now i thought that was for if the expansion tank was filling up too much but when i looked into the expansion tank it was still empty.

Is this right?

One thing i need to point out though is that the expansion tank is not the original one with min and max lines on it. It is an alloy tank. Not sure if this has any bearing on why this is happening but worth mentioning. Checked for any leaks from the actual tank itself and it seems fine. The coolant seems to be coming from the overflow pipe.

Any ideas?

Just another thought about it. Even if it was the coolant that was affecting the engine temp. Why would it be showing up as normal on the temp guage then very hot when i got back to the car and turned it the first click?

Mate, as I said before I'm 99% sure this is the same electrical fault I was having with my fuel guage, I doubt very much that there is anything wrong with your cars cooling capabilities as it just wouldn't make sense to heat up to that degree when the engines switched off, then rapidly drop when it's started.

If you want my advice, buy an aftermarket water temp guage and sensor and I bet that'll read spot on.

Just another thought about it. Even if it was the coolant that was affecting the engine temp. Why would it be showing up as normal on the temp guage then very hot when i got back to the car and turned it the first click?

If the car is massively low on coolant then the engine won't have a constant supply of the stuff pumping through it and cooling it down: it'll be spluttering through with air in the gaps.

Water conducts heat 25 times better than air, or put another way, air will only cool the enginer 1/25th as well as water (or coolant).

So, if your coolant system is made up of some coolant but lots of air, I would imagine there will be times when the engine is starting to overheat - obviously with zero coolant the engine would overheat very quickly.

So it stands to [my] reason that the engine temp sensor will sometimes be in very hot air, and sometimes be in coolant: when you switch the engine off the coolant stops flowing, at which point it is likely to be in air rather than coolant, so measuring the higher temp. When you start the car, coolant flushes past and the temp reduces.

This all assumes it's a fast but gradual, rather than instantaneous, change in temp reading, if it's the latter then I agree, it sounds electrical. However, ensuring you have sufficient coolant is still mandatory - to help elimininate one set of issues whilst you track down this fault, but mostly for the health of your engine(!). HTH

Edit: SteveR beat me to it, but I'll leave this post in anyway.

Ok just took the car out for a quick run. Checked the levels of coolant in the expansion tank before going and it was empty when the car was cold. ....

Did you put some water/coolant in the tank before you took it for a run? Apologies if I'm telling you stuff you already know, but never run the car if you can't see any coolant in the expansion tank. If you're lucky there'll still be some coolant in the engine block itself, but running a car on no or nearly no coolant can cause serious engine damage.

One thing i need to point out though is that the expansion tank is not the original one with min and max lines on it. It is an alloy tank. Not sure if this has any bearing on why this is happening but worth mentioning. Checked for any leaks from the actual tank itself and it seems fine. The coolant seems to be coming from the overflow pipe.

I *think* I know the pipe you mean. Are you sure the pipe is connected to the coolant tank? I thought that pipe was a simple drain for rainwater etc that collects in the bodywork or battery tray. You can smell the liquid coming from the pipe to check if it's coolant or not.

The cooling system doesn't have an overflow pipe. It's a pressurised system, and the rad cap also doubles as a safety valve if the pressure gets too high (caused by overfilling, usually).

Just another thought about it. Even if it was the coolant that was affecting the engine temp. Why would it be showing up as normal on the temp guage then very hot when i got back to the car and turned it the first click?

It could be a gauge fault, but I would fix the potential coolant leak first (a very low coolant level might cause the gauge to behave weirdly), and then see how the gauge behaves. I would top the coolant level up (if you have no markings on the alloy tank, just fill it half full). I'd then leave it overnight and inspect the next morning to see if there's any suspicious puddles on the floor. If no puddles, take it for a 5-10 minute spin, park up, check for puddles. Leave engine to cool, then check for puddles. Before you drive it anywhere, it's vital you check there's at least some coolant in the expansion tank. Be very careful checking when the engine is hot: it'll be under pressure (if there's any in there!) and you can scald yourself very badly by opening the expansion tank.

If there are no coolant puddles during any of this *and* you're still losing coolant, then it must be being lost whilst driving. As Steve suggested, look for coloured deposits staining the outside of the radiator, rubber hoses, or engine block.

either you have a leak in the coolant system or a air lock. fill the expansion bottle up and the rad go for a drive get it up to normal temp. park up and put a large rag over the rad cap and turn it to open be carefull doing this.coolant should gush out when it stops top up the rad that should elimanate the air lock.

I really wouldn't take the rad cap off when the engine is hot.

how else can you get the air out of the system. there is a bleed valve somewhere but not sure

how else can you get the air out of the system. there is a bleed valve somewhere but not sure

It is a real PITA to get air out of the Supra's cooling system. However the top of the rad isn't really any higher than the pipe that feed it nor the heater matrix pipes at the back of the engine bay.

Without fitting a bleed valve, I think most people remove one of the heater matrix pipes (engine cold and switched off) and top up there, but putting the pipe back on without losing what you just added is almost impossible. The alternative is to park on a VERY steep hill facing upwards, and with the engine running, squish the rad & heater matrix pipes to try and move the air about so it should find its way to the expansion tank (or rad cap if you're careful). Easiest of all is to have bleed valves installed!

Actually I'm sure I saw soemone on here chopped the bottom off a plastic drinks botte and used that as a header tank by attaching the neck of the bottle to the rad (where the cap usually is) and filling it with coolant. They then started the car from cold and squished the various pipes until no more air appeared. Sorted.

I think what i will do first is replace the radiator cap as that could be a factor in this.

I will fill the expansion tank to about half way and keep an eye on it too.

Someone mentioned that there wasnt an overflow pipe from the expansion tank. I have a pipe coming from the radiator which then comes to where the radiator cap is. The pipe then goes to the expansion tank which has a plastic cap on and a pipe that comes off of this which is just hanging loose to the right of the expansion tank.

I thought this pipe was for when there was too much in the expansion tank. This is where the leak seems to be happening but the expansion tank is empty every time i have looked.

Will see if i can get some pictures if my description is not good enough

I filled the expansion tank about 6 weeks back and it all emptied within a few days. I think it was emptying from that hose coming from the expansion tank then too but thought this might just be normal.

Only really thought it might be something bad since i noticed the engine temp guage the other day.

Im hoping it is just something simple or something i havent done right

I think what i will do first is replace the radiator cap as that could be a factor in this.

 

I will fill the expansion tank to about half way and keep an eye on it too.

Rad caps are cheap (just a few quid), but if it were me I wouldn't bother until you've looked at the other possible causes (e.g. leaks underneath). If the rad cap is not holding pressure, it'll let steam or liquid out when the engine's hot, and you should be able to see it doing this.

Someone mentioned that there wasnt an overflow pipe from the expansion tank. I have a pipe coming from the radiator which then comes to where the radiator cap is. The pipe then goes to the expansion tank which has a plastic cap on and a pipe that comes off of this which is just hanging loose to the right of the expansion tank.

I thought this pipe was for when there was too much in the expansion tank. This is where the leak seems to be happening but the expansion tank is empty every time i have looked.

 

Will see if i can get some pictures if my description is not good enough

Hmm. My supra's tucked up in the garage at the moment, but give me a shout if you get stuck and I'll take a look and maybe photos. The expansion tank cap does have a tube attached, but IIRC it doesn't/ shouldn't vent to the outside, otherwise the system would be incapable of holding pressure: the engine would heat the coolant to just below boiling point (or actually to BP) and the coolant would evaporate/boil off. If you're sure your coolant does vent to outside, then I suspect that's where your problem is.

...I thought this pipe was for when there was too much in the expansion tank. This is where the leak seems to be happening but the expansion tank is empty every time i have looked.

Doesn't sound good. The expansion tank should only overflow (via the tube that goes to open air) when there is either:

- way too much coolant in it (and this is unlikely if you say it is emplty when cold)

- a massively overheating engine (expanding the coolant so much that it has nowhere else to go.

you might be lucky and the rad cap spring is past its best so letting coolant out too easily, but you might be out of luck and have a more serious problem.

I assume your water pump is ok?

I think i will get it checked out at the garage then as im not too good when it comes to things like this.

Probably best to play it safe even if it is something simple. It just seems really strange that this is happening and not anything obvious as to why it is happening

Ok just gave it one more go having a look at it myself to see if i can narrow it down.

Since last using it which was yesterday the coolant in the radiator cap needed topping up slightly and there was no coolant in the expansion tank. There wasnt any in there on the last quick run anyway.

I topped it up to the top of the neck, then i filled the expansion tank to half full then turned on the engine and waited. It got to half way on the temp guage and stayed there. It then started dripping slightly from the tube that hangs out the side of the expansion tank.

Here we go again

I gave it a few revs of the engine and then noticed that the hose was dripping quicker now because of that.

Turned off the engine and it was still dripping a little bit but not as bad as when the engine was on.

Im guessing it must be leaking all over the road when i am driving and obviously emptying the expansion tank. Unfortunately the coolant is not going back into the expansion tank like i thought it was meant to but instead going onto the road. Bugger!

Could it be anything to do with the tube going into the expansion tank?

Why would it be bypassing the expansion tank and going straight out the overflow pipe?