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The mkiv Supra Owners Club

Dangerously Overheating!!!


Fitz

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Which of those pics is your new rad cap? If its the one with the spring then that looks right, the other one with the blue part doesn't look right and wouldn't seat in the neck of the rad and wouldn't let the system pressurise(pressurised water boils at a higher temp iirc) therefore it would just boil into the expansion bottle. The one with the blue part looks like it is broken. which would cause your issues. unless its a strange aftermarket radiator.

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Shouldn't the cap have 1.1 bar stamped on it, not 0.9?

 

That was my initial thoughts

 

Which of those pics is your new rad cap? If its the one with the spring then that looks right, the other one with the blue part doesn't look right and wouldn't seat in the neck of the rad and wouldn't let the system pressurise(pressurised water boils at a higher temp iirc) therefore it would just boil into the expansion bottle. The one with the blue part looks like it is broken. which would cause your issues. unless its a strange aftermarket radiator.

 

The new rad cap is the one with the spring in it, the old one is a Blitz Rad cap bought from a trader on here almost 2 years ago. I haven't had any problems with overheating with the new rad cap except recently after the car was parked up for 2 months and not used.

 

The new rad cap 'fits' except it wont press down far enough for the teeth to get under the catch. So if anyone knows the part number for a stock rad cap I would be grateful if you could share.

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The system wants checking with a pressure tester first. Then the cap wants pressure testing. If all is OK renew the thermostat and have the rad checked out, if it only overheats in traffic have the fan's viscous coupling checked out. If it's got that hot it may have done damage to the head :(

 

Can any garage do pressure testing on the coolant system?

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Fitz, have you checked the basics? So often these things are something simple.

 

I would strongly suggest that you run the car stationary until it get up to temp and start playing about with all the pipes.

 

I am betting that you will find a split in 1.

 

I think the high temps are a red herring. The reason for the high temps is that you are running the car once all the coolant has pissed out.

 

Let us know how you get on. (start with the big hose at the front, the the one right at the back connected the the metal pipe)

 

Need to top the rad up to the top and the expansion tank also. Just use water for the time being.

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Fitz, have you checked the basics? So often these things are something simple.

 

I would strongly suggest that you run the car stationary until it get up to temp and start playing about with all the pipes.

 

I am betting that you will find a split in 1.

 

I think the high temps are a red herring. The reason for the high temps is that you are running the car once all the coolant has pissed out.

 

Let us know how you get on. (start with the big hose at the front, the the one right at the back connected the the metal pipe)

 

Need to top the rad up to the top and the expansion tank also. Just use water for the time being.

 

Thanks Pig, I've done the basic checks a few times over to try and establish if there is a leak of some sort. I've been letting the car start from cold and leaving it for about 10-15 mins as it gets to 'normal' operating temperature.

 

I've fiddled with pipes, listened out for hissing noises and looked for leaks, so far nothing.

 

I think I read on an FAQ that the cooling system takes about 9 L of coolant? Is that true? Because if my system went dry after being sat for 2 months I think I'm lacking a few litres.

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So long as the car isn't kept where the temp drops below freezing it's a terrible waste of antifreeze (coolant additive) to be putting it in. Just use ordinary tap water until you find the leak, or problem. It's one of those jobs a good garage should sort in no time, or at lest diagnose.

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Well, it's not the rad cap. I put the new one on on Friday morning and now in sat at the side of the road with an overheated engine a few hundred yards away from the garage.

 

Expansion bottle lid has popped off again and is boiling away after letting coolant out on the inside of the bay (Joyful). Passenger footwell is dry although no heat comes through the heaters, just cold air.

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I'd be thinking about the expansion bottle lid popping off. I can't remember if the expansion bottle is pressurised like the rest of the system. Something is pressurising the expansion bottle (which may or may not be normal depending on the previous sentance), but the build-up of pressure is being released by the expansion bottle, not the rad cap. This is strange.

 

I can think of 2 possibilities:

1) the expansion bottle cap is faulty, and releases pressure, thus causing the collant to boil and therefore loss of coolant.

2) the system is over-pressurising. (seems unlikely though: the rad cap should pop, especialyl a new one, when this happens).

 

There might be other things to check that I can't think of.

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The expansion tank has got a simple overflow pipe that comes out the cap and the cap is only a press

on job not a screw or rad type fitting, if its got hot pressurised coolant going into it very rapidly it

could pop the cap as more is going in than the overflow pipe can cope with

 

If the engine has overheated before then could it have caused a head gasket problem ?

Edited by Dnk (see edit history)
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When I checked the dipstick there was no white substance on it and all looked normal and fine.

 

However, the idle has turned lumpy since the last overheat where steam was pouring out of the car.

 

Damaged internals?

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The expansion tank is there to catch coolant once the system pressure overcomes the rad cap spring. I'm thinking water pump now

 

The water pump has done about 15-20k since it was fitted. I'd hope a brand new OEM water pump would last longer than that. :S

 

It's in with a local garage at the moment having the system pressure tested.

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Worse case senario is head gasket and a warped head, if it is the head gasket i'd have the head checked

to see how flat it is and not just slap a new gasket on there.

 

I'd get it into a decent garage to go through some checks on it now and if it is head gasket

failing it might pay you to find a replacement engine as they appear to be cheap.

 

If the head is warped then it could very well be scrap due to it going soft and

if it needs more than 0.1mm to get the face flat again its in the bin as the cam

journals will be out of true by too much.

Edited by Dnk (see edit history)
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Just got out of the garage now and they've told me that it's the Head Gasket that's failing. They ran a combustion test and 'it came out yellow straight away'.

 

What are my options now then? Source a new engine as Dnk says?

 

This car is going to be the death of me, either stress related or the Mrs. will kill me

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