Ongoing Temperature Woes

[chrislane]

Some of you will remember that my car decided to get rid of all of its coolant whilst on track at the beginning of april. Despite this, and running with very inconsistent temperatures since (88 one minute, 108 the next, then creeping up to 113), it has shown none of the other telltale signs of hgf - no oil in the water or vice versa, no issues with the way it drives, just a temp guage which is all over the place.

 

Since then i have tried a number of things as suggested by Gav - changing the coolant tank cap, checking the rad is working as it should, coolant is circulating etc. Having run out of the ideas he cold describe down the phone to a mechanical numpty, i finally took it over to burton on saturday. Gav is still pretty skeptical that it is the head, so the next thing to try was checking the sensor for the stack was saying the same temp as the sensor on the ecu - it was. So he decided to change the thermastat. The old one was looking a little worse for wear when he took it off so we hoped that would solve it. By draining the coolant from the system in the process we also ruled out air being stuck in the system.

 

Initially i thought the new thermastat had solved it. The car is running a bit cooler in general. But then i took it out last night and warmed it up pretty steadily. It was fine whilst i kept it below 5k revs (temp guage was high 70s, low 80s at this stage). Steadily upped the pace to 5.5k revs and it was running high 80s - still ok. Running between 5.5k and 6k for a bit and the temp started creeping up (especially when going a bit slower through villages) but it would come back down again. Whenever i went over 6k though it would quickly rise to 106, 108, 112, 113 etc. Backing right off, stopping or switching off completely and the temp would quickly come back down. And if i kept the revs at 5-6k it stayed down. Checked this morning and it hasn't lost any coolant since gav filled it up on saturday.

 

So i dont really know what to do now. Gav thinks the next step would be to take the head off and get it tested, but he still isn't sure it is that in the absense of any other symptoms. I think i'm going to keep driving it and just keep an eye on it in the short term and see what it does.

 

Any other ideas from anyone?

[DeanB]

I know very little about these things as you know but could a dodgy water pump cause this? By not pumping enough coolant?

[Martin R]

Its still a blow across the firering unfortunately IMO. When you take the head off i will be very surprised if there is not a slight indent. What happens with the temp dodging about is the following IMO. The pressure cap releases at a certain pressure. I have a feeling its 3 bar?

 

As the pressure builds up the cap releases the excess and the temp shoots up as the pressure lowers it reseals and the temp drops. Water as you know boils at 100 degrees C. Not much use in a car at times. Pressurizing the system increases the boiling point of the water. The cap releasing causes the water to boil. All IMO and i might be wrong.

 

Edit, do you have a black line around the normal coolant level in the coolant tank?

 

Another edit, have you tried getting it warm and releasing the cap about 3 hours later? If you do what happens?

 

Another edit edit A pic of a blow across the firering. Its on the right hand combustion chamber and runs from about 3 o'clock to 8 o'clock. Its probably only about 2 or 3 thou deep but its enough and you can easily feel it with a finger nail. Not that easy to see in a pic though.

 

 

Good luck.

[Alex B]

Start saving money ready for the inevitable, but in the mean time keep driving it?

[olliecast]

If you keep driving you risk softening or indenting further imo.

 

exactly the same symptoms as mine was when it went. The temperature fluctuation is the exhauat gasses going past the sensor and or heating the coolant.

 

 

[smithpaulg]

Chris

 

Based on everything you have described here, and everything we have discussed previously, I have to agree with Martin.

 

I travelled from Hethel on the motorway in convey with Eddie with mine at a steady 85 all the way (Eddie i still owe you that breakfast) yet as soon as it was put underload off the steady state it had on the motorway the temperature fluctuated as you described.

 

Time to get the head off and get it sorted

 

Paul

 

 

[lummo]

 

Another edit, have you tried getting it warm and releasing the cap about 3 hours later? If you do what happens?

 

 

Martin - what would you expect to happen if you do this? Should the pressure have dropped back down (no hiss when you release the cap) or should the pressure have been maintained (hiss)?

[Martin R]

If you have a blow across the firering the pressure will have been maintained. It will hiss loudly and / or water will come rushing back into the coolant bottle. If all is well there should be little or no pressure in the system when it has cooled for about 3 or 4 hours.

[lummo]

And is this fixable, or is the head scrap if the firering is indented?

[Martin R]

A peen and a skim and a hardness check will determine that. However a peen and a skim and a MLS gasket will probably protect it from another indent? Depends how much the head is worth i suppose and if you have to pay for the spannering.

[chrislane]

If you have a blow across the firering the pressure will have been maintained. It will hiss loudly and / or water will come rushing back into the coolant bottle. If all is well there should be little or no pressure in the system when it has cooled for about 3 or 4 hours.

 

There is no pressure after 3 hours martin. Sounds positive? Although still in the dark as to what is wrong with it.

 

Also no black ring on the coolant bottle - is that good or bad?

[Martin R]

No Black line is good. Chris i can only pass on my experiences. Mine got to a stage where i could not rev it anything above normal and the temp would dodge all over the place. As i do the odd trackday i had to get to the bottom of it and an indent was what was found. I hope yours is less serious but im struggling for another cause. I hope i am proved wrong.

[chrislane]

Thanks martin. All your advice is much appreciated.

 

I am also getting a bit frustrated as i'm really keen to do another trackday soon, but i dont want to waste a load of money booking on to one if i'm worried that as soon as i get the revs up slightly the car will call time on the day.

[DeanB]

If it were me I would have Gav take the head off before doing another track day. You can't properly enjoy the car until it is sorted. You know it will overheat on track and so you will be stressing waiting for it to happen and worrying about causing collateral damage.

The only way of knowing for sure if the head gasket is damaged is to have a look at it. And whatever it is, it ain't gonna fix itself.....

I think Marin is probably right.....I wish he weren't, but........

[russelld]

What Dean & Martin have said is sound advice. You need to get it sorted Chris so you can enjoy the car again.