Advice please - Mk1 TT 180bhp head gasket failure??

[PRH]

Daughter's TT roadster overheated last summer. It has been losing coolant since with no obvious sign of leak. Local garage chemical test on coolant and found leak sealant additive and combustion gas in the cooling system. Cylinder no 2 & 4 had P0302 & P0304 fault codes: "cylinder misfire detected".

I have just done a cylinder pressure test and the readings are from left to right are 140psi, 170psi, 160psi & 180psi.

Is the different between these readings indicative of head gasket failure or should I be checking anything else before I start to strip the head down?

Ps it still runs seemingly OK!

 

[Magnet]

Hello Richard,

A couple of important bits of detail to fill in:- 

Why did the car overheat last summer? Overheated to what extent - running time? What if anything, was done to investigate/ sort that problem? 

How much coolant is it currently using in x miles? 

Since the garage has found evidence of leak sealer additive, can we take it that that has not been added during your ownership - which is how long and mileage covered? 

Did the garage carry out a pressure test on the cooling system? 

Compression test results - It appears that the cylinders showing a misfire code are the two with the highest compression pressures - strange! 

140psi is obviously lower than the rest, and may (in caps) be the cylinder into which the coolant is leaking, but...

It would be difficult to clearly confirm HGF at the moment - until there are some answers to the above, but it doesn’t sound good. 

Perhaps you could come back to us, and I should be able to suggest another test which would be useful before dismantling. 

Kind regards, 

Gareth. 

 

[PRH]

HI Gareth

Unfortunately I was not with the car, but son in law, just passed his test, was. It obviously overheated to the extent that the gearbox was affected as he could not change gear until it cooled down. At that point he checked the oil level which was low and put 1l of coolant in. I am guessing but the car is only used at the weekend and he is putting in 1l circa 100-200 miles.

 

The sealer was not added by myself, I used the car from 88k to 90k miles over 1 year with no problems. He had the car last June and has done about 750 miles. The only difference was that he did some longer motorway journeys where the overheating problem first appeared. 

I have attached an image of the report form the garage, there is no mention of a coolant pressure test.

It may be unconnected but I had a 225 roadster and the previous owner had a fault with the oil cooler which contaminated the cooling system, as when I bought is I did a full coolant flush and replacement thermostat/temp switch, but not sure this explains coolant loss.

IMG_5170.HEIC

[Magnet]

Hello Richard,

Thanks for the additional information. My system doesn’t react too well to the attachment, so I’ll pass on that. 

By what you say, it sounds as if this engine has been well on truly toasted, and may have been driven to a point where it even lost (considerable?) power. It would also seem the reason for that overheating was not solved. 

Low on oil? Does it now use any significant amount of oil as well as the coolant? Let’s hope not, but if so, it worth thinking about the worth of simply replacing a head gasket on a now worn engine. 

Now knowing the history, it probably sounds as if it’s hardly worth having the coolant system pressure tested, since its using a significant amount of coolant, but...

Oil cooler contamination? It would be reasonable to expect that If this is the source of the coolant loss, then you would expect to see evidence in the oil, and/or oil in the coolant. 

One simple ‘test’ you could try would be to take the car on a run of at least 10 miles ( having ensured coolant and oil are to the correct levels - and obviously keeping an eye on the temperature gauge). Straight away after, get someone to rev. the engine to 2000rpm and hold it steady for at least 2 minutes, while you observe the exhaust - looking for white or blue smoke. Not a conclusive test but always worth doing. 

Summary:- in view of its history, I would think the overall health of this engine needs assessing before deciding what’s worth doing or not. Of course, this can only be done by actually inspecting the car. 

Kind regards,

Gareth. 

p.s. If you do decide to have the coolant system pressure tested - simple and inexpensive - and fingers and everything else crossed- it turns out to be OK, then it would be worth changing the reservoir cap.