HC Reading from Cooling System 42ppm means???

[DaveBoettcher]

1988 944S with 158k miles on the clock. I use her every day.

Because oil was getting into the coolant I had the oil cooler gaskets changed in April at the local Porsche specialists I use.

In May I had the coolant temperature switch and a hose changed at a different garage. This second garage noticed that there was some oil residue in the coolant header tank and did a bit of investigating. They said they were getting an HC reading of 18ppm from the coolant filler opening and that this showed a head gasket problem. I didn't take too much notice of this at the time because I thought it must be something to do with the oil cooler problem.

However I have just had the second garage check the reading again and it has gone up to 42ppm. They say this is an early indication that the head gasket is going. I queried whether evaporate from the residual oil in the cooling system could cause the reading, but they said the Crypton equipment they use can distinguish between oil and fuel hydrocarbons.

Anyone got any experience of this? Is head gasket the correct interpretation? It seems weird that both the oil cooler gasket and head gasket should go so close to one another - but then again the car is 21 years old.

If it is the head gasket, what is the likely cause of failure, and how likely is it that the face of the block or head will be damaged? Will I be able to just put in a new gasket, or will the head or block need skimming and how practical is this?

Thanks for any help.

Regards - David

[Techno Duck]

Originally Posted by DaveBoettcher

If it is the head gasket, what is the likely cause of failure, and how likely is it that the face of the block or head will be damaged? Will I be able to just put in a new gasket, or will the head or block need skimming and how practical is this?

Any loss of coolant, rough idle on cold starts, over pressurized coolant system? Any exhaust content in the cooling system is a sure sign of head gasket failure.

As you said, its a 21 year old car and the fiber gasket breaks down over time. Typically the material literally disintegrates and will eventually split the fire ring on the gasket, allowing coolant to enter the cylinders and combustion gasses out.

Usually headasket problems do not result in damage to the block or head unless the car was over heated as a result of head gasket problems, in which case you can be dealing with a warped head. The other possibility is scored cylinder walls from coolant entering the cylinders, but i would not worry about this unless you have been driving around for a long time like this.

The block i would say 99% of the time does not need to be surfaced unless you had an overheat. The head should be checked by a machine shop and decked the minimum amount to make it flat if needed. Otherwise have them clean it up, change the valve guides / stem seals and throw it back on the car. The only potential damage on the cylinder head is possible pitting from corrosion. This is typically a problem if the car was not using phosphate free coolant, or if the coolant was never changed in the cars life. This can either be fixed by decking the surface or if more severe, welding and resurfacing.

Here is a picture of the original headgasket on my n/a, forget the mileage but think it was around 80k miles. You can see the fiber material disintegrated, it was like this in a number of spots, just at this particular spot it allowed coolant to push past the fire ring which eventually split.