Ray_Singh

My 1986 951 is using coolant.
When i bought the car, i was told that one cylinder had slightly less compression than the others - i was never told any numbers though.

I have recently noticed that the car is using coolant. I will have to top the coolant level up every so often.

There is no mayo (oil/water mix) on the oil filler cap or in the oil and the coolant is still nice and blue.

Any ideas?

elargentino

In this case, you have 2 possible culprits:
-you have a leak in the cooling system, this is very likely given the complexity of the 951 system.
-you have a slight headgasket weep which is allowing coolant into #4 (most likely) off boost on the intake stroke (vacuum).

Have any white smoke when you sit in the driveway at idle?

Ray_Singh

No white smoke that i have noticed.
I will check and get back to you.....

jerome951

I'd suggest pulling the spark plugs if you don't see a noticeable leak. Coolant seeping into a cylinder will steam clean the plug. If you see this, it's time to replace the headgasket.

Tedro951

Pressure tester, then combustion gas tester. You'll have an answer very quickly.

User 52121

Ditto.

I see you're in the UK, not sure if Harbor Freight has any stores or will ship there, but I picked up a pressure tester kit for under $100 and it's come in handy a few times now (once with the Porsche, twice with my VW.)

Pressurize the system and then look for leaks.

Ronin-951

I had a slight leak that never made it to the ground, no traces, turned out to be the heater hose at firewall...whew!

kbower

I would check the heater control valve and the hoses at the back of the head.
The water pump can also seep out of the weep hole in the bottom of the pump.
If the heater core is seeping you should get a sweet smell as the heater core warms up. Or the head gasket could have a small leak when cold and seals as the engine heats up. I hope this helps... Good luck

Willard Bridgham 3

How's the reservoir cap?.....Working?

Tom M'Guinn

I'd start by pressure testing the cooling system using a tester like the one available at Sears. Some small leaks are impossible to detect without a pressure tester. Hopefully that's all it is. If the pressure tester reveals no leaks, then put the overflow tube into a plastic bottle and see if you are spitting up coolant after driving the car hard. If it spits up after driving on boost hard, but not after tooling around town, then it's probably the head gasket.

George D

When on boost do you see a H20 heat spike on your water temp readings? Excess pressure out of the expansion tank is usually, as Tom stated, a head gasket leak issue. Either get a pressure tester, or take your car to any good radiator shop and let them do a pressure test. You will see any leaks, and if there are none, it's exhaust pressure leaking into your coolant system. This is a HG failure.