Happy new year everybody.
I\'ve lost half a litre of coolant in the last 2000 miles from somewhere. So I did a compression test, and all cylinders come up 160psi, within 2 psi. It\'s a mk2 Golf Gti 8v.
Can anyone tell me whether the head gasket looks sound from this, and I should look for the leak elsewhere - or that it ain\'t necessarily so?
Cheers
Rob F
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You can't tell, if coolant is leaking into the combustion chamber on the down stroke, it will not affect the compresion, and once the coolant system is pressurised, there will be little loss of exhaust gas into it, as the difference in pressure is minimal.
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I agree with ST. That's an excellent compression pressure balance between the cylinders but I don't think it necessarily eliminates the head gasket as the cause of a leak. In fact the coolant could be slowly but continuously leaking after engine switch-off.
However there could be a much less serious reason for the coolant loss and I would take a very careful look at all other possible leak points before blaming the head gasket. If it still looks as though the head gasket may be at fault, a trip to a garage for a coolant system gas-detector test could be a good move.
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I'd second the previous two responses. Another way of finding your leak might be to treat your Golf to a coolant change, topping up with a fresh antifreeze mixture. You may find that the new coolant "seeks" out the leak for you...
My Mk 2 Golf GTI was plagued with coolant leaks. It worked through most of its hoses over a 20000 mile period until the head gasket finally blew. The most fun leak / blow was of the metal pipe running down and across the front of the block. It had rusted a pinhole in the rear of it, so looked sound but leaked beautifully!
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OK here goes. Firstly remove all the plugs, is one of the plugs stoplessly clean. If so then this cylinder is using water and steam cleaning the pot. If you solder a small 12 volt bulb to the end of 1M of wire and insert down into the cylinder and look in you will see a super clean piston top. Turn engine to half stoke position. If all the same this is not the prob. either the rad is weeping or the steel pipe at the rear of the engine has corroded, or the pump is leaking. So after a 5 mile run from cold does the water level in the header tank drop ?? and when you carefully and slowly release the cap does the level rise. If so then the gasket is away. If not then the leak is elseware. Small rad leaks are difficult to fine as the evaporation rate can be quicker then the leak rate, you need to pressurise the system to 10/15 psi for an hour to see if the rad has a damp patch. I have a spare cap with a car rim trye valve fitted to it so I can pressurise the system. Come Back with information. Regards Peter
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The slight water leak in my mk2 Golf turned out to be the heater matrix, which was also causing internal windscreen misting. This I cured with Radweld, but the matrix was later replaced under the VW heater recall.
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Hey Peter..I like your idea of soldering a small auto bulb onto a bit of wire.......I'll do that next time!
Agreed, looking at the piston crowns & spark plugs will tell you a whole lot about the engine's condition.
--
groups.msn.com/honestjohn - Pictures say a thousand words.....
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The old SUN diagnostic centre had a useful piece of kit, just a pressure gauge connected to an air line and a pipe with a spark plug thread on the end of it. Warm the engine up, whip the plugs out, screw in the plug adapter, get the cylinder being tested at TDC firing stroke, connect the air supply. Leaky valves could be found by listening to carb or exhaust pipe. Worn bores etc, showed up when the oil filler cap was removed. A leaky head gasket showed up as bubbles or overflowing from the radiator.
For my 'field' work I cut and brazed a few bits and pieces, including a couple of radiator caps and pumped the spare up to 70psi. Connected to the spare using a brass valve extender (lorry type). The high pressure was good for checking engines, then let the tyre down to about 15psi for checking cooling sysems. It worked well and saved a lot of guesswork.
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Chemical analysis of the gasses present in the cooling system will show up a slight head gasket problem long before a pressure test, or compression test, does so. Even, in fact, before a cylinder starts to become "steam-cleaned".
The reson is the pressure in the cylinder in vastly greater during the combustion process than the pressure in the cooling sustem. Combustion gasses are then forced into the coolant, but only a very small volume of coolant may escape back into the cylinder when the engine is switched off.
The test involves drawing gasses from the coolant expansion tank into a container filled with a colured fluid (usually blue). Carbon Monoxide (a product of combustion) will turn the fluid green/yellow. The test is known in the trade as "cylinder block combustion test" or simply "block test". Kit may be expensive for one-off use, so suggest you try getting locla garage or mechanic to do this test for you.
Regards, Adam
Whatever is rightly done, however humble, is noble.
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