The Imp Site

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Head gasket

From: Andy Greenshields
Date: Thu, 4 Mar 1999 11:45:46 -0000
Subject: [imps] Head gasket

Is it possible to have a head gasket go slightly and cause overheating and oil pressure variations without any sign of either oil in the water or water in the oil. I have an engine which seems to be overheating a lot and the oil pressure light comes on from time to time. There are, however, no visible signs of the head gasket having failed apart from the usual non functioning heater.

From: Impmann@aol.com
Date: Thu, 4 Mar 1999 07:37:17 EST
Subject: [imps] Re: Head gasket

Simple answer... yes. If there is a marginal leak off the top of one piston top, water could be being 'super-heated' by the combustion process. There will be a water loss situation, though nowhere near as bad as normal. Thankfully these failures do not usually mean badly warped heads (in fact, I've managed to get away without skimming one that had gone in a similar fashion - that was due to it not being re-torqued in the first place).

I'm not so sure about the oil pressure. It could be that the switch has overheated.....try substituting another one (the one off that engine I sold you should be ok).

It is rare for water to get into the oil (unless it has given way big-styley) as the oil is under a greater pressure than the water, and it does depend upon where the seal has broken.

It sounds to me like a simple fail, somewhere around the back of cylinder three...

From: Andy Greenshields
Date: Thu, 4 Mar 1999 14:04:11 -0000
Subject: [imps] Re: Head gasket

I have just been for a burn in the car in question up the M40 and down the M4. Apart from the fact there was almost no oil in the sump (I put in about 1 litre), it worked OK and the temperature hardly varied despite running at 70mph or more. Therefore the oil must have gone somewhere? Where? There is no visible external leak and upon looking into the radiator there seems to be no oil in the water. On sticking my finger into the neck of the the radiator, there seems to be a thin film of oil on the inside surfaces of the radiator. Is this where the oil has been escaping to? Surely the coolant would show more visible signs of contamination.?

I am puzzled. it would seem to be a problem with the HG but not one I have experienced before. However, a 25 mile high speed run didn't show any faults to me. Is it my friend having satanic influences on Jack or is the HG about to go or has a fault similar to the one you have described.

Date: Thu, 04 Mar 1999 14:30:42 -0000
From: Dave Edge
Subject: [imps] Re: Head gasket

How long is it since this car last ran, perhaps what you are seeing is the oil having made it around all the passageways, oil cooler etc. The only true way to measure oil comsumption is to run a car till warm. Stop on a level surface(both planes) and allow to cool down. Top up oil to top of stick. drive till warm, repark on same level surface. Measure oil level when cold again.

One possible cause of mysterious oil loss is a sticking valve. This means that compression is never acheived on one cylinder, it can in fact suck as the piston falls away drawing oil into the cylinder and out of the exhaust.

Check your plugs and get back to us.

From: Impmann@aol.com
Date: Thu, 4 Mar 1999 09:33:27 EST
Subject: [imps] Re: Head gasket

Hmmmmmmm. OK so no temperature rise.......but oil disappearing. Oily film inside the radiator (but not mayonaise). No visible oil leaks.

Right, a few questions:

1. Any coolant loss?
2. Does the engine sound 'strange'?
3. Was she suggish?
4. Have you still got the oil breather pipe fitted to the carb?

If the answers to questions 1 to 3 are no, then your head gasket should be intact. Certainly blasting along a motorway at over 70 mph for 25 miles should provoke a boil up to end all boil ups.

The oily film in the radiator could be deposits from your anti-freeze solution (especially if it is a bit concentrated) or it could be that a pipe is failing and the deposits are rubber.......

My concern is about the oil breather pipe......take it off when the engine is warm and watch for smoke at tick over, rev the car and let the revs drop... clouds of smoke? Take the oil filler off while the engine is running, is there a large amount of pressure? If there are large clouds of yukk coming from the breather and the backpresure of the engine has increased then the problem is rings based ie you are getting 'blow-by' on the rings (the combustion process is pressurising the sump and you are loosing your oil by it being burnt). On an engine that has done a fair few miles, this oil loss is common on hard motorway driving.......

Why do you think that the HG has gone? If the car is not overheating, just losing oil, it would not be the HG. The oil would have to go somewhere, and 1 litre of oil would make enough mayonaise for a million Tuna sandwiches:-)

If you don't have any joy and you've got time, you could bring it to me for a second opinion...

From: Andy Greenshields
Date: Thu, 4 Mar 1999 15:11:13 -0000
Subject: [imps] Re: Head gasket

I have lent the car to a friend who needs a car to replace her dead Renault 5 (funnily enough it died due to Head Gasket failure). The reason that she stopped this morning was that the car was overheating and the oil light was coming on. I have filled up the oil and the pressure is now OK. I have an oil pressure gauge in the car and the pressure is just over 50 psi when running. Something that would seem normal to me. There has been some coolant loss, but only when the car has got hot. Not having been in the car, I do not know how much. As I have said, the car ran fine on the long run I took it on. It is certainly not sluggish and I managed 80 going up the M40 up to the marlow roundabout. (Those who have visited Mr Anderson will know that this is a killer hill for weak engines).

There is no breather pipe on to the carb but just a tube to the atmosphere.
It seems normal to me. I have not noticed clouds of smoke coming from either this or the exhaust when running. I don't think that there is a dropped valve, though I might be wrong. There is no sign of blue smoke in the exhaust.

The engine is a 40,000 mile unit recovered by from my mothballed Chamois Coupe. It sound excellent and is the quietest engine I have ever had. I had never noticed any oil loss before.

I am convince that my friend Abby is excerpting supernatural forces over the car and that it will go the same way as her Renault. I have never had any problems with the engine in question.

I don't think i am any nearer the problem (if there is one). All I know is that oil has dissappeared ant the engine overheated this morning.

From: Impmann@aol.com
Date: Thu, 4 Mar 1999 12:00:18 EST
Subject: [imps] Re: Head gasket

This is an odd one... if it didn't overheat with you razzing the doo-dahs of it on the motorway, and the oil pressure is fine (50 psi = fine), it's got me slightly stumped.

I don't think that the HG has gone... it really would have boiled after that treatment if it had...

The only other thing to check is the crankshaft oil seal....if this starts to leak it can throw the oil out as a thin film.

I've just had a brainstorm... you say that your heater isn't working. That means it could be full of air. If that shifted, it could have sent an air lock into the cooling system and this caused the overheat. Once the car had cooled down, the airlock could have moved again, possibly being belched out of the radiator...

Another thought... how old is the thermostat? If that locks up, game over for the cooling system...

As I say, I think your HG is intact...