Hi All,

The head on my 93 940 turbo has been removed for the third time. On the previous occasions I assisted my neighbour. He is away at the moment so I'm tackling the job without his assistance.My knowledge is limited.

It has travelled 450000 non city kms (280000k miles).

The first gasket was replaced at 200000kms due to an external coolant leak above the 4th spark plug. The second replacement was due to a coolant leak into the oil. This replacement, is once again ,due to coolant leaking above the 4th spark plug.

The car has been meticulously maintained. Synthetic oil and Mann filters every 8000km & 50:50 coolant mix from concentrate and demineralised water at specified intervals etc.

It has never overheated. Thanks to John Sargent for his invaluable assistance in the fitting of a low coolant sensor.

No electrolysis has ever been evident.

Three head gaskets replaced, but the water pump is the original. It has a small leak so I will change it this time. I'd prefer it to have been one head gasket and three water pumps. I guess you can't win them all.

The car has a sequential LPG system fitted. The LPG does not effect it's performance and is generally used due to it being cheaper.

I will attempt to submit 5 images of the head the block and the gasket. They are loaded to the gallery. Not sure how to attach them.







Image 4 shows where coolant leaked between coolant inlets to the outside.

My Observations.
The brown stains show no evidence of pitting.
There seems to be oil under the gasket on the exhaust side but not the inlet. Is this normal ?
Is the pitting on the valves normal for the kms?

Your thoughts will be greatly appreciated. Thank you in advance.

Hibbo.
NB The 6th image is not mine. Not sure how it got there !

you mention 3 head gaskets and the head has been machined twice? or 3 times?

have you had the head checked for adequate height within spec?

2 skimmings would be expected to take may at a minimum 0.005" per skim

the is a limited amount you can take off before the head is to short in height and effects the cam and timing.

https://www.matthewsvolvosite.com/forums/download/file.php?id=32361&sid=53f553f9e2244f7d9b748237b2a4c88e&mode=view

you may be using a sub standard close to out of spec or out of spec head.

You have checked the head and the block surface for any irregularity from being plane?

Randy

Hi Randy, Thanks for your interest.

On the two previous occasions the head was machined.

I have cleaned the head today and will do the block tomorrow and check for level.

I have had the car for near on 20 years. Prior to my purchase it had been exclusively serviced at a Volvo dealer. Three head gaskets is not good for a car that has been so well looked after. It has had no other problems. The turbo and transmission are original and as new.

I have been using good quality, longlife coolant concentrate mixed to a 50:50 ratio with demineralised water. I'm wondering if I should have diluted it to 30%. It has been changed at 2 year intervals even though the coolant manufacturer suggest 5 years.

No sign of electrolysis has been evident and it has never been overheated.

The centre valves have a different appearance to the outside ones. I thought they may have been pitted, however a closer look today suggest they will clean up ok. Could this be due to the use of LPG ?

Thanks for all help.

Kind regards, Hibbo Australia

I think compression can be higher with LPG. I have a couple John Deere 2-cylinder tractors (1959 630s) and to get similar power as with gas, the LPG tractors had high dome pistons. They also had high altitude pistons which didn't have quite as high dome as the LPG piston but higher domes than the gas pistons that were in high altitude places like Colorado. So, with your 940, you shouldn't have any pinging and damage to the engine. I have alway heard that engines last longer running LPG.
But, I guess that doesn't address the short lived head gaskets. I assume you are not running low octane gas?
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Mine:3-940s running, 1-740, 2-940 parts, dtrs:4-940s running

To me, pitting may indicate preignition.

Does the car still have a knock sensor system?

The only reference that I have found in the numerous manuals that I have was in a Chilton manual that says in a '90 740 - the first thing that happens when a knock is sensed is the addition of extra fuel to cool the combustion chamber.

Changing the timing comes later because that when a knock is sensed, the ignition is happening before a spark is sent - hence changing the timing will not solve the immediate problem.

Perhaps your engine is being damaged by preignition.

If you talk to an expert on your system, a thicker head gasket or a spacer plate might be in order to reduce compression.

Also, perhaps the timing should be retarded.

Since your car is a turbo, I do not think that performance would be reduced a great deal.

An accurate, responsive temperature gauge might be a good idea, as Volvo's gauge is dampened quite a bit. Most modern cars have poor temperature gauges - I was astounded to see how much the temp gauge moves around in my 544.

Hi James,
Thanks for your response.

It does have a knock sensor.

My current thinking is to do with the LPG. LPG does not have the lubricating quality of petrol and I believe runs hotter. To compensate, I use an upper cylinder lubricant and cooler NGK spark plugs. There have been times when that lubricant has run out. I need to be more fastidious in monitoring.

I will do some cleaning today and check for level.The head has been skimmed twice. I will only have it skimmed again if absolutely necessary.

Kind regards, John.