SLROC Forum

Did a compression test on my 3.5 V8 as its drinking water and oil. 136k miles. Test was done with engine warm, all plugs out. I done each test 3 times and took the average. Results:
Cylinder     Dry           Wet
1              140            139
2              138            152
3              140            150
4              145            153
5              138            145
6              150            162
7              150            153
8              142            153

What should the compression be for this engine? Looking at these I don't see any reason for head gasket blown - can a fault not show up on a compression test?
I was assuming I was going to have to do an engine rebuild this summer but now not sure it's needed?

150 psi is a good figure considering the miles on the engine. if its drinking water and oil then that might be 2 problems that might be unrelated, or (and someone else on here might say) you may have a crack in the block which is a problem the V8's suffer. its still heads off tho and pistons out, you can do this with the engine in but I would pull it. at the miles your engine has on it I would replace it with a known good one then when you have time srtip the old one and find the cause/s recondition it if worth doing and fling it back in. If it is cracks to the bore/block then it will need machining for liners or a new block.
Real Steel do a realy good book to take you thru the strip n rebuild on the V8 and are well respected in the motorsport world for engines and parts.
Give "Rangerovering" on here a shout he sleeps with a couple of V8's most nights 

Thanks F4. Yes I hadn't thought of the dreaded cracked block. That's a good suggestion about using another engine I hadn't thought about that. Have you heard about a head gasket failure that does not show up on a compression test? (this might be wishful thinking but any hope to hold onto for a block that isn't cracked!)

Head gaskets can fail in other places rather than just into the cylinders, it's unusual but a gasket can fail from a water way or oil way and leak out or oil way can leak into a water way or vice versa, unusual but possible. Does the engine smoke excessively and if it does what colour is it? I would suggest coolant system pressure tester, pressurise the cooling system and see if the pressure drops quickly and if it does try and find where the water goes. The other thing is a cylinder leakage test, it involes putting compressed air into each cylinder in turn and watch where it leaks to.With all the plugs, radiator cap removed while being tested, my sugestion would be to do this on a hot engine as sometimes a cracked block might not show up on a cold engine.
Best of luck.
                    Stevie.

I agree with the above, do the free bits/checks first. and yes a head gasket "usualy" goes from a cylinder out as that is where the highest pressure is felt but oil ways and the water jacket have their own local pressures that the gasket has to contain.
Its possible a previous owner has cooked it a bit due to a burst hose etc or its had a head off in the past and a cheap aftermarket gasket was used during the rebuild... do the above checks and the results will head you in the right direction.
Is it a 3.5? on carbs?
Drew.

Thanks for the ideas chaps. I asked around at work to see if anyone had a coolant pressure tester but no luck. Someone had another good idea though. I took the car down to my local MOT station this morning and got them to put the emissions test machine probe in the expansion tank to sniff for exhaust gases. There was absolutely nothing. No reading at all. This combined with my compression test which looked pretty good is making me think I have a coolant leak rather than a head gasket issue . It also rules out a cracked block I think. So I'll keep asking around for a coolant pressure tester (the garage didn't have one either). The engine does not smoke, so I reckon the oil usage is down to leaks from the valley gasket. There was a little white crystal stuff coming from the lower water pump connection. Does this make sense - are my assumptions correct?

how much water and oil is it using?

After a days off road use it needs about 3/4 pint of oil and the expansion tank will be dry so about a couple pints of water.

is the oil and water mixing in the block?

There is no water on the dipstick, but there is a little mayonnaise on the oil filler cap. I've just ordered an oil filter, so next step is to drop the oil and see what comes out. I'm not bothered about having to top it up - more concerned something is wrong with the head gasket. Another thought......if the crank seals are knackered and you go wading I'm assuming water can get into the engine?? If so I think this is likely the source of the mayo on the oil filler cap. Alternatively as it runs exclusively on lpg and this has a higher water content in it??

As the normal working temp of oil is above the boiling point of water then any water that finds its way into the sump will boil off, mayo on the filler is not always a sign of a gasket/water leak, crankcase ventilation lets fresh air (cold moist) into the engine when it cools down of an evening where it condenses onto the cold surfaces it is then boiled off when the engine gets back up to temp, you dont usually see the mayo on an engine that has had regular oil changes but you will see it on high mileage engines or where they have not been kept in good oil or are used for short journeys where they dont get up to temp.
I have a small smearing of mayo under the oil filler cap of my 3.9 disco (none under either rocker cover) which uses no water but uses around a litre of oil between services.
If the crank seals are knackd I would expect them to be leaking a lot of oil, do you have any visible water / oil leaks.
Petrol and lpg are hydrocarbon molecules, made up of hydrogen and carbon. its only when burnt (given oxygen and energy) that they give off carbon dioxide and h2o (water) which is what leaves the exhaust pipe, there is no water in petrol or lpg (or diesel) until after combustion has taken place.
What were the plugs like when you took them out, were they all the same or were 1 or more different to the rest?
Is the engine breather full of oily crud?
Where are you located?
Drew.

Plugs looked good, nice chocolate colour. I'll need to check the breathers - never done them so suspect they'll prob be full of crud. I'm in kirkintilloch.

How are you gettin on with it?

Not had a chance for a serious look, but quick look around the engine and several areas look as if they could have leaks. Radiator looks as if its leaking and the heat pipe connection at the back of the engine looks as if its leaking also. Still trying to find someone with a coolant pressure test kit so I can confirm. Machine mart have a vat free offer on this weekend so I might treat myself to a kit.

So I had a look at coolant pressure testers and they are how much??!!?
Plan B therefore. Make my own.

So I bought some stuff from ebay. A new expansion tank cap, a standard alloy wheel valve and a selection of thicknesses of sheet rubber:



alloy wheel valve:



Drilled a hole through the rivet in the cap and enlarged to fit the alloy valve:



Made a gasket out of the sheet rubber:



Fitted it:



And assembled the valve into the cap:



Blanked off the overflow with the circle cut out of the gasket and a jubilee:



And fitted the cap:



Trusty foot pump used to get 1 bar (15psi) of pressure:



Two leaks found from radiator top hose:









All in this cost less than a tenner