940 compression test
 

Hello, I have done compression test on my 940 2 LTR normally aspirated engine.

No 1 120 psi

2 to 4 150 psi

Would you say this is acceptable?

My tester gauge won't hold pressure, at first thought this might be an engine problem but, on reflection... I think it's the tester developed a fault. Any thoughts please?

I will try it on another car.

The reason for the test is... water coming from the header tank, (losing coolant.)

missing till warmed up and, down on power, although, the 2ltr has never seemed that powerful.

I'm suspecting head gasket on the way out. I does start ok BTW.

Any input gratefully received.. Ken.

I would say 120psi is a bit low compared to the other 3 cylinders, should be no more than 10 percent variation between the highest and lowest readings.
Usual trick is a drop of oil in each cylinder then test again, this will show up worn bores or rings.
You may be right about head gasket...

update
 

Quick update..... I found a broken jubilee clip on the top hose, the coolant dripped out once warmed up; so, that is the cause of my recent big coolant lose but, coolant does ooze out of the filler cap, has done for a couple of years. I don't do more than a few hundred miles a year I should mention.

Regards Ken.

That's good news, if it's running okay I shouldn't worry too much about the head gasket now

How old is the expansion tank cap? Does it need replacing?
Any excess coolant should return to the radiator via the overflow hose.
How full is your expansion tank normally? I have a mark halfway up the wall of the tank. I rarely need to top it up but when I do I never fill past that mark.

filler cap
 

The cap is the original 1992 as far as I know, I was wondering if it could be suspect.

I cleaned out some sludge from the tank and looked at the 2 poppet valves in the cap; were a bit brown with rusty water but seemed to work.

Are they prone to fail?

I keep the level at the max mark or just below.

thanks for reply Ken

You almost certainly need a new expansion tank cap! :err:

Yes, they are prone to failure.

That level is too high! :eek: Should be on the "MIN" mark or just above when cold, the big clue is in the name of "expansion tank" - it allows the coolant to expand and get to the "MAX" mark when hot. Over that and it will escape via the easiesst route which could well be the cap.

Try a new cap, get some new Jubilee clips and any others you find weeping, renew them. Given the B200 is known to be prone to piston slap on #4 cylinder if there are no other coolant losses after renwing the cap and the hoses/Jubilee clips, i'd accept it as the car getting older. As someone else mentioned, dropping some engine oil into the cylinder (via the spark plug hole) and repeating the test will confirm if the rings are worn.

Just to confirm, when you did the compression test, did you pull the fuel pump fuses and open the throttle wide for each test? :thinking:

compression test
 

Thank you for the info,

if it's just my cap that is good news. I let the water level go so low it is just visible and still it comes out of the cap.

I didn't pull any fuses, no. I smelt the fuel during the test but didn't look for the correct procedure.

As my gauge didn't hold pressure it was difficult to see the exact pressures.

I wonder what the pressure was with a new engine because; as I mentioned, "the tank" seems under powered. My 145 I seem to recall was a lot more sprightly, the 940 is probably a heavier car, I've owned it since 2005 and it has always felt sluggish till it's up to 45mph plus.

Many thanks for help Ken.

Letting the level go too low can cause airlocks which expand when hot and push the coolant out of the cap. One of those "damned if you do, damned if you don't" situations.

There's a very good reason for pulling the fuel pump fuses (#11 & #13) and besides the obvious fire risk from the fuel vapour floating around, the fuel that is injected will cause "fuel wash" in the cylinders. As #4 was probably the last one you got to, not only would it have had the most time to get fuel wash but there was probably a longer time between doing #3 and #4 than any of the others because #4 is awkward to get to. This would just add to the effect.

I'd suggest buying a new compression tester and repeating the compression test. This time pull fuses #11 & #13 to prevent fuel wash. Volvo quote the B200F as being 0.9MPa which is 130psi.

https://www.ebay.co.uk/itm/200779373166

That should do the job and because it holds the pressure reading, much easier to read and to use, once screwed in to each cylinder means you can get in, floor the throttle and then crank. What isn't clear in the photos is there is a pin on the side of the "neck" of the tester that you press to release the pressure after each test, you can just make it out in the photos. That holds the pressure until you release it.

As for the 945 being more sluggish than a 145, the 145 with B20A was only ~82bhp if memory serves and weighed ~1200kg. The 945 with B200F is ~112bhp and weighs 13-1400kg so yes, it's heavier and i suspect has higher gearing. Max torque on the B200F is 158Nm which is ~120lbft@2800rpm, i can't remember the torque figures for the B20A (assuming that's what you had, if you had a 145E with the B20E engine then that had 135bhp and was much livelier!) but either way the 945 with B200F wouldn't be much different to the 145 with the B20A - definitely underpowered in such a heavy body!

You could live with it, but coolant leaks will lead to longer term problems with head corrosion and/or radiator corrosion.

I just replaced my HG for the same low compression. My old gauge was pretty poor too, just get a new one they are dirt cheap.

Turned out there was a dent in the metal ring a gasket, I might have dropped the edge of the head on it during the last assembly (done as part of a full restoration).

It did start ok, but ran badly for about 30s, and did seem down on power.