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700/900 Series General Forum for the Volvo 740, 760, 780, 940, 960 & S/V90 cars |
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940 compression testViews : 1028 Replies : 10Users Viewing This Thread : |
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Jun 15th, 2021, 14:11 | #1 |
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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. |
Jun 15th, 2021, 15:44 | #2 |
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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...
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Jun 15th, 2021, 16:00 | #3 | |
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update
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Regards Ken. |
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Jun 15th, 2021, 18:55 | #4 |
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That's good news, if it's running okay I shouldn't worry too much about the head gasket now
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Jun 15th, 2021, 19:25 | #5 | |
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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.
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Jun 15th, 2021, 21:01 | #6 | |
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filler cap
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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 |
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Jun 15th, 2021, 22:30 | #7 | |
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Yes, they are prone to failure. That level is too high! 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?
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Jun 16th, 2021, 09:30 | #8 | |
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compression test
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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. |
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