Compression and Leakdown Measurements

[OldBlueVolvo]

Hi all,


My car hasn't been used much in recent years. Lately it has started to smoke from the exhaust and lacks power taking off. I have performed compression and leakdown tests on the hot engine. Here are the results.


Cyl 1: 14 bar. 8% leakage
Cyl 2: 14.4 bar. 10% leakage.
Cyl 3: 14 bar. 63% leakage.
Cyl 4: 14.8 bar. 7% leakage.


Tested at around 100 psi.



The compression seems high on all cylinders but still all within the specified 2 bar of each other. So my guess is carbon build-up. Does that sound about right?

The leakdown test on cylinder 3 shows excessive leakage. I hooked up the air compressor directly to that cylinder, unscrewed the oil cap and saw it dance around. Then did the same on cylinder 1 and the cap didn't move.


No bubbles in the coolant tank and no air heard escaping from the exhaust tail-pipe or carb intake during test.



So I'm thinking that there's excessive blow-by on cylinder 3 and that the engine will need to be sent off for work.


I thought I would post this in case anyone has any comments before I pull the engine, which is quite a big step! I find the cylinder 3 measurements a bit odd, where the compression seems fine but it leaks air past the piston.

[Clan]

Originally Posted by OldBlueVolvo

Hi all,


My car hasn't been used much in recent years. Lately it has started to smoke from the exhaust and lacks power taking off. I have performed compression and leakdown tests on the hot engine. Here are the results.


Cyl 1: 14 bar. 8% leakage
Cyl 2: 14.4 bar. 10% leakage.
Cyl 3: 14 bar. 63% leakage.
Cyl 4: 14.8 bar. 7% leakage.


Tested at around 100 psi.



The compression seems high on all cylinders but still all within the specified 2 bar of each other. So my guess is carbon build-up. Does that sound about right?

The leakdown test on cylinder 3 shows excessive leakage. I hooked up the air compressor directly to that cylinder, unscrewed the oil cap and saw it dance around. Then did the same on cylinder 1 and the cap didn't move.


No bubbles in the coolant tank and no air heard escaping from the exhaust tail-pipe or carb intake during test.



So I'm thinking that there's excessive blow-by on cylinder 3 and that the engine will need to be sent off for work.


I thought I would post this in case anyone has any comments before I pull the engine, which is quite a big step! I find the cylinder 3 measurements a bit odd, where the compression seems fine but it leaks air past the piston.

does it affect the idle smoothness? try taking off cyl 3 plug lead when idling see what difference it makes compared to one of the others...

[Laird Scooby]

Originally Posted by OldBlueVolvo

Hi all,


My car hasn't been used much in recent years. Lately it has started to smoke from the exhaust and lacks power taking off. I have performed compression and leakdown tests on the hot engine. Here are the results.


Cyl 1: 14 bar. 8% leakage
Cyl 2: 14.4 bar. 10% leakage.
Cyl 3: 14 bar. 63% leakage.
Cyl 4: 14.8 bar. 7% leakage.


Tested at around 100 psi.



The compression seems high on all cylinders but still all within the specified 2 bar of each other. So my guess is carbon build-up. Does that sound about right?

The leakdown test on cylinder 3 shows excessive leakage. I hooked up the air compressor directly to that cylinder, unscrewed the oil cap and saw it dance around. Then did the same on cylinder 1 and the cap didn't move.


No bubbles in the coolant tank and no air heard escaping from the exhaust tail-pipe or carb intake during test.



So I'm thinking that there's excessive blow-by on cylinder 3 and that the engine will need to be sent off for work.


I thought I would post this in case anyone has any comments before I pull the engine, which is quite a big step! I find the cylinder 3 measurements a bit odd, where the compression seems fine but it leaks air past the piston.

Try adding 0.5L Carlube ATF-U to the engine oil and driving it. When it's due an oil/filter change, do it as normal and after refitting the sump plug and new filter, first add 0.5L ATF-U to the engine then top up to the correct level with your normal 10W40 semi-synth. My guess from what you've described is that you have sticky piston rings due to lack of use, the ATF-U will help to clean and release the sticky rings while also cleaning the rest of the engine internally and reviving the dry rubber seals to help reduce oil leaks.

Also worth giving the PCV system a good service to ensure that isn't contributing to this.

As Clan said, try removing plug lead #3 (use insulated pliers) to see if it alters the idle - if the leak-down is as bad as the figures suggest then it won't make much difference but will once the ATF-U has freed the piston rings so will once more feel livelier once it's back on all 4 cylinders instead of just three!

[OldBlueVolvo]

I pulled the HT lead from cylinder 3 and the idle speed dropped a bit. But when I pulled #1 the drop was similar.


The dipstick oil doesn't look great so I'll start with the oil change + ATF as suggested and give it a run next weekend.


Also, I unscrewed the oil cap with the engine running and it didn't move at all.


Another thing to note is that the exhaust stops smoking every now and then (it stops for a few seconds at a time).


When tested, the inlet manifold vacuum was steady on the spec value, with a slight drop every few seconds.

[Laird Scooby]

Originally Posted by OldBlueVolvo

I pulled the HT lead from cylinder 3 and the idle speed dropped a bit. But when I pulled #1 the drop was similar.


The dipstick oil doesn't look great so I'll start with the oil change + ATF as suggested and give it a run next weekend.


Also, I unscrewed the oil cap with the engine running and it didn't move at all.


Another thing to note is that the exhaust stops smoking every now and then (it stops for a few seconds at a time).


When tested, the inlet manifold vacuum was steady on the spec value, with a slight drop every few seconds.

I'm wondering if you had a sticky piston ring and it's already starting to free itself. I suspect the run next weekend after the oil/filter change will improve things a lot.

[OldBlueVolvo]

Thank you to both Clan and Laird Scooby. I did an engine flush/change and the car runs much better now. Very little smoke and power is mostly restored.