What to do with leak down and compression test results (2 Viewers)

[rosi6655]

Hey fellas.

I have a 1996 LX450 and I noticed a had to add a tiny bit of coolant over the past 1000 miles. I couldn't find any leaking hoses, and as far as I can tell it has been running fine. I performed a leak down test on each cylinder followed by a compression test. I did the leak down test at 75 psi. Here are the results of that:

C#1 72 psi - radiator level rising/few bubbles, air coming out of oil fill cap
C#2 70 psi - air coming out of oil fill cap
C#3 56 psi - air coming out of oil fill cap
C#4 66 psi - air coming out of oil fill cap
C#5 68 psi - air coming out of oil fill cap
C#6 70 psi - radiator level rising/ few bubbles, air coming out of oil fill cap

During this test I didn't hear any air leaking through the exhaust or intake.

Results of compression test:

C#1 - 190 psi
C#2 - 180 psi
C#3 - 120 psi
C#4 - 185 psi
C#5 - 155 psi
C#6 - 180 psi

These results for sure tell me that I have a small head gasket leak although I have had no coolant in the oil or vice versa. The leak down and compression tests are marginal/bad on a couple of cylinders.

I am not a seasoned mechanic by any stretch, but this is looking like the entire engine needs work. I am looking for any advice and guidance you all may have on the next steps and the best path forward. It is worth noting, I love this truck and I have not noticed any degradation in performance.

 

[Malleus]

All of the plugs had some scaling on them (does that suggest anything in particular?). No noticeable difference between cylinders. I had never taken the plugs out before, so I have no idea how many miles were on them. I gapped all of the old plugs and they were all over the 0.031" spec from the FSM by about 0.010" A couple of them were a lot looser than I was expecting and I found some oil and the spark plug wells, so I guess my valve cover gasket is starting to go as well.

I have changed the plugs and I will take a look at them again after a run through a couple of tanks of gas.

FWIW, the oil in the spark plug wells is likely the plug tube seals and not the valve cover gasket. All that will get sorted out when you pull the head...

 

[rosi6655]

If you still have the old plugs and know what order they were in, post pics of the tips and we can give you an armchair diagnosis.

I should have done that. I had them laid out by cylinder for a while, but I cleaned them up to see if I could see any damage. I will pull the new plugs after a few hundred miles to see how they look.

 

[rosi6655]

Got my Blackstone report in. No bueno. It looks like I have a head gasket job in my near future. The truck has also just started seeping oil externally on the exhaust side from what looks like the head gasket, but it is hard to tell.

 

[sbman]

Based on your leak down and compression test results I think you would be wanting to take care of the rings as well. I'd redo the leakdown and compression tests to see if that cylinder has improved or not, it's possible that it was just a stuck ring at the time of the test but if it's still that way it could be something more serious with that cylinder. Leak down tests are most valuable for comparison from test to test, the absolute values aren't as useful as seeing a change in the readings over time.

 

[rosi6655]

Based on your leak down and compression test results I think you would be wanting to take care of the rings as well. I'd redo the leakdown and compression tests to see if that cylinder has improved or not, it's possible that it was just a stuck ring at the time of the test but if it's still that way it could be something more serious with that cylinder. Leak down tests are most valuable for comparison from test to test, the absolute values aren't as useful as seeing a change in the readings over time.

I am planning to check things over again in a couple thousand miles. I replaced the spark plugs at the same time that I did the compression and leak down tests and the engine is running a lot better now with better fuel efficiency (~2mpg). I also plan to get a borescope to see if there is anything I can learn by looking at the piston and cylinder walls.

Best case scenario is this may be a sticky or gummed up piston ring. Are there any fuel or engine oil additives that would be worth using in the meantime that you all have had good results with?

 

[Malleus]

You can try Seafoam, but it's a crap shoot. It'll smoke a lot and you'll think you're burning carbon out of the engine, but in reality you're just burning the Seafoam. It works well as a soaking cleaner, but even then, it takes several days to really clean engine parts. IMHO, most, if not all, "additives" are snake oil.

If I had them in hand, I'd use CarbonOff instead. That stuff works in minutes. No good inside a running engine, though.

Once the head's off, and the shop has it, all the parts will be squeaky clean, so, other than the parts you keep, like the intakes, you really don't have any cleaning to do. I know that doesn't help now, but...

 

[vipergrhd]

I suggest do another comp. test hot and cold (wet), this will bring up the readings if your rings are worn.

 

[rosi6655]

You can try Seafoam, but it's a crap shoot. It'll smoke a lot and you'll think you're burning carbon out of the engine, but in reality you're just burning the Seafoam. It works well as a soaking cleaner, but even then, it takes several days to really clean engine parts. IMHO, most, if not all, "additives" are snake oil.

If I had them in hand, I'd use CarbonOff instead. That stuff works in minutes. No good inside a running engine, though.

Once the head's off, and the shop has it, all the parts will be squeaky clean, so, other than the parts you keep, like the intakes, you really don't have any cleaning to do. I know that doesn't help now, but...

I sort of get the same feeling about these additives. I have read the Safety Data Sheets on a few of them that include general information about their composition, and I don't see how they do anything that they claim to. For instance, Seafoam is a mixture of petroleum distillates, hydrocarbon-based solvent, and 10-30 isopropyl alcohol. When used in the recommended concentrations, I don't see where the magic happens.

I am hopeful that getting better combustion with the new spark plugs will somehow magically solve the uneven compression I saw in the last test. I will report back once I get a few more miles on the odometer and do another compression/leakdown test. As always, I appreciate you all taking the time to give me your feedback along the way.

 

[rosi6655]

I suggest do another comp. test hot and cold (wet), this will bring up the readings if your rings are worn.

I will do one around my next oil change and see if anything has changed.

 

[leonard_nemoy]

I have had a few very seasoned mechanics say to just add some diesel fuel to the oil and run it a bit before an oil change. Supposedly does the same thing as seafoam only better.