Low comp engine, trying thicker oil...

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Got the bad news today.....my 300,000 mile truck has two cylinders that are way under minimum spec compression. This is like hearing a family member has cancer. I've had this truck for 16 years. So before I start looking for a new engine, I thought maybe I'd try some thicker oils in a hail Mary attempt. The manual calls for 10w30. So should I go 10w40, or go for the gusto and buy some xw50?
 
Why not just do a ring job and head gasket if needed? Oil probably will not help with compression....is it burning any oil?

But to answer your question it will be helpful to know the make and engine. A 40 is what I would try first if shooting in the blind.
 
I don’t think thicker oil will help. As mentioned already, why not rebuild the existing engine? Make and model of vehicle will be helpful.
 
RESTORE!!!

61scTpw%25252Bj7L._SL1200___97465.1517348436.1280.1280.jpg
 
Originally Posted By: Linctex
RESTORE!!!

61scTpw%25252Bj7L._SL1200___97465.1517348436.1280.1280.jpg





He might need the 4 cylinder formula since we don’t know the engine make and size.
 
As suggested, the oil weight really doesn't have any affect on compression.

A compression certainly has a lot of value as an engine "snap shot" but I'd suggest doing a leak-down. This generally will allow you to pinoint where exactly you're losing compression and can show you how to proceed.

The whole engine is probably tired and could use a rehab after 300K miles, but you might get lucky and find a leaky exhaust valve or something like that. If that's the case, you can pull the head, lap or replace the valve(I'd probably just replace all of them as they're cheap) then slap it back together with a new head gasket.

Of course, how easy that is depends on what it is. Pulling a head on a small block Chevy or really most any OHV engine is a whole lot easier than on most any OHC engine.
 
Sorry, forgot to mention that it's a Ram 5.2 liter (318) magnum v8. OHV pushrod.
Ran like a champ until two weeks ago, then started idling rough and misfiring. Completely replaced all ignition components, still ran rough at low rpm. Did the comp test and found two bad cylinders. Number 5 and number 7 specifically.
 
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Originally Posted By: kawie_guy
Got the bad news today.....my 300,000 mile truck has two cylinders that are way under minimum spec compression. This is like hearing a family member has cancer. I've had this truck for 16 years. So before I start looking for a new engine, I thought maybe I'd try some thicker oils in a hail Mary attempt. The manual calls for 10w30. So should I go 10w40, or go for the gusto and buy some xw50?


Your rings are probably crudded up. You can try various things or do a ring job.
 
Originally Posted By: JLTD
Why not just do a ring job and head gasket if needed? Oil probably will not help with compression....is it burning any oil?

But to answer your question it will be helpful to know the make and engine. A 40 is what I would try first if shooting in the blind.


It's hard to say because it leaks a little. When I pull a trailer, it gets a little low on the dipstick quicker. But I never have to add more than a quart in 5000 miles. Always have used Valvoline Full Syn and oci of 3000 miles until last year when I went to 5000 based on uoa tbn. The truck's been babied.
 
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How about a leak down test? The fact this happened suddenly makes me wonder.

Or, just take the head off and see exactly what’s up.
 
Originally Posted By: PimTac
The fact this happened suddenly makes me wonder.



Yeah, me too. That's why I went through all the electrical stuff first. Thought something quick like that would be plugs, wires, sensors, cap and rotor, etc. The crankshaft position sensor did turn out to be bad, and replacing it did make it run better at speed, but it still runs rough at idle up to about 1800 rpm. I'm guessing thats because it's basically running on six uneven cylinders instead of 8.
 
Originally Posted By: Linctex
RESTORE!!!

61scTpw%25252Bj7L._SL1200___97465.1517348436.1280.1280.jpg



Does that stuff really work? I always thought it was snake oil.
 
Originally Posted By: Chris142
Often a sudden drop in compression between 2 cylinders is a head gasket is leaking compression between the cylinders.




This was something I thought about as well.
 
Originally Posted By: PimTac
Originally Posted By: Chris142
Often a sudden drop in compression between 2 cylinders is a head gasket is leaking compression between the cylinders.




This was something I thought about as well.


Which is all the more reason why you need to do a leakdown test before going any further.

BTW, what sort of absolute compression numbers are we talking for the "bad" cylinders and "good" ones?
 
Originally Posted By: bunnspecial
Originally Posted By: PimTac
Originally Posted By: Chris142
Often a sudden drop in compression between 2 cylinders is a head gasket is leaking compression between the cylinders.




This was something I thought about as well.


Which is all the more reason why you need to do a leakdown test before going any further.

BTW, what sort of absolute compression numbers are we talking for the "bad" cylinders and "good" ones?


I just went out and grabbed the test sheet. All the cylinders on the passenger side bank were at or slighty above 100. The two bad ones were 55 and 25. Then there was one at 75. So there was only one cylinder on the driver's side bank at 100.
 
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GOT SOME GOOD NEWS FOR YOU!!!
The "Restore" additive actually does work, and it works quite well. Helped me and thousands of other people to extend the life of engines, instead of doing costly rebuilds.



P.S. And I personally would use 5w40,10w40, or 15w40 from now on. Along with "Restore"
 
Originally Posted By: Chris142
Often a sudden drop in compression between 2 cylinders is a head gasket is leaking compression between the cylinders.


Bingo, two cylinders next to each other, happened rapidly, you lost a head gasket.

Replace the head gaskets. Rebuild the heads at the same time.

Or sell it and move on.

Or drop a new engine in it. 5.2 is pretty cheap in the junk yard.
 
Originally Posted By: Vladiator
GOT SOME GOOD NEWS FOR YOU!!!
The "Restore" additive actually does work, and it works quite well. Helped me and thousands of other people to extend the life of engines, instead of doing costly rebuilds.

P.S. And I personally would use 5w40, 10w40, or 15w40 from now on. Along with "Restore"


I agree 100%! Restore is a great product. Don't listen to all those who bash it and call it a "snake oil". People make blanket statements fail to separate it out from the junk products.

Restore + a slightly thicker oil is a perfect combo.
 
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