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#4810743 - 07/10/18 09:23 PM Low comp engine, trying thicker oil...
kawie_guy Offline


Registered: 01/27/15
Posts: 80
Loc: utah,usa
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?

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#4810752 - 07/10/18 09:29 PM Re: Low comp engine, trying thicker oil... [Re: kawie_guy]
JLTD Offline


Registered: 12/15/17
Posts: 835
Loc: US
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.
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#4810759 - 07/10/18 09:35 PM Re: Low comp engine, trying thicker oil... [Re: kawie_guy]
PimTac Online   content


Registered: 03/04/17
Posts: 4611
Loc: Soviet State of Washington
I donít think thicker oil will help. As mentioned already, why not rebuild the existing engine? Make and model of vehicle will be helpful.
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#4810769 - 07/10/18 09:47 PM Re: Low comp engine, trying thicker oil... [Re: kawie_guy]
Linctex Offline


Registered: 12/31/16
Posts: 6186
Loc: Waco, TX
RESTORE!!!

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#4810785 - 07/10/18 10:07 PM Re: Low comp engine, trying thicker oil... [Re: Linctex]
PimTac Online   content


Registered: 03/04/17
Posts: 4611
Loc: Soviet State of Washington
Originally Posted By: Linctex
RESTORE!!!





He might need the 4 cylinder formula since we donít know the engine make and size.
_________________________
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#4810794 - 07/10/18 10:23 PM Re: Low comp engine, trying thicker oil... [Re: kawie_guy]
bunnspecial Offline


Registered: 11/23/15
Posts: 782
Loc: US
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.
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#4810801 - 07/10/18 10:28 PM Re: Low comp engine, trying thicker oil... [Re: PimTac]
kawie_guy Offline


Registered: 01/27/15
Posts: 80
Loc: utah,usa
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.


Edited by kawie_guy (07/10/18 10:34 PM)

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#4810802 - 07/10/18 10:28 PM Re: Low comp engine, trying thicker oil... [Re: kawie_guy]
Donald Offline


Registered: 03/21/04
Posts: 20550
Loc: Upstate NY
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.
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#4810810 - 07/10/18 10:37 PM Re: Low comp engine, trying thicker oil... [Re: JLTD]
kawie_guy Offline


Registered: 01/27/15
Posts: 80
Loc: utah,usa
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.


Edited by kawie_guy (07/10/18 10:45 PM)

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#4810815 - 07/10/18 10:41 PM Re: Low comp engine, trying thicker oil... [Re: kawie_guy]
PimTac Online   content


Registered: 03/04/17
Posts: 4611
Loc: Soviet State of Washington
How about a leak down test? The fact this happened suddenly makes me wonder.

Or, just take the head off and see exactly whatís up.
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Valvoline Advanced Synthetic 0w20
Mobil 1 M108A EP filter


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#4810822 - 07/10/18 10:51 PM Re: Low comp engine, trying thicker oil... [Re: PimTac]
kawie_guy Offline


Registered: 01/27/15
Posts: 80
Loc: utah,usa
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.

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#4810825 - 07/10/18 10:53 PM Re: Low comp engine, trying thicker oil... [Re: Linctex]
kawie_guy Offline


Registered: 01/27/15
Posts: 80
Loc: utah,usa
Originally Posted By: Linctex
RESTORE!!!



Does that stuff really work? I always thought it was snake oil.

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#4810827 - 07/10/18 10:59 PM Re: Low comp engine, trying thicker oil... [Re: Linctex]
aquariuscsm Offline


Registered: 12/30/06
Posts: 18287
Loc: Dallas,Tx USA
Originally Posted By: Linctex
RESTORE!!!



Restore AND 20W50!! laugh
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#4810828 - 07/10/18 11:01 PM Re: Low comp engine, trying thicker oil... [Re: kawie_guy]
Chris142 Offline


Registered: 06/05/03
Posts: 16957
Loc: Deplorable in apple valley, ca
Often a sudden drop in compression between 2 cylinders is a head gasket is leaking compression between the cylinders.
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#4810841 - 07/10/18 11:16 PM Re: Low comp engine, trying thicker oil... [Re: Chris142]
PimTac Online   content


Registered: 03/04/17
Posts: 4611
Loc: Soviet State of Washington
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.
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2017 Mazda CX-5 Grand Touring

Valvoline Advanced Synthetic 0w20
Mobil 1 M108A EP filter


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