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Low comp engine, trying thicker oil... #4810743
07/10/18 09:23 PM
07/10/18 09:23 PM
Joined: Jan 2015
Posts: 174
utah,usa
kawie_guy Offline OP
kawie_guy  Offline OP

Joined: Jan 2015
Posts: 174
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?

Re: Low comp engine, trying thicker oil... [Re: kawie_guy] #4810752
07/10/18 09:29 PM
07/10/18 09:29 PM
Joined: Dec 2017
Posts: 1,746
US
JLTD Offline
JLTD  Offline

Joined: Dec 2017
Posts: 1,746
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.


I use the overseas owner's manual to choose my oil.

Using AMSOIL™

Hers: 2008 Jeep Liberty 143k, SS 5w30/Amsoil

His: 2015 4Runner 51k, OE 5w30/Wix

Re: Low comp engine, trying thicker oil... [Re: kawie_guy] #4810759
07/10/18 09:35 PM
07/10/18 09:35 PM
Joined: Mar 2017
Posts: 8,252
...
PimTac Offline
PimTac  Offline

Joined: Mar 2017
Posts: 8,252
...
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.


Cannot see signatures any longer so it doesn’t matter.
Re: Low comp engine, trying thicker oil... [Re: kawie_guy] #4810769
07/10/18 09:47 PM
07/10/18 09:47 PM
Joined: Dec 2016
Posts: 8,017
Waco, TX
Linctex Offline
Linctex  Offline

Joined: Dec 2016
Posts: 8,017
Waco, TX
RESTORE!!!



"The evidence demands a verdict".
(Re:VOA)"it's nearly impossible to actually know the particular additives that are in there at what concentrations."
Re: Low comp engine, trying thicker oil... [Re: Linctex] #4810785
07/10/18 10:07 PM
07/10/18 10:07 PM
Joined: Mar 2017
Posts: 8,252
...
PimTac Offline
PimTac  Offline

Joined: Mar 2017
Posts: 8,252
...
Originally Posted By: Linctex
RESTORE!!!





He might need the 4 cylinder formula since we don’t know the engine make and size.


Cannot see signatures any longer so it doesn’t matter.
Re: Low comp engine, trying thicker oil... [Re: kawie_guy] #4810794
07/10/18 10:23 PM
07/10/18 10:23 PM
Joined: Nov 2015
Posts: 879
US
bunnspecial Online content
bunnspecial  Online Content

Joined: Nov 2015
Posts: 879
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.


2010 Lincoln MKZ-Mobil 1 5W-30
1970 MG MGB Roadster-Valvoline VR-1 20W-50
Re: Low comp engine, trying thicker oil... [Re: PimTac] #4810801
07/10/18 10:28 PM
07/10/18 10:28 PM
Joined: Jan 2015
Posts: 174
utah,usa
kawie_guy Offline OP
kawie_guy  Offline OP

Joined: Jan 2015
Posts: 174
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.

Last edited by kawie_guy; 07/10/18 10:34 PM.
Re: Low comp engine, trying thicker oil... [Re: kawie_guy] #4810802
07/10/18 10:28 PM
07/10/18 10:28 PM
Joined: Mar 2004
Posts: 21,857
Upstate NY
Donald Offline
Donald  Offline

Joined: Mar 2004
Posts: 21,857
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.


2015 Subaru Forester 2.5 engine/CVT
2015 Ford F250 w/Powerstroke
2016 Subaru Crosstrek CVT (wife's)
Re: Low comp engine, trying thicker oil... [Re: JLTD] #4810810
07/10/18 10:37 PM
07/10/18 10:37 PM
Joined: Jan 2015
Posts: 174
utah,usa
kawie_guy Offline OP
kawie_guy  Offline OP

Joined: Jan 2015
Posts: 174
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.

Last edited by kawie_guy; 07/10/18 10:45 PM.
Re: Low comp engine, trying thicker oil... [Re: kawie_guy] #4810815
07/10/18 10:41 PM
07/10/18 10:41 PM
Joined: Mar 2017
Posts: 8,252
...
PimTac Offline
PimTac  Offline

Joined: Mar 2017
Posts: 8,252
...
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.


Cannot see signatures any longer so it doesn’t matter.
Re: Low comp engine, trying thicker oil... [Re: PimTac] #4810822
07/10/18 10:51 PM
07/10/18 10:51 PM
Joined: Jan 2015
Posts: 174
utah,usa
kawie_guy Offline OP
kawie_guy  Offline OP

Joined: Jan 2015
Posts: 174
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.

Re: Low comp engine, trying thicker oil... [Re: Linctex] #4810825
07/10/18 10:53 PM
07/10/18 10:53 PM
Joined: Jan 2015
Posts: 174
utah,usa
kawie_guy Offline OP
kawie_guy  Offline OP

Joined: Jan 2015
Posts: 174
utah,usa
Originally Posted By: Linctex
RESTORE!!!



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

Re: Low comp engine, trying thicker oil... [Re: Linctex] #4810827
07/10/18 10:59 PM
07/10/18 10:59 PM
Joined: Dec 2006
Posts: 19,453
Dallas,Tx USA
aquariuscsm Offline
aquariuscsm  Offline

Joined: Dec 2006
Posts: 19,453
Dallas,Tx USA
Originally Posted By: Linctex
RESTORE!!!



Restore AND 20W50!! laugh


1996 Nissan 300ZX 5-speed,Arctic Pearl(#175 of 300)
Quaker State Ultimate Durability 10W30
2012 Honda Accord Coupe EX-L 2.4,auto,San Marino Red
Pennzoil Platinum HM 10W30

Re: Low comp engine, trying thicker oil... [Re: kawie_guy] #4810828
07/10/18 11:01 PM
07/10/18 11:01 PM
Joined: Jun 2003
Posts: 18,428
Deplorable in apple valley, ca
Chris142 Offline
Chris142  Offline

Joined: Jun 2003
Posts: 18,428
Deplorable in apple valley, ca
Often a sudden drop in compression between 2 cylinders is a head gasket is leaking compression between the cylinders.


02 Wrangler carlube 5w30
87 F250 traveler 15w40
07 fjcruiser Chevron 10w30
Z400 castrol T 10w40
Can am maveric edge 5w40
57 case tractor 15w40
Re: Low comp engine, trying thicker oil... [Re: Chris142] #4810841
07/10/18 11:16 PM
07/10/18 11:16 PM
Joined: Mar 2017
Posts: 8,252
...
PimTac Offline
PimTac  Offline

Joined: Mar 2017
Posts: 8,252
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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.


Cannot see signatures any longer so it doesn’t matter.
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