**please help** trouble with idle and voltage
Thread Starter
Seasoned Member
Joined: Oct 2011
Posts: 348
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From: Chicago
Year: 1989
Model: Cherokee
Engine: 4.0
Originally Posted by DFlintstone
I think the "HD" you see on the oil bottle means "high detergent". I remember an old chevy I had run on Pennzoil before high detergent was the norm. The valve cover was completely casted with gunk. Just clearance to let the rockers move.
Theory was you didn't want to switch to HD because when all that gunk came loose it would foul things up. (that is, switch without cleaning it up first).
If I was worried about some sort of contamination, I'd change the oil & filter, then just plan the next change sooner. If modern High Detergent oil can't get it to come loose and lodge in my filter, it can stay where it is as far as I'm concerned. Just my Two cents......
Theory was you didn't want to switch to HD because when all that gunk came loose it would foul things up. (that is, switch without cleaning it up first).
If I was worried about some sort of contamination, I'd change the oil & filter, then just plan the next change sooner. If modern High Detergent oil can't get it to come loose and lodge in my filter, it can stay where it is as far as I'm concerned. Just my Two cents......
CF Veteran
Joined: Aug 2011
Posts: 10,489
Likes: 24
From: Nor-Cal Coast
Year: 90,84
Model: Cherokee
Engine: 4.0,2.5
Cruiser is the man. /\. I was asking him about filters last week. I happen to like Castrol (so does my Beetle btw.)
http://minimopar.knizefamily.net/oil.../opinions.html
http://minimopar.knizefamily.net/oil.../opinions.html
CF Veteran
Joined: Aug 2011
Posts: 10,489
Likes: 24
From: Nor-Cal Coast
Year: 90,84
Model: Cherokee
Engine: 4.0,2.5
I might give that Rotella 15-40 a try. "MY" 30W Castrol only comes in $4.50 quarts, (Wall-mart). If it knocks, (again) on the multy grade, no loss, I'll have a years supply of oil for my chainsaw bar! (saw has been getting Castrol 10-40 this last year).
CF Veteran
Joined: Jun 2011
Posts: 2,858
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From: Nor-Cal
Year: 1990
Model: Cherokee
Engine: The venerable 4.0
Why would you use a 15-40... Cruiser have you read the very in depth explaination of viscosity at bobistheoilguy.com? It's called motor oil university I believe. I will never use anything thicker then a 5-30 again.
::CF Moderator::
Joined: Aug 2011
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From: Prescott, Az
Year: 1990
Model: Cherokee (XJ)
Engine: 4.0
Cuz in the factory owner's manual I have on my desk, and the one that was current in 1989, says that for temps down to 0* use 10w and for up to 100* use 40w. We always used the factory oil at the dealership that was a 15w40 since our temps varied from 0* to 100* throughout the year.
CF Veteran
Joined: Jun 2011
Posts: 2,858
Likes: 1
From: Nor-Cal
Year: 1990
Model: Cherokee
Engine: The venerable 4.0
It's just the fact that most automotive oils are the same viscosity at operating temperature. Even the heavy ones. The difference is more at cold start. There is no oil in automotive use today that is light enough to properly lubricate when cold but lighter oils become thin enough to lubricate much faster. Synthetics are even better because they are engineered to be a little lighter cold in comparison.
::CF Moderator::
Joined: Aug 2011
Posts: 43,971
Likes: 1,578
From: Prescott, Az
Year: 1990
Model: Cherokee (XJ)
Engine: 4.0
I would hope that the film left on my bearing surfaces from the previous shutdown would be sufficient to lubricate during the nano-second it takes for my Jeeps to build oil pressure. Ever disassembled an engine? No dry bearings in there. Can you imagine what the difference in viscosity is between 10 and 15 weight oils at 32*? Splitting hairs here.
Last edited by cruiser54; Dec 22, 2011 at 07:26 AM.