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Discussion Starter · #1 ·
I swapped to synthetic Castrol oil in my 91 Jeep wrangler.(4.0L). It had about 75000 miles at the time. I now have a real problem and it appears that I will have to rebuild the engine. Seemes changing the oil to synthetic on a high milage engine can be a fatal mistake.....Anybody know any hi-performance engine builders who can help me?

 
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Discussion Starter · #2 ·
Curious....what problems did you have?

LarryM
85 CJ7, 350TBI ,T19 4spd
'00 TJ Sport, NV3550 5spd, D44, Teraflex system
 

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Keep in mind, that using to synthetic oil too soon is a bad thing as well, because it doesn't allow everything to wear in properly. I've heard some recommendations before that you shouldn't use synthetic before the engine has between 7500 and 10000 miles or so on it with conventional oil first.

Tim
"The_Sandman_454"

/wwwthreads_images/icons/cool.gif '79 Suburban 4x4 454, 6" lift, 35x12.5s & '85 GMC S15 4x4
 

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Yes..........I'm curious as well. Besides being more thermally stable ............what's the difference? It just gives you what oil ideally gives you at normal operating temperatures ........when it's not normal operating temperature ...either hotter or colder. While a "normal" breakin period is advised .............I've never heard any problems with synthetic that you wouldn't have with any other conventional oil. That is, if you consume a lot of conventional oil ......you'll probably consume a fair amount of synthetic oil. Now ......in performance motors ........Mobil makes the 15-50 weight synthetic which is recommended for turbos and other "extreme" motors.......I'll never use anything but a synthetic oil in a gas motor.......especially one that I own from new.

What happened to this motor?

GeeAea

 
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Discussion Starter · #5 ·
I doubt that switching to the syntetic oil actually caused your engine to be damaged. Synthetics are simply molecules of oil that have been made in a "lab" vs. being made by nature. Less irregularity, fewer imperfections, less inherent contamination. This can cause an engine to experience a higher rate of oil consumption and/or oil loss. I'm just guessing, but are you experiencing blow-by at the piston rings and now need a rering? This is a common problem and would have occured with or without the synthetic oil. Since synthetics can "leak" past piston rings easier the problem appears to be worse because more oil is carried past the same piston rings by the blow-by than there would be with a standard oil. This is the case with all oil consumption/loss problems and synthetic oil.

"My other car is a BULLDOZER"
 
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Discussion Starter · #6 ·
The thing about switching to syntetic on a high milage engine is that the synthetics are so good at cleaning that they actually clean out the gunk that has been holding your engine together. They can break down sludge that is acting as a gasket, and can also clean up the cylinder walls so well that you actually start to experience blowby that was not occuring before due to the carbon buildup, and whatever else may be there.

In other words, yes, the oil could have contributed to the engine failure. Not because it is not a quality oil, but rather ironically enough, because it is TOO good of an oil. Some of the recently liberated sludge could have blocked an oil poassage to a bearing or bearings, or any number of other things. Many "experts" recomment that if you relly want to go to a synthetic (not in and of itself a bad idea), you should first clean the engine with a light oil, running it at idle to about 2000RPM for about 20 minutes with the "flushing oil" in, then drain it, change the filter, and fill 'er up with the synthetic.

I believe that http://www.geocities.com/MotorCity/2195/engineoil_bible.html explains a lot about this process very well (as welll as a lot of other cool oil-related info), and http://www.ucs.mun.ca/~t56blt/xj750/tech/oilfaq.txt has some good hard numbers on different brands and weights of oil. This second site really has no bearing on the discussion here, but it is kinda cool to see how your brand compares to the others.

Hope this helps!

Marc
Contagious Racing
ICQ: 20889115
 
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