Lubricants???

I want to switch to synthetic engine oil on my next oil change. Is there anything that I should be aware of in a switch over? What oil weight should I use in a synthetic?

Also, what type of lubricant goes in the Model 30 front axle? Same for the 35 in the rear?

1990 MJ Pioneer, 4wd, 127k

Thanks PRL

I switched to 10-30 Mobil One and use a K&N oil filter.
This is heresay in regards to the synthetic fluid but...on older engines leaks may develop where there weren't leaks previously. I will also add that my engine oil stays cleaner longer since I quit using a K&N air filter element.

On the axle lube I used Valvoline 75-90 synthetic both front and rear. It has two years/40K miles on it now and I am planning to change before the summer.

Good luck,
Tom

we should clarify that the leaks aren't caused by the synthetic lube, but by their ability to clean the sludge that was previously masking them.

fwiw, i switched to mobile 1 synthetic @ 95,000 and have developed no leaks since (5,500 miles later).

I changed over to mobil 1 10W-30 at 130,000 miles. I had replaced the valve cover gasket, oil filter adaptor, and oil pan gasket before I switched. Those gaskets were replace as maintenance, no on a whim.

I still had the factory timing chain cover gasket, rear main seal, crankshaft damper gasket and so far no leaks 20,000 miles later.

The worst case is if the synthetic cleans all the crud of the rear main then you will have to have a new seal installed. That not cheap so you may want to dump $500 in oil to top it off vs fixing the leak. The rear main leak is the only risk you are taking.

I'd change to synthetic and see what happens.

Thanks all...

In regards to the front axle...I am going to be working on my vacuum disco this week and I have heard that even with it jacked up on the right some lubricant may leak out. Can I top off the axle with a sythetic or should I just use the regular lube since I do not plan on a complete drain of the system?

I would use more of the same when you top off your axle. I found in the 88 XJ/MJ shop manual that the shift motor pocket is to have 5 oz of lube in addition to the lube in the pumpkin. I did not cross my mind the shift motor pocket needed lube until I read it.

I just finished a reman install last weekend and plan to switch to Mobile 1 at the 500 mile mark (initial engine break-in). I've read recommendations in a couple of other threads that oil pressure may drop a bit when switching to synthetics and it might be better to bump up to a 10W-40. Any experience or thoughts on this?

desertred said:

I just finished a reman install last weekend and plan to switch to Mobile 1 at the 500 mile mark (initial engine break-in). I've read recommendations in a couple of other threads that oil pressure may drop a bit when switching to synthetics and it might be better to bump up to a 10W-40. Any experience or thoughts on this?

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I switched my '88 to synthetic at around 175,000 because the highway oil pressure had dropped to below 40 psi. I initally ran Mobil-1 10W30 and that got me back up to about 40 psi. Then I discovered that Castrol has a 5W50 synthetic so I now run that year 'round and my highway pressure even on a long trip stays between 45 and 50 psi.

Synthetic in the same weight as conventional should produce better oil pressure, not worse.

After two full synthetic oil changes I noticed that I could hear the classic piston slap noise. Perhaps the oil was too slick???
I drained a little and added in a quart of 20-50 and the piston slap noise stopped.