I had a leaky slave cylinder on my rear right wheel on my 1989 Chevy G20. Come to think of it, they don’t call them slave cylinder’s on the front. They call those calipers. It’s my first drum brake shoe change in years. They were soaked with brake fluid and it looked like I needed them out of the way to put in the cylinder.

It was a tough changing of shoes, if anyone was interested, it would take another thread.

The master cylinder is unusual on these rigs, there is a large reservoir for the front wheels and a small reservoir for the rear. Bleeding it was not going well so I took it to my mechanic who told me if you’re not careful you can mess up the master cylinder on that type.

I was about to embark on the trip and I realized my last oil change was 7500 miles ago. I use the economy Costco synthetic oil in hopes of prolonging the change interval - word is that you should change synthetic between 7500 and 10,000.

My mechanic who is pretty sharp says I should use Dino oil and change every 3000, that synthetic doesn’t work as well with older vehicles. 3000 miles comes around really quickly. I’m wondering if maybe I could stick with synthetic and change every 5000.

I have heard in the past that you really should use synthetic from the day it was born, that switching to synthetic mid life is not necessarily a plus.

Anybody know?

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1986 300SDL, 362K
1984 300D, 138K

There's no reason why you can't use synthetic. Except. Synthetic will loosen old deposits, which might cause problems. But you've already used it, so that's not a problem. And synthetic is better at finding leaky gaskets.


Nobody can just guess the best OCI for your car. What I would suggest is driving about 5000 on the synthetic, and sending a sample to Blackstone. They'll do a chemical analysis, and let you know whether you can push it further. Just include a note with your sample explaining what you are trying to do, and they'll return a personalized analysis:


https://www.blackstone-labs.com/


You have to order the "free" test kit before you change oil. The kit is free, the test isn't.

I use synthetic and test with this tester

https://www.amazon.com/Digital-Pressure-Testers-Detector-Analyzer/dp/B07MCWCSZ4/ref=mp_s_a_1_1_sspa?crid=162HIA7O4DU2C&keywords=engine+oil+quality+tester&qid=1686497579&sprefix=engine+oil+quality+%2Caps%2C197&sr=8-1-spons&psc=1&smid=A2KBISTF8R9JWQ&spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUEyUFU0MUlWWURCQVpOJmVuY3J5cHRlZElkPUEwNTU3NjEyM01EWktQS1M3WFU2UCZlbmN yeXB0ZWRBZElkPUEwOTg5NzcyMjIxSFdMTzVGM1NQWCZ3aWRnZXROYW1lPXNwX3Bob25lX3NlYXJjaF9hdGYmYWN0aW9uPWNsaWN rUmVkaXJlY3QmZG9Ob3RMb2dDbGljaz10cnVl

Two things concerning oil; one, change oil hot and change often. A bypass oil filter can filter down to 1/10th of a micron which helps to keep dirt and other particles filtered out of the oil; a good thing. Even with a bypass filter, I feel that oil should be changed at a minimum every 10,000 miles.

Also, there are several pre-charging systems on the market that are worth investigating. These pre-charging systems bring the engine oil pressure up to operating pressures before you start the engine. Having oil pressure prior to starting the engine lubricates the heads, valves, etc. This helps in a big way to alleviate engine wear.

As far as synthetic versus dyno, if your engine doesn't leak much, I believe synthetic is the way to go. There are several top notch synthetic oils on the market (check out bobistheoilguy forum for more information).

Great advice. I had a Blackstone kit, but never used it, not sure I could find it now.

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1986 300SDL, 362K
1984 300D, 138K

Interesting. I imagine a really deluxe way to go would be to do both: Blackstone and this device. And compare the results.

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1986 300SDL, 362K
1984 300D, 138K

I always change it hot. A couple of times I have gotten distracted and went close to 10,000 on synthetic. I’d prefer not to do that, but there was no obvious downside, of course that sort of damage can be small and incremental. A lot like starting your engine 1000 times with no oil pressure for the first X number of seconds. That’s an interesting device you speak of, I’m going to research that.

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1986 300SDL, 362K
1984 300D, 138K

Unless it makes your engine leak or burn too much oil fully synthetic oils are always the way to go because they pretty much halt the wear cycle wherever it is .

I've been using it for decades now and have several older, high mileage engines that run as-new on it, I deal with the weeps & seeps .

Oil is always the "Cheap Mechanic" .

__________________
-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

you got that right, an oil change is about the least expensive thing you can do for your car, truck or SUV that pays you major dividends in reduced maintenance costs. My father used to say oil changes are "cheap insurance".

I'd like to see the results. I can definitely see the oil moving up the scale on my tester over time but I've been really surprised with the Shell Rotella diesel synthetic I use that even approaching 7500 miles it never gets up to the very dirty end of the scale. It would be interesting to find an engine with 15k or so on the oil and put some on the tester. I can't bring myself to go 10k even when the tester says the oil is still good.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

Why using syn oil on older engines sometimes will not work....

If the engine has always used dino oil then the seals, like the crank seal, wear and the molecules of the dino oil are too large to pass by the wear.

Syn molecules are tiny and will find any tiny seal wear point to leak by.

Using sun from the start keeps these seals from wearing. It keeps everything from wearing.

So if you switch to syn on a high milage car and see leaks on the driveway then look for seals to change. Either that or go back to dino.

This doesn't mean you shouldn't use fully synthetic oils, it means you need to clean the engine now and then and address the weeps & seeps as you do routine maintenance .

__________________
-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better