Synthetic oil: Diesel mechanic says no - Page 3 - PeachParts Mercedes-Benz Forum

Stretch · #31 08-04-2011, 03:24 PM

Quote:

Originally Posted by scottmcphee

To Borat's amazement, the whole isle of cheese, http://www.youtube.com/watch?v=Kz8OkD6llGY

Great stuff - I just need to get the suit - I've already got the SYNTHETIC oily hair!

scottmcphee · #32 08-04-2011, 03:24 PM

I knew a "diesel mechanic" who thought it was perfectly fine to run green coolant in the 87 300D he was trying to sell me. I asked to see what coolant and he showed me a Prestone jug. I told him "wrong stuff"... and he reacted like I was insulting his mother. Didn't buy the car, even though it had a recent #22 head job put on it. Should have.. in hind sight.

So, I don't automatically give much credit when hearing the credentials "diesel mechanic". I figure he knows how to work on a Caterpillar. I don't. Good for him.

cjlipps · #33 08-04-2011, 04:00 PM

I'll just throw in here. I've run synthetic in every vehicle I've owned since 1987 (and that hasn't been a small number). I've installed it in vehicles with mileage ranging from 180K to brand new (1K) and everything in between and have never caused or exacerbated a leak. In addition, without exception, the vehicles that consumed oil when I got them experienced reduced oil consumption after using the synthetic.
One interesting story was with a 1990 300E that used a qt every 1400 mi when purchased (with 116K). After changing to synthetic the consumption went to 1200, 1000 and 800 miles per quart used then jumped dramatically to a qt every 4000 miles where it remained until I sold it with 165K.
In short, I'm a fan of synthetics and I maintain that a healthy engine can only benefit from its use. Any 30 year mechanic should recognize that automotive technology has advanced immensely during his career and realize that lubrication technology has to keep pace.

sixto · #34 08-04-2011, 08:04 PM

You mean consumption dropped.

Sixto
87 300D

tangofox007 · #35 08-04-2011, 08:29 PM

Quote:

Originally Posted by sixto

You mean consumption dropped.

Sixto
87 300D

Or jumped down!!!

Orv · #36 08-04-2011, 08:30 PM

Quote:

Originally Posted by scottmcphee

I knew a "diesel mechanic" who thought it was perfectly fine to run green coolant in the 87 300D he was trying to sell me. I asked to see what coolant and he showed me a Prestone jug. I told him "wrong stuff"... and he reacted like I was insulting his mother. Didn't buy the car, even though it had a recent #22 head job put on it. Should have.. in hind sight.

I tend to think that, in practice, what coolant is used matters less than how frequently it's changed. Most people don't change either type often enough, so the corrosion prevention additives wear out. I'm as guilty as anyone; it's a messy job and nearly impossible to do thoroughly if you don't have access to a garden hose.

EDBSO · #37 08-04-2011, 09:16 PM

Quote:

Originally Posted by Orv

I'm as guilty as anyone; it's a messy job and nearly impossible to do thoroughly if you don't have access to a garden hose.

I had a conversation with a fleet maintenance manager and he popped off the lower rad hose every couple of years and topped up with fresh coolant of choice. He felt that this way it was fast and replenished the additive packages. He has been doing it that way for decades without problems.

cjlipps · #38 08-05-2011, 01:29 AM

Quote:

Originally Posted by tangofox007

Or jumped down!!!

The numbers make more sense than my statement did. Guess I had to mean jumped down.

Anyway it was better for me.

otto huber · #39 08-05-2011, 09:27 PM

Before I switched to synthetic last month, I would have to feather the accelerator for about 5 seconds upon first start in the morning in order to maintain idle. I figured that it was a fuel delivery issue and was surprised to see the problem go away after switching to synthetic.
My turbo drain tubes are leaking less, and the leak from the intake manifold seems to be smaller now. The oil filter housing gasket repair I did 6 months ago is holding up fine. No new leaks on an engine with 181K.

Stevo · #40 08-06-2011, 11:22 AM

I have found that small oil leaks went away when I switched to Amsoil 15/40 about ten years ago. I would have second thoughts about any mechanic who bad mouths synthetic oil.

FinnJohn · #41 08-06-2011, 11:25 AM

Twelve thousand miles?! Yeouch! My understanding is that it's soot load rather than actual molecular breakdown that causes diesels to need more frequent oil changes -- which is why I've never bothered with synths, because no matter what kind of crank sauce is in there, it's not gonna get any more or less sooty over 3,500 miles. I would think at 12,000 your oil would have turned into lapping compound ...

... am I wrong about this? Oil changes in a 115 are an upside-down finger-burning oil-in-your-face *****, and I would LOVE to do them less frequently!

--Finn

Quote:

Originally Posted by curtludwig

So we should all go back to mineral based 30wt and change at 3,000 miles? No thanks.

"Synthetic" is such a crap term, cheap "synthetic" oils (meaning any synthetic that costs less than $5/qt) is actually highly refined conventional oil. "Real" synthetic like Mobil 1 or Amsoil or Royal Purple is a whole different thing.

Will the car leak more with synthetic? Maybe.
Will it start easier in the cold? Yup.
Can you go longer between oil changes? On a 60x engine yes, on a 61x not without additional filtering.
Will synthetic oils clean my engine internals? Probably.
My '85 190D had high iron levels when I first started using Mobil 1 5w40 (and analysis obviously) but after each oil change the iron levels would rise more slowly and finally (after 20,000 or so miles) they stayed within normal levels. In that car I changed the oil on 12,000 mile intervals.

Loads of people say "Change the oil at 3,000 miles, its cheap insurance!" Sure, whatever, thats probably fine. If I did that I'd have to change the oil every other month. No fun at all, I've got better stuff to do. Remember to figure in your time during an oil change, based on what I make thats a third of the price of the whole oil change...

Think of the leaks as synthetic oil showing you where the leaks are so you can fix them

sixto · #42 08-06-2011, 02:12 PM

No thinking person stretches 12,000 miles on a dare. I'm sure there's oil analysis to back up the extended interval.

Sixto
87 300D

Orv · #43 08-06-2011, 06:02 PM

I think the problem isn't so much that the soot can act as an abrasive -- the particles are smaller than the bearing clearances, which is why it goes through the filter. The problem is if the oil gets too loaded with it it gets thicker, and eventually the soot might start to settle out as sludge.

I recall someone who had a diesel Rabbit and was using synthetic and doing oil analysis. The break point for changing the oil ended up being when the soot suspended in the oil started to make it more like 50-weight than 40-weight, viscosity-wise. Kinda like corn starch in gravy.

wildest · #44 08-06-2011, 06:47 PM

My first experience with the oil wars was regarding my bike about 22 years ago, and the consensus then was a resounding "no" from a couple of mechs whom I respected for the most part, but were wrong about this regarding air-cooled bikes., at least for me and my anecdotal results.

Then I ran into it on a Volvo forum/elist that someone on summed up by stating that the odometer would run backward if you used synthetic oil in your gas redblock (after a particularly long exchange), with a well regarded Volvo diesel guy running on 25000 mile change intervals with oil analysis backing him.

All I can chime in with as far as real world observation is that my International/Ford 7.3 liter diesel has 351,000 miles on it and makes almost no smoke, except for black on hard acceleration, and uses no oil except for the 1/2 quart drop the 1st 500 miles after a change, at approximately 5k mile intervals, and has done that since new. On synthetic since the 3rd oil change. My bike has done it's mileage with the cases never having been split (no bottom end work yet) and all the gasser Volvo's went at least 300k, except for the '95, which electrical problems are killing. And the '90, which only has ~147k on it so far.

So with the '79 and '85 300D's we now have, I will run them on synthetic and feel good about it. Probably 5k intervals, and maybe even an oil analysis, but maybe not.

vstech · #45 08-06-2011, 07:36 PM

bottom line...
synthetic is a more stable oil stock. it may clean gunk and allow bad seals to leak, it may not.
more efficient motors can handle long oil change intervals with it, but the 617 and older motors have such a high soot load, it's not recommended due to soot load.
I use synthetic oils in everything I own, and have long OCI on the motors that can handle it. however, on those motors, I change the filter 3/4 of the way through the duration.