Dump Rotella T6 and use Delvac?
 

I religiously change oil every 6 months or 5,000 miles. In my W115 I go 6 months for 3,000 miles because of the age of and mileage of the car.

Anyway, I generally don't hit 3,000 miles in a 6 month time frame, so it comes down to time being the limiting factor.

I'm not sure what sort of oil the PO used, but I swapped it out for Rotella T6 5W 40. As time passed I started to develop leaks at the front and rear seals. Also, oil consumption increased. I understand there's a lot of urban myths about synthetic vs dyno. I don't want to go there. Besides, I'm not going to say that it was the oil's fault. The PO rarely drove the car whereas I'm averaging 5,000k/year. Those nagging issues were probably waiting for a serious driver to come along before their reared their ugly heads.

Anyway, I noticed that Delvac 15w40 is half the price of Rotella T6 today. Since I'm not going to see the full, long life benefits of synthetic, I'm thinking about switching to the Delvac.

Any thoughts or concerns?

Dave, do you experience winter where you operate the car(s)?

I have also had leaks with synthetic oil. The tale I was told is that the synthetic oil molecules do not form into the long chains typical of natural hydrocarbons and consequently can get out of small gaps in seals, etc., that block the non-synthetics. (This probably also gives them their cold-flow properties.)

Letting a car sit is probably the worst thing you can do (not your fault, obviously) for seals. They take a 'set' and won't seal properly, especially if they are as old as the seals in your '74 may be.

If you don't need synthetic for cold weather and you're not a high-mileage driver, you might as well go back to Delvac or whatever good traditional oil you prefer. I'll also be interested to hear what happens to your leak if you go off synthetic oil.

Jeremy

HMMM....I went to a synthetic 15-40 in the 240D at 321K, and we are now up to 347K. The engine wasn`t leaking before the switch, or is it leaking now. we got the car as it just turned 306K, and I have no prior maintenance before we got it.

My oil consumption hasn`t changed much from before we went to a synthetic.

Synthetic oil won`t cause a leak, if you have old seals and have been using regular oil, the synthetic will clean out the old gunk etc... that may have been plugging up cracks etc.... in the seals.

There are a ton of old wives tales floating around, just grab one you believe in.:D


Charlie

Answer
 

#1. Stop changing oil by calendar, unless you are in an extreme condensation area.
#2. Stop changing oil at 3000 miles.

3,000 mile myth - Wikipedia, the free encyclopedia
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Busting Oil Change Myth - YouTube
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HowStuffWorks "Do you have to change the oil every 3000 miles?"
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Stop Changing the Oil Every 3,000 Miles Already! | TIME.com
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Stop Changing Your Oil! - Edmunds.com
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http://www.nytimes.com/2010/09/11/your-money/11shortcuts.html?pagewanted=all&_r=0
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Changing car oil every 3,000 miles no longer needed

All modern oil is superior to 1970s - 1980's and earlier.

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Yes, we do. The car is garaged and it only goes out on warm, sunny days when. I don't drive it around town and avoid stop and go traffic/short drives.

I realize that syn offers better cold start up protection but it isn't that necessary for me.

I've done the switch in other, high mileage cars as well without issues. I actually use Mobile 1 in our other 3 cars.


I didn't want this to be another dyno vs synthetic debate which is why I mentioned old vs new driving habits as the primary suspected culprit.


So long as no one can provide evidence to the contrary I'll probably switch to Delvac for the cost savings alone. But if there is some improvement (doubtful), I'll be sure to post back.

Not to add fuel to the fire, but if I'm experiencing blow by wouldn't soot loading be a concern and cause the oil to become "contaminated", for lack of a better word, before it's time?

I know that I can extend the linterval for syn oil, but without testing the oil every few thousand miles the only indicator that I have to go on is the color of the oil. Color = nasty.

I believe Mobil 1 specifically says in its tech or marketing materials that it will not worsen any existing leak (they started saying that in the early 2000s, after a reformulation, it was not always their claim). As far as I know, no other synthetic says that.

I ran it in a really pooched, high-mileage Volvo 740 Turbo that both leaked and burned oil -- a model notorious for oil leaks and crankcase pressurization issues -- and I can confirm if anything it leaked LESS on Mobil 1.

I was under the impression that the "3,000 miles myth" applied only to gassers. I thought 3,000-4,000 was still preferable on diesels, due to soot concerns.

Answer
 

Color is useless, typically it changes in seconds or hours of running.
Your blow-by would need to be pretty spectacular to load the oil to a serious level in less than 5000 miles.

I test the oil when I get the vehicle (fresh oil change), at 6000 and 9000 miles, then decide what interval.

Thus far all of mine are 9000 mile oil changes, even though the test says it is not required for at least another 3000 miles, simply because I don't choose to push it further and feel better knowing it has reserve life if mechanical issues do occur.

For myself, it is cost effective at 9000 mile intervals to run synthetic oil.
Currently I re-test each engine once every 2-4 years depending on miles driven.

Blackstone Labs

Oil Analysis Kit - MyPilotStore.com

Engine Oil Analysis - Bob is the Oil Guy

HowStuffWorks "Engine Oil Analysis Kits"

Four Lethal Diesel Engine Oil Contaminants

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How often do you change the filter?

I have a Jeep engine that has leaked oil three seperate times on synthetic oil. Every time, I switched back to conventional oil at the next oil change and the leaks stopped. I am pretty convinced that synthetic oil will leak where conventional oil will not. If the "cause" of the leaks was "cleaned out old gunk," the conventional oil must have plugged the gaps pretty quickly.

What's the soot level at 9000 on a 617?

Do you go 9000 on the filter?

My own decision is 5000 based upon a 1% soot limit. Apparently you are OK with higher?

Answer
 

The critical factor for me is any engine coolant in the oil, that kills more engines than soot ever will.
By the time you see coolant (milkshake) discolored oil, it is usually a major engine and injection pump rebuild.


You are correct, I have run considerably higher, typically, the suggested limit for soot on the old mechanical injection diesel engines was 3-5%.

On my personal vehicles 2% soot with 0W-40 synthetic oil is simply indicating oil change needed now.

At 9000 miles my worst engine is 1.5%, the others vary between 0.5% and 1% soot load.

Please note that:
* I tune to the lean side for durability/MPG.
* Due to serious low diesel cetane issues I add 4-6 ounces of two stroke oil in every tank of fuel.
* Due to serious random fuel quality issues Biobor and StarTron are required frequently (more than 4 times per year).

The filters are changed every 3000 miles, they are cheap and easy.
If during engine service I suspect contamination, the oil is changed regardless of miles.
This is all a matter of choice to me.

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Looking at the numbers it's fairly easy to do a simple cost analysis for synthetic vs conventional oil. Rotella synthetic at $27.99 / gallon is about 55% higher than Delvac at $17.99. Increasing the drain interval by 55% to offset the cost means changing oil at 7750 miles instead of 5k, easily achieved by synthetics in most diesels. If we accept that most operating conditions for our engines do not require any other special advantages offered by synthetic oil then we've kept the lifetime cost of oil the same while achieving fewer oil changes.

But I often have a different take when asked about switching to synthetics. In this area we have high humidity, high winter salt usage, and some very rough roads. From this tech's perspective the cost of extended drain intervals on older vehicles in this market seems to be more surprise repairs involving more work and larger shop tickets. I counter the argument to spend more on synthetics by suggesting that using the oil change as a chance to check the car front to back means you're more likely to catch problems before they become major issues. If a DIY person feels there's a correlation between spending money and improving the perceived level of protection I'll recommend reducing drain intervals by 10%, staying with conventional oil, and dedicating an extra 1/2 hr with each oil change to inspecting other areas of the car. With poor quality replacement parts flooding the market I sometimes feel like I should be checking for problems weekly anyway.

Oil analysis is inexpensive and easy and can help you get much more than warm fuzzies from your maintenance program.