synthetic blend in an e39 m5

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hi everyone, long time lurker here first time poster!

i have an e39 m5 (1999 with the old version piston rings) which burns oil at a rate of 1L / 700km (435mi). i ran a compression test and the results are essentially minimum on one side obo 11.5 bar and the other bank is under 9bar down to even 8bar.

since new it has consumed castrol 10w60 (tws) and i recently switched to liqui moly gt1 10w60 in hopes of lowering the consumption a little bit to no avail.

to be clear i know the engine work that awaits and the $$$ involved but while i save up im trying to at least make the car usable in the mean time.

i noticed some people using motul 6100 15w50 and reporting much lower oil usage. im thinking of trying it for a bit before i essentially rebuild the engine but am a bit concerned since its a synthetic blend.

long story short, what do you guys think about risks of using this oil in the m5? doesnt seem too risky to me but i feel this is the perfect place to get informed opinions.

6100 spec sheet:

PROPERTIES
Viscosity grade SAE J 300 15W-50
Density at 20°C (68°F) ASTM D1298 0.876
Viscosity at 40°C (104°F) ASTM D445 143.4 mm²/s
Viscosity at 100°C (212°F) ASTM D445 19.6 mm²/s
Viscosity Index ASTM D2270 157
Pour point ASTM D97 -33°C / -27.4°F
Flash point ASTM D92 224°C / 435.2°F
TBN ASTM D2896 7.9 mg KOH/g

liqui moly gt1 10w60 specs:

Technical data
Viscosity at 40 °C 155 mm²/s
ASTM D 7042-04
Viscosity at 100 °C 23,8 mm²/s
ASTM D 7042-04
Viscosity at -25 °C DIN 51377
Viscosity index 185
DIN ISO 2909
Color number (ASTM) 3,5
DIN ISO 2049
Density at 15 °C 0,855 g/cm³
DIN 51757
Flash point 240 °C
DIN ISO 2592
Pour point -30 °C
DIN ISO 3016
Evaporation loss (Noack) 6,5 %
ASTM D 5800-08 Method
B
Total base number 8,0 mg KOH/g
DIN ISO 3771
Sulfate ash 1,2 g/100g
DIN 51575
SAE class (engine oils) 10W-60
SAE J300
 
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The worst-case scenario is that there will be some excess wear with the semi-synthetic. Unlikely, but possible. So, the real question is, what kind of rebuild were you planning for?

If you're planning on a comprehensive rebuild, then there's nothing to worry about. Even if there's excess wear on any given part, so what? You were going to fix it anyway!

On the other hand, if you're planning to be conservative with your rebuild, don't stray from the top-shelf synthetics. Your car specs them for a reason!
 
In the mean time, could you get away with using a mono-grade
SAE 40 or SAE 50?

If so, perhaps a very low ash CF-2 with a very high flash point
will help keep the spark plugs from fouling.
 
cool thanks for the replies guys!

my issue is im currently in serbia where the selection isnt as great and im going off of whats available.

i can get my hands on the full motul range, castrol, eneos, shell and others but i would not look at them.

what attracts me to the motul is the 15 weight which im hoping will be thick enough to "seal" it a little. also i like that the viscosity index is quite high and the oil looks promising.

regarding the rebuild thats a good point
smile.gif
for sure i will do the piston rings, rod bearings and probably the main bearings. the block will go to a shop to be looked at and repaired if need be. i may put in sleeves if needed and may replace the pistons as well but i cant say before its all inspected properly.
 
Originally Posted By: usce
what attracts me to the motul is the 15 weight which im hoping will be thick enough to "seal" it a little.

The W number isn't "weight." It's cold pumpability.


Originally Posted By: usce
also i like that the viscosity index is quite high and the oil looks promising.

Then it likely has a heavy dose of viscosity index improvers, which may or may not be a good thing.


Originally Posted By: usce
regarding the rebuild thats a good point
smile.gif
for sure i will do the piston rings, rod bearings and probably the main bearings. the block will go to a shop to be looked at and repaired if need be. i may put in sleeves if needed and may replace the pistons as well but i cant say before its all inspected properly.

What about the head?
 
@d00df00d

well there it is i came to the right place thanks for clearing it up, i should have said a heavier oil i suppose.

regarding the viscosity index improvers thats news to me thank you.

the head and block will both go for inspection to a machine shop, i apologize for generalizing.
 
True DoodFood,
I think he is going the wrong way,
"sold" on the concept of VI is the be-all
and end-all of engine oil selection.

Especially with an engine in the condition that it is,
and the weather is warm.
 
Originally Posted By: used_0il
True DoodFood,
I think he is going the wrong way,
"sold" on the concept of VI is the be-all
and end-all of engine oil selection.

Especially with an engine in the condition that it is,
and the weather is warm.


thanks for the input its much appreciated but im certainly not sold on it hence i came here to ask assuming a more knowledgeable group of people would shed more light on the subject which you have.
 
Happy to help.

I have a couple of friends with E39 M5s. They are serious machines. :]

Good luck. Hope all goes well for you!
 
It may be cheaper to find a used low mileage longblock out of a car that was wrecked FWIW. These engines are not inexpensive to rebuild.
 
Originally Posted By: OVERKILL
It may be cheaper to find a used low mileage longblock out of a car that was wrecked FWIW. These engines are not inexpensive to rebuild.


as i mentioned earlier im in serbia and the cost here will be low aside from parts obviously. i recently rebuilt the entire vanos system and checked the engine over as much as possible.

aside from the rings and oil consumption all looks healthy. the techs put a scope down the plenum and as much as could be seen looks good.

my fingers are crossed its just the rings and maybe some wear in the cylinders.

the price to disassemble, inspect at a shop and do minor work with reassembly is 1000eur here. ill be taking the car with me to north america so i want to take advantage of the cheap labour here while i can. i trust my mechanic and he rebuilds bmw engine on a regular basis, the vanos rebuild went extremely smooth for example.

been in touch with vac motorsports for the rings and bearings.
 
VAC is good, but BimmerWorks is better FYI.

Are you moving to the Philadelphia area?
 
Originally Posted By: d00df00d
VAC is good, but BimmerWorks is better FYI.

Are you moving to the Philadelphia area?


cool thanks ill send them an email regarding the parts i need. did not notice anyone other than vac offering parts directly online.

ill be going to florida as i cant stand the cold
smile.gif
 
You could certainy use this 15W-50 blend with no concerns as long as you keep drain intervals conservative, although with the consumption you're seeing that probably wouldn't matter anyway.
Unless you're tracking the car or otherwise running it really hard for extended periods, I doubt that the engine will suffer at all from the use of this oil.
If you're wise, you'll replace rod and main bearings when you have the engine apart, so it's not as though you have anything that needs to be saved from wear.
 
Originally Posted By: usce
Originally Posted By: OVERKILL
It may be cheaper to find a used low mileage longblock out of a car that was wrecked FWIW. These engines are not inexpensive to rebuild.


as i mentioned earlier im in serbia and the cost here will be low aside from parts obviously. i recently rebuilt the entire vanos system and checked the engine over as much as possible.

aside from the rings and oil consumption all looks healthy. the techs put a scope down the plenum and as much as could be seen looks good.

my fingers are crossed its just the rings and maybe some wear in the cylinders.

the price to disassemble, inspect at a shop and do minor work with reassembly is 1000eur here. ill be taking the car with me to north america so i want to take advantage of the cheap labour here while i can. i trust my mechanic and he rebuilds bmw engine on a regular basis, the vanos rebuild went extremely smooth for example.

been in touch with vac motorsports for the rings and bearings.


It's dealing with the block and the specific coating on the cylinder walls that is the potential expense. You'll probably have to get it bored and sleeved. That and of course the price of the parts.

Anyways, best of luck!
 
thanks to all for their informed opinions; i think i will go ahead and give it a try for the time being as the rebuild should be done in the next few months
smile.gif
 
Update: tried the motul 15w50 6100 synergie and the oil consumption is exactly the same (used a litre in about 700km/434miles). I think im noticing even more blue/black smoke than before. Hoping to do the rebuild asap and will go back to factory spec 10w60.
 
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