Running with oil cooler bypassed - PeachParts Mercedes-Benz Forum

gozapper · #1 05-26-2015, 09:46 PM

Why do we need the oil cooler?

mach4 · #2 05-26-2015, 09:59 PM

Quote:

Originally Posted by gozapper

Why do we need the oil cooler?

To cool the oil.
To provide optimal oil volume for the engine.
To ensure the engine operates efficiently.
To prolong the life of the oil.

JB3 · #3 05-26-2015, 10:05 PM

The oil cooler flow is thermostatically controlled anyway usually, so oil is not always flowing.

mach4 · #4 05-26-2015, 10:48 PM

Quote:

Originally Posted by JB3

The oil cooler flow is thermostatically controlled anyway usually, so oil is not always flowing.

The manual states that the thermostat for the oil cooler starts to open at 95C (200F). I actually believe that it is flowing far earlier than that in practice. I have an oil temperature probe mounted on the feed line to the cooler and I typically see 150F at cruise. I don't think I've ever seen 200F on the oil, but on a long climb I can occasionally see 205F on my transmission cooler line.

To be fair, the real temps are probably a bit higher as I'm taking my reading off a clamp fitting on the line, not the actual fluid.

Here's the fitting I fabricated.

Maxbumpo · #5 05-27-2015, 08:32 AM

Engine oil is not only for lubrication, but also for cooling the engine. Mercedes typically over-designs every system, this is yet another example. The oil cooler is there to ensure the oil stays within a temperature range that it can properly lubricate and cool the engine even when you operate the car in extreme conditions.

Dan Stokes · #6 05-27-2015, 08:57 AM

I have bypassed it on my 617, but remember mine is race-only and does a mile at WOT and then cools off. Therefore, my use is not typical and I sure couldn't recommend it for daily use. Anyhow, mine does seem OK so far though I don't have an oil temp gage.

Dan

strelnik · #7 05-27-2015, 09:54 AM

Quote:

Originally Posted by Maxbumpo

Engine oil is not only for lubrication, but also for cooling the engine. Mercedes typically over-designs every system, this is yet another example. The oil cooler is there to ensure the oil stays within a temperature range that it can properly lubricate and cool the engine even when you operate the car in extreme conditions.

I am very happy that they over-design the engine.

This way, I don't have to buy a Dodge every 32,000 miles!

Walter K · #8 05-27-2015, 10:13 AM

I have a car with a turbo 617 that can run very hot in the summer, but the oil cooler has never been warm to the touch, unlike any other I have been around. I'm pretty sure at this point that the thermostat in the oil filter housing is stuck shut, and not allowing the oil to cool the engine. The thermostat is nla, but I recently got a cracked filter housing to take the thermostat out of.

I would not recommend running with out the oil cooler.

W.

JB3 · #9 05-27-2015, 10:18 AM

Quote:

Originally Posted by mach4

The manual states that the thermostat for the oil cooler starts to open at 95C (200F). I actually believe that it is flowing far earlier than that in practice. I have an oil temperature probe mounted on the feed line to the cooler and I typically see 150F at cruise. I don't think I've ever seen 200F on the oil, but on a long climb I can occasionally see 205F on my transmission cooler line.

To be fair, the real temps are probably a bit higher as I'm taking my reading off a clamp fitting on the line, not the actual fluid.

Here's the fitting I fabricated.

Very cool fitting!
I agree as well, i think it has some flow all the time.

Plus i havent read of anyone ever replacing that thermostat. I know i certainly have not on any of these cars. Makes me believe there is a certain percentage of cars with it stuck open or closed, and no reason to suspect thermostat due to how overbuilt the system is.

On my conversion i direct plumbed a cooler right in line before the feed to the oil filter with no thermostat. That worked well enough, though i was glad to move back to the stock housing later and adapt an aftermarket cooler to the stock housing.

SD Blue · #10 05-27-2015, 10:20 AM

All of the automotive diesel engines, that I've heard about, have an oil cooler. Since they use oil for piston cooling, it makes sense to have one. This is a diesel engine not gasoline and its cooling needs are different.

Another concept is thermal shock. Oil cooling also helps to maintain a more stable temperature, in parts of the engine, to help with longevity and reduce the chances of cracked heads, etc.

funola · #11 05-27-2015, 10:33 AM

Quote:

Originally Posted by Dan Stokes

I have bypassed it on my 617, but remember mine is race-only and does a mile at WOT and then cools off. Therefore, my use is not typical and I sure couldn't recommend it for daily use. Anyhow, mine does seem OK so far though I don't have an oil temp gage.

Dan

I do not follow the logic. How do you know it's OK if you do not have an oil cooler or an oil temp gauge?

Dan Stokes · #12 05-27-2015, 11:54 AM

The engine water temp stays on the low side all the time (usually about 160F) and the engine is always pretty cool to the touch after a run. If the oil were very much too hot the water temp would be higher and the engine would feel hot. I have a temp gun and intend to shoot the oil pan after a run at the next meet.

Again, I stress that my use is atypical and should not be taken as a guideline for a street engine.

Dan

mach4 · #13 05-27-2015, 07:17 PM

On the way back from a nice drive around town I took a screen capture of my gauges app on my Android to illustrate my contention that the cooler actually works at temps lower than 200. Note specifically that the oil temperature was 151 degrees. I felt the oil cooler just to confirm that the cooler was active and the temp wasn't due to just radiated heat from the eigine, and while it was clearly not 200 degrees it was hot - 150-ish hot. The other temps that might need some explanation to complete the picture are Arduino temp - this is a proxy for engine bay temperature as the temp sensor is actually on the Arduino microprocessor board mounted in a plastic case in the engine bay, drivers side toward the front; Intake temp - this is taken from the air cleaner housing, passenger side front; TIT - this is "turbine inlet temperature" commonly called EGT (exhaust gas temperature) if taken in the exhaust pipe. Mine is situated in the pipe leading from the exhaust manifold to the exhaust turbine wheel. (From boost and TIT readings it's evident I was climbing at the time). Ambient temp was around 80 at the time. Fuel pressure, Voltage and Vacuum are pretty normal.

vstech · #14 05-27-2015, 08:24 PM

I think of it this way... The turbocharger has oil constantly flowing through it... The exhaust side of the turbo sits around 900F sometimes... The Pistons during combustion stroke exceed 400F... The surface likely hits 1500F... That's a lot of heat to dissipate into the oil... The heads have oil flowing in them building up heat into the oil... The cylinders are cooled by the water jacket, but the oil is cooled by what?

I wouldn't be surprised if the cooler partially opened below 200... But it would be hard to tell... Since the flow would be sporadic, and it would mix with bay temp oil already in the lines...

mach4 · #15 05-27-2015, 08:52 PM

Quote:

Originally Posted by vstech

The cylinders are cooled by the water jacket, but the oil is cooled by what?

Another thing to consider in this discussion is that in the later engines the upper oil pan was no longer smooth, but rather had some "waffling" cast into the rear portion of the pan. I don't think it's there for structural reasons but rather to provide yet more cooling to the oil in the pan by providing more surface are for heat radiation. I'm running the smooth pan for clearance reasons, so more than happy to have an efficient and effective oil cooler.