Leaking Oil Cooler

[Sven]

All,

I have sprung a leak.  1968 280SL, AT.  Yesterday, had a small patch of oil on the driveway (check every day).  Today, had a big patch of oil and a trail leading down the street into the driveway.  It is leaking motor oil near the base of the oil cooler (mounted on side of radiator, driver side). Luckily, I believe I caught it in time (car starts and idles fine).  Both bolts (hose connection, drain) at base of cooler are tight.  Are there o-rings or similar that could have blown? Or is the oil cooler blown?  Can the cooler be fixed similar to radiator?  Quick look on Miller's shows new one well over $400.  Have a 1970 280SEL parts car, but no oil cooler in it(?)

Any suggestions?  

Sven

[al_lieffring]

Sven

Back when I was working on these cars a common problem with the oil coolers was that the coolers are made out of aluminum and the line fittings are steel. dissimilar metals when in the presence of moisture causes galvanic corrosion, and an attempt to remove the lines from the cooler (especially the lower one) would usualy result in damage to the aluminum threads on the cooler. This was true on both the sedans and the roadsters. I don't recall if the sedan and roadster coolers are interchangable, but I don't think so.
First check the drain plug (Aluminum washer?), but because it is already leaking it sounds like the damage is already done so take off the lower cooler hose and check for damaged threads.

If someone has a "good news" answer to this one please post it.

quote:Originally posted by Sven

All,

I have sprung a leak.  1968 280SL, AT.  Yesterday, had a small patch of oil on the driveway (check every day).  Today, had a big patch of oil and a trail leading down the street into the driveway.  It is leaking motor oil near the base of the oil cooler (mounted on side of radiator, driver side). Luckily, I believe I caught it in time (car starts and idles fine).  Both bolts (hose connection, drain) at base of cooler are tight.  Are there o-rings or similar that could have blown? Or is the oil cooler blown?  Can the cooler be fixed similar to radiator?  Quick look on Miller's shows new one well over $400.  Have a 1970 280SEL parts car, but no oil cooler in it(?)

Any suggestions?  

Sven

113-042-10-014715
built 11 Jan 66
904/396 blue, Ivory Tex
condition- rust bucket

[ja17]

Hello Liefring and Al,

Yes, the aluminum oil coolers did have the fitting "siezure" problem, however they did not come along until about 1973. The early coolers were all steel and corrosion occurred at the lower cores where road salt was able to attack the steel. Repairs are not lasting if the problem is corrosion because other areas are weakened and may spring a leak at any time. Oil pressure on a cold engine may reach 100 psi (pegging the gage) more for an instant. These oil coolers are expensive and the W108 Mercedes six cylinder sedans used the same unit. In fact you will find that the first three digits of the Mercedes part number is  #108 .......... , indicating a "W108 sedan was the origin for the part.

It is unfortunate that your oil cooler from your parts sedan is missing because it is the same. Be careful that used units are free of corrosion. You can hook a coupling between the upper and lower oil cooler hose to bypass the oil cooler as a temporary repair. This is a much better alternative than running with a leaking oil cooler. Unless your running hard in a warm climate, the oil cooler is not that functional. Mercedes actually made a bypass fitting for this purpose, I do not have the part number at hand at the moment.

Back in the day, owners of 300SL Mercedes were instructed to block the oil coolers in their cars unless they were running hard. These early cars had oil temperature gauges and the 17 quarts of oil would never become hot enough to burn off contaminants in the oil under normal driving conditions! Blocking or by-passing the oil coolers help keep the engine oil temperature up.



Joe Alexander
Blacklick, Ohio

[Sven]

Joe and Al,

Thanks for the advice.  With the cooler months approaching, I am tempted to bypass the cooler and worry about it later.  Joe, you mentioned MB had a coupling for this purpose.  Can you simply fabricate a hose between the top of bottom cooler connections? or would it be easier and/or more appropriate to run the loop back near the oil filter?

Thanks in advance,
Sven

[ja17]

Hello Sven, Yes you can fabricate something, just be carefull it must hold a lot of pressure. The Mercedes part simply is a fitting which connects both ends of the rubber oil lines together, thus bypassing the cooler.

Joe Alexander
Blacklick, Ohio

[al_lieffring]

Dont the oil cooler lines run from the oil filter housing? Couldnt the filter mounting block be replaced with one from a 6 cylinder sedan without a cooler? a w111 or w114 220,230 or 250 would do it wouldnt it.

Al

113-042-10-014715
built 11 Jan 66
904/396 blue, Ivory Tex
condition- rust bucket

[ja17]

Hello Al,

Yes there were several configurations of housings. Some sedans did not have oil coolers. Some of the housings without coolers had the filter canister hanging staight down instead of angled. Actually the 230SL had the filter canister with the housing hanging staraight down. Most of these in that era were intechangable.

Joe Alexander
Blacklick, Ohio

[Sven]

Joe,
I tried talking with the local MB shop and they couldn't locate the part number for the oil cooler bypass coupling. Any chance it came to you in a dream last night?

All,
still would like to ultimately replace the leaking cooler rather than just bypass it all together.  Anyone know of or have a spare they would like to sell? Any recommendations where I can find a new one other than MB?

Thanks

[Sven]

All,

Does anyone know if oil coolers from any other MB model (other than 280 sedans) will work?  I have a friend with several oil coolers from later 1970's diesels.

Also, the part number for elusive oil cooler bypass coupling still avoids me.  I have called a lot of MB dealers and suppliers and can manage to find the part number or the part itself.  Any and all help will be much appreciated.

Regards

[George Davis]

Sven,

if you can't find the MB cooler bypass, you might try looking in the yellow pages under Hydraulic Equipment for someone who can make a bypass hose for you.

George Davis
'69 280 SL Euro manual

[Longtooth]

The 280SL's engine, M130, used a different oil cooler than the 2.5L engine M129.  The oil cooler wasn't introduced on the 6 cylinder engines until the 2.5L engine (M129) ... M129 was used first in the W108 sedan before the 250SL was introduced. M129 was a modified M127 2.3L engine and was developed in '63/'64. The decision to use the M129 engine in the W108 sedan was made in January '65. In the M129 engine the oil cooler mounts to the engine under the injector pump and below the motor mount.  I'm not familiar with the 280SL's oil cooler location.... but from what I've read on this site, it's not the same shape or mounted in the same location as on the M129.  The cuttaway view's I have of the M129 & M130 engine shows and label's the coil cooler clearly on the M129... but it isn't shown nor labled/listed on the cuttaway views of the M130... which leads me to believe it isn't mounted directly on the M130 engine.

The reason the oil cooler was introduced on the 2.5L M129 engine was because it ran hotter than the M127 (2.3L)... this because of the use of 7 main bearings instead of the 4 used on the 2.3L engine. The 1st 2.5L M129 engine was produced, and because of the incidence of siezed cylinder's in the 2.3L engines... and cooler oil tempertures helped reduce the incidence. The M130 used the same stroke as the M129, but a larger bore.  It also removed the water channels between the cylinder pairs that were on the M127 & M129 engines to accomadate the larger bore... as such, the M130 (2.8L) engine oil ran just as hot as the M129's... therefore the oil cooler was also required.

Bypassing the oil cooler in a 250SL and 280SL should be a temporary measure unless you never run the engine at high rpm for any significant duration, don't live in a hot environment, and don't get stuck in standing / stop/go  traffic very often.  It wouldn't be a bad idea to retrofit one in the M127 engine on a 230SL either if you're inclined to run at highway speeds (80+ mph) for long durations in hot environments.

Longtooth
67 250SL US #113-043-10-002163
'02 SL500 Sport

[ja17]

Hello Longtooth and Sven,

Yes the first  oil coolers were a optional bolt on offered on the 230SL. They reduced oil temperature by an engine oil heat to engine coolant transfer. They were standard equipment on the W108 250 series Mercedes sedans. The late W113 cars with the M130 engines (280 SL), had the oil cooler mounted next to the radiator, thus the rubber oil hoses running by the distributor and battery. These reduced heat by an oil temperature to  air temperature transfer. These oil coolers can be found on the later W108 Mercedes sedans (280 series).

Since some Mercedes sedans of the era with the M130 engines (W114 series) were equipped with NO oil coolers at all, I am more inclined to believe the oil cooler was added as a feature to offset heat in excessive conditions. These excessive conditions would be delivery of these cars to hotter climates, increase of factory AC, high performance driving, along with the higher operating temperatures.

Years ago I installed a oil temperature gauge on my M130 injected rally car engine. I was able to monitor the oil temperature in all conditions. Very hard competition driving caused the highest rise in oil temperature. Oil temperature was always slower to rise and slower to cool than the coolant temperature. Under severe competition it would acturally rise above coolant temperature. However you could always relate oil temperature to coolant temperature in general. In other words if your engine coolant is not overheated then your oil temperature will not be overheated. So your water temperature gauge will be an accurate barometer for you to use. You will not accidentally overheat your oil without you knowing it. Engine lubricants are also vastly improved over those used when these cars were new forty years ago.

Having your oil cooler functional is good insurance any way you look at it. If you are having over heating issues with your engine anyway the oil cooler is definately a plus. Otherwise I would not be afraid to operate the car under normal conditions without it.

I have been searching for the part number for the by-pass fitting. It is buried in my literature here somewhere.

Joe Alexander
Blacklick, Ohio

[Tom]

Joe,

Given how these cars tend to have coolant overheating issues, I wonder if the oil cooler could be modified to act as a supplemental water radiator?

Best,

Tom

1971 280sl Tunis Beige Metallic (restored & enhanced)
1971 280sl Tobacco Brown (low mileage stock)
1970 280sl Beach Driver with a touch of rust

[ja17]

Hello Tom,

Possibly, however having your engine oil at normal engine operating temperature as soon as possible is best so any contaminants will burn off.

Joe Alexander
Blacklick, Ohio

[Sven]

Thanks for all the great info. A new MB oil cooler is out of the question ($900+) and used ones are buyers beware. Adsit Company's website (a sponsor? and link provided on this site) shows a very reasonably priced oil cooler for our cars.  Does anyone have experience with this vendor?  I plan to call them tomorrow and discuss their cooler and see if there are any known issues with them, but would like to hear from someone with first hand knowledge of the company and their products rather than a salesman.

Thanks again Joe for taking your time to look for the bypass part number!

Sven

[Sven]

All,

I have recently aquired an oil cooler from a gracious member of our group.  The oil cooler is from a late 70's 280 (116) and not a 113 or 108.  The 116 cooler visually appears very similar to the 280sl cooler in size and dimension, with the exception of no drain plug and a different mounting configuration on the non-radiator side of the cooler (sl has a bolt connection near top of cooler, 116 does not).  The two lag bolt connections on the radiator side appear similar in location (hard to exactly tell, the 280sl cooler is still mounted).  I plan to pull the radiator and cooler out of the 280sl soon, but was wondering if anyone knows or has experience as to whether in fact the 116 cooler will work (i.e., mount properly)?  

Thanks,
sven