1982 R100RT Oil Cooler Delete?

Hello to the community,

Relatively new member here. I have embarked down the dark path of rescuing an '82 R100RT. The original body work was in relatively rough shape, so as I rebuild the bike I am going to do so without the OEM fairings. Naturally I am attempting to streamline things as much possible, and would like to delete the oil cooler assembly.

I've gone as far as sourcing all the related items from the EV, most importantly these items that differ from the oil cooler version specs.

Oil Filter Cover: 11421263345
Pipe(short): 11111263342

What I am seeking via this post is whether or not this is a terrible idea, or detrimental to the engine. I have seen some content out there that makes this seem like a no brainer. But I've also seen some threads that caution doing this.

Would anyone possibly be willing to share any related experience or intel here? A great many thanks in advance. -G

Oil cooler

I had an oil cooler on my RS and got rid of it. Unless you are riding in extremely hot conditions, you don't need one. Talk at my local airhead shop also took the view the RT mounted cooler in front of the engine when it was working added extra heat to the diode board under the front cover. That the shop talk, no real proof. Don't idle for long periods of time and keep oil of proper viscosity and changed regularly.

As for me, I don't need and never had needed a cooler, the bike came with one and it was a big pain in the butt to change the fitler with the cooler on. If I rode in the desert or some extremely hot climate, I might change my mind. I have a friend in AU where it gets to 105F in the summer and his R90S has no cooler.

You have the list for parts you need as well as a non oil cooler filter and you are good to go. Be sure to get the proper oil filter for a non cooler bike. St.

STEVENRANKIN said:

I had an oil cooler on my RS and got rid of it...

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Hello Steven, many thanks for your sharing on this. I am going to follow your lead on this. Many thanks. I think I was most concerned about making sure that I had all the correct parts, and as you mention the correct filter for the non-filter spec.

I'll be sure to triple check things... Thanks again.

If you do decide to delete it, I'd suggest holding onto the parts for a bit. The BMW oil cooler is a nice piece that does its job well; if you put it on the marketplace, someone will likely want it if you determine you don't want or need it.

I added one to my R80/7 many years ago after corresponding back and forth with Oak. It definitely works well to keep oil temp within spec when riding in hot conditions, at high speed, in the hills/mountains, and/or 2-up with a load. I always found the most troublesome part of oil filter maintenance is the fairing. Changing the filter on my RS with the fairing and oil cooler thermostat is more troublesome that the same setup on my /7 without the fairing.

jad01 said:

If you do decide to delete it, I'd suggest holding onto the parts for a bit...

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Thank you jad01, appreciate that advice. I will definitely be hanging on to it, just in case things need to be swapped back.

paper gasket?

Now, with the stub pipe installed, a canister depth of ~3.1mm, and the correct filter, white o-ring etc... I am wondering if I should install using a fresh paper gasket?

Snowbum's (excellent) site states you likely don't need it. Largiader's (also excellent) site shows a cross section without it. But for a cooler type setup.

What's a novice to do? ha.

Is this the paper gasket between the filter cover and the engine case? If so, and with a canister depth of 3.1mm, then you really don't need the gasket. Realize that the true sealing of the filter cavity is done with the large white o-ring. Provided you have the right amount of compression on the white o-ring, in the neighborhood of 15-25%, then no gasket is needed. If the canister depth is much less than 3.1mm, then you need a gasket but only as a spacer...the gasket moves the cover out the amount equal to the thickness, thus reducing the o-ring compression. If the canister depth is much greater than 3.1mm, say over 3.5mm, then you still don't need a gasket but likely will need more than one metal shim against the canister sharp outer edge. The additional shim is needed to increase the compression on the o-ring because the canister edge is too deep.

Here is a past thread where the issue is discussed relative to the gasket and/or shims:

https://forums.bmwmoa.org/showthread.php?33334-Confused-about-the-2000-O-ring

Here's my pictorial for a /7 filter change:

https://forums.bmwmoa.org/showthread.php?95493-R100-7-Filter-Change-A-Pictorial

20774 said:

Is this the paper gasket between the filter cover and the engine case? If so, and with a canister depth of 3.1mm, then you really don't need the gasket.

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Many many thanks Kurt. Yes, that is correct. The EV diagrams all show the gasket being used. Hence my unknowingness.

Along the lines of what you've described, I was headed in the direction of not using the gasket. Your reply was very helpful, thank you.

Finished the swap this morning. "Felt" alright all going together. Thank you's to all that weighed in. Greatly appreciated.

Well, you're somewhere between 27-30% compressed on the white o-ring according to Oak's computations. Might be a tad higher than he might have wanted. If a gasket was used, then the compression would have been about 18%...probably somewhere in the middle. When you take this apart for the next oil change, inspect the white o-ring. It should be in the form of a square, but if you find severely mangled or split, I'd go back to using a gasket.

20774 said:

Well, you're somewhere between 27-30% compressed on the white o-ring according to Oak's computations. Might be a tad higher than he might have wanted. If a gasket was used, then the compression would have been about 18%...probably somewhere in the middle. When you take this apart for the next oil change, inspect the white o-ring. It should be in the form of a square, but if you find severely mangled or split, I'd go back to using a gasket.

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Thank you Kurt. Do you think it be better to remove the cover and install the paper gasket then under these circumstances?

I don't know...it would be nice for Anton to weigh in. I'm just looking at this page on this http://largiader.com/tech/filters/canister.html On the right side it shows info for the sharp edge canister which I assume you have. I think you get your canister depth, which is 3.1 from the left column. Read across to find that the presence of a gasket adds 0.45 so now we're at 3.55mm. Then adding the shim reduces that back to 3.25mm which he shows as the "groove depth" on the right side. He says to target a groove depth of 3.3mm. So that configuration is nearly on the money. If however, you leave out the gasket, the groove depth drops to 2.8mm. The ratio of 2.8 to 4.0 (which is the original thickness of the o-ring) is 0.7 or basically the thickness has been reduced by 30%. It's not overly high but beyond the typical numbers. Anton says it's not "rocket science"...maybe I'm interpreting his chart wrong.

I suppose installing a gasket could be done without making a mess! Lean the bike over on the left side so that when the cover is removed, no oil should drain out.

One thing that I've been doing after installation of the oil filter. I drop the float bowls and hit the starter to crank the engine. I keep cranking until I see the oil pressure light go out. That way I know that the oil system is completely filled and the bike won't start "dry" the next time.

STEVENRANKIN said:

I had an oil cooler on my RS and got rid of it. Unless you are riding in extremely hot conditions, you don't need one.

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Total misunderstanding.

It's somewhat well known that the big valve R100s produced through 1984 (USA availability) suffered from warped cylinder heads because there was not enough material left to prevent it.

The oil cooler is a defense against this warping.

For R100GS and the return of RS and RT in 1987, BMW only fitted small valve (32 versus 40) cylinder heads.

The oil cooler on models equipped with thermostat only functions when engine temperature rises to a certain level and this has almost nothing to do with ambient temperature. Rather the hottest an aircooled engine gets is when it is running at high rpms and doing significant work and consequently burning most fuel. Simple ... burn more fuel, create more heat. As we know, aerodynamic drag increases at the square of speed increase (4 times the drag of 50 mph at 100 mph) and a BMW at 100+ mph is pretty "draggy" and of course a lot of power and consequently fuel burn is required to achieve this speed. It's clear from my 20+ years experience with my 1984 RS that indeed the oil cooler is only ever used at highway speeds.

Don't forget, BMWs are made first and foremost for German conditions, which can mean high speed Autobahn running.

Many of us (ahem) older guys remember USA bangers that had their radiator fan directly attached to the water pump ... a situation where when idling around town, for example, there was little water circulated through the radiator and of course there was little airflow through it and therefore overheating occurred. Things are apples/oranges different with aircooled BMW motorcycles and old ideas are not applicable. For the most part engine heating on these bikes is directly proportional to fuel burned. Also, remember, that 100 degress ambient temperature, is really cool compared to the engine temperatures created by fuel burn and consequently has little effect. I have not seen it in print for Airheads, but I have an early Oilhead service manual, where the user is cautioned not to allow the engine to idle for more than 20 minutes. That's a pretty long time, and indicates quite a bit of cooling capacity is inherent in the finning and that model's oil cooler and 4-valve heads. So, if you're idling a bit, you're doing the exact wrong thing to blip the throttle or increase rpm. You don't have a water pump to speed up and all you're doing is burning more fuel and creating more heat.

So, if the original poster is only going to toodle around town on his RT and never hit the highway, he will be ok deleting the oil cooler. Otherwise, it's a bad idea. And of course always always always, if you're concerned about heat, run full synthetic motor oil.

lkchris said:

So, if the original poster is only going to toodle around town on his RT and never hit the highway, he will be ok deleting the oil cooler. Otherwise, it's a bad idea. And of course always always always, if you're concerned about heat, run full synthetic motor oil.

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Thank you Kent, that was most informative. As a final note regarding the oil cooler delete, this BMW once running again will be on a fully synthetic diet. Cruising around town will be it's biggest challenge. Not necessarily much high/extended rpm touring.

I greatly appreciate the information you've shared.

20774 said:

I don't know...it would be nice for Anton to weigh in. I'm just looking at this page on this http://largiader.com/tech/filters/canister.html On the right side it shows info for the sharp edge canister which I assume you have. I think you get your canister depth, which is 3.1 from the left column. Read across to find that the presence of a gasket adds 0.45 so now we're at 3.55mm. Then adding the shim reduces that back to 3.25mm which he shows as the "groove depth" on the right side. He says to target a groove depth of 3.3mm. So that configuration is nearly on the money. If however, you leave out the gasket, the groove depth drops to 2.8mm. The ratio of 2.8 to 4.0 (which is the original thickness of the o-ring) is 0.7 or basically the thickness has been reduced by 30%. It's not overly high but beyond the typical numbers. Anton says it's not "rocket science"...maybe I'm interpreting his chart wrong.

I suppose installing a gasket could be done without making a mess! Lean the bike over on the left side so that when the cover is removed, no oil should drain out.

One thing that I've been doing after installation of the oil filter. I drop the float bowls and hit the starter to crank the engine. I keep cranking until I see the oil pressure light go out. That way I know that the oil system is completely filled and the bike won't start "dry" the next time.

Click to expand...

Thank you Kurt, lucky for me I have not refilled the oil... So I may add the gasket back in. I mistakenly looked at the 'round edge' guidelines, should have been more careful.

Strange

In all the years I have been riding airhead BMW bikes and haunting at first my local dealer then dedicated airhead repair shop, of all the hundreds of airheads I have come across, only three had oil coolers on them and both of us owners took them off. The one owner being a BMW airhead trained mechanic (who took the bike to Germany for a summer and rode it hard).

I am sorry, I have never heard of the 70's big valve head bikes having warping problems, I have never seen a set of warped heads ever come into the shop either. My understanding of BMW's change to smaller valve heads was to meet the tightening emission standards being introduced as well as the change over from leaded to unleaded gas fiasco.

It makes no sense to me to detune an engine when an oil cooler could have been used to solve a problem. A cooler doesn't really need to be complex or need a thermostat to protect at high heat levels, just the radiator. So the cost to install a simple radiator I would think would be far less than redesign and retooling for smaller head bikes. If in fact warped heads were a problem and the oil cooler the solution.

Personally, I have never had anyone I know who rode or rides a 70's era large valve BMW airhead have a warped head. I have never seen a warped head come into my friend's shop. I have experienced bad valve seats and other BMW nonsense.

Given a choice between a 95 R100RS and my 78 R100RS, I am here to say, I will take the 78 engine over the 95. I personally have not seen any improvement in reliability from the 78 model to the 95 and I can feel the lack of HP and torque in the 95.

BMW had the right engine back in 77/79, forces outside the company forced them to make changes as well as the never ending search to build things cheaper so as to make more money. St.

I personally would not remove the oil cooler. It was put on the bike for a reason. If it has a properly working thermostat it will help the life of your engine. Oil temps need to be kept below about 250 F for conventional oil to survive. The oil cooler makes that possible. The airheads didn't have a very large oil capacity, so keeping the oil temps within a reasonable range is important.

Much has been written on the white O ring and gasket, so do your homework and some searching. The white O ring has to be shimmed properly for it not to leak.

STEVENRANKIN said:

I am sorry, I have never heard of the 70's big valve head bikes having warping problems, I have never seen a set of warped heads ever come into the shop either.

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Oak related the problem.

So

OKAY, I respect Oak, and many other BMW gurus, I guess he acknowledged BMW engineers made a mistake and he and they suggested a fix in way of an oil cooler. Great, it still doesn't answer the question logically, when a simple oil cooler could have been installed on all the bikes, but as to my knowledge first hand by observation of bikes owned by friends and customers of my local shop to solve the problems, why did BMW change over to the smaller valves and detune the engines?

Even the "experts" can get it wrong sometime. I recall a lecture by one such person relating how he spent a summer "upgrading" the performance of his airhead only to find out he was wrong and the whole project was a waste of time. Since even "experts" make mistakes and errors, I always look at their advice with my experience as a balance to decide what is works for me. I must be doing something right because I have two airheads with 300K miles between them. And my best friend has a 79 RT with over 200K. I also know others with 78, to 80 bikes without oil coolers who have fairly high mileage on their bikes with no coolers.

I could be 100% wrong about oil coolers, as well as a lot of things I write about I am far from perfect in knowlege. Perhaps, someone could produce a BMW memo or some kind of BMW document relating to the problem and its solution specifying an oil cooler addition as a solution to an existing problem?

If I see it from BMW the call for an oil cooler to fix a problem, I might be willing to re install my cooler or leave it off with the knowledge a potential problem with warped heads might occur.

So far, I have a lot of miles on my 78RS with big valve heads, my friends have lots of miles on their 79RTs and we have not had any problems caused by getting rid of the oil coolers or never having a cooler. The only thing in all fairness I have gained is a slight ease in oil filter changes and one less part to go wrong meaning the thermostat. St.

Temps Reduced By Oil Cooler

I'd be curious how many degrees are reduced with oil cooler in place. A dipstick mounted thermometer would make a good measuring device. My guess, maybe 5-10F. Especially with the wimpy little OEM cooler on Airheads.

Of the six Airheads I've owned, three were RTs, and all three had air coolers. The 79 and 82 RTs had problems with unacceptable exhaust valve clearance loss rate. Interestingly, none of the three other Airhead (78 R100/7, 79 R65 and 76 R90/6), nor the current 95 R100RT, had the valve problem. I doubt fairings were a factor, since the four other bikes also had fairings (Luftmeister w/lowers, Pichler, Hannigan and RT). I believe the difference is at least partly due to the smaller intake valves. Of the six Airheads, only the two with large valves had the valve problem, though they both had oil coolers.

If seriously wanting to reduce oil temp, I'd install a much larger cooler, or maybe two of them. Probably hung off the safety bar(s), with manual on/off valve instead of thermostat. Not worried about oil temps though; I rode two of the Airheads (78 R100/7 and 79 RT)in the California desert quite a bit while living there, and no problems with oil breakdown. Back then I used Castrol 20w50.