Ideling an engine too long without use of fan

I have read a lot that you should not let your engine idle longer than a few minutes without the use of a fan. I do understand the concept and thought behind that advice , but here comes my question. Have the engines not been designed to withstand ideling for a longer period of time like it may occur in a traffic jam? What are you guys doing if you come to a standstill somewhere on the highway?

Lane splitting is legal in some states, but if it looks like the traffic won't be moving for a long time I make like a moped and use the shoulder.

When I am working on the bike and need to have it idle I'm careful of this issue. It gets hot, I don't have a fan available, but it seems to do just fine. I probably don't idle the bike more than 4 mins in these situations.

I've had a couple of times in traffic though that were disconcerting. In the city I have been able to take a different route but several times stuck on some Highway the bike did seem to be too hot. I've adopted the attitude more recently that I have to use the breakdown lane and I either go to the nearest exit or if I know what roads are around I select an exit near by.

The bike runs very poorly when it gets this hot but apparently it's not been a lasting issue as it seems to recover. There have been recent threads about riders that have warped heads or valve covers and these could be from such over heating episodes.

Depends on the various circumstances.

Has the bike just been started from cold.
Is the engine already hot from slow driving in traffic/trail work.
How long do you expect to be stopped for.

If I catch a red light at a known slow changing intersection on a hot day, I switch off. Why sit there for 90 seconds idling an already hot motor.

I've idled them longer than four minutes, sometimes when there's been trouble adjusting carbs. And then the hotter it gets, the more likely you'll have to go back and tweak things when it's at normal running temp.

It depends a lot on how hot it is that day. But the thing to be concerned about the most is the cylinder heads. They're the hottest part of the engine.

I too have found it almost amusing that airhead riders don't think they can idle these engines for more than a few minutes without assistance from fans. Do you really think that in all the time BMW spent developing and building these engines they considered that sometimes the traffic stops moving. When you compare other air cooled configurations such as the UJM 4 cylinders the airhead is a much better design for cooling itself. I never shut any of my bikes off on the highway when stopped at construction or traffic delays without any problems. These things are not fragile, they can handle idling just fine. On tuneups and settings I can see where holding the cylinder head temperature stable would be important but outside of that I don't see it.

I have a question on how you would cool the jugs if more than a couple minutes. Would you use 2 fans, 1 on each cylinder? Just wondering.

I would think even a slight breeze will be enough to keep fresh air moving over the cylinders. Now if it's dead still, like in a garage then that's a different story.

+1

That's a bit more than necessary but would work.

I usually put my one box fan in front of the front wheel and crank it to medium or high speed. Provides plenty of air over the cylinders.

Anything more than 10 mins. on the fan and I just hop on for a spin around the block. This also helps me tell how close my adjustments are getting.

A large % of BMW production has always been for Government service and as such those bikes would have spent quits a bit of their time sitting in slow moving traffic.

Where I live is not that warm, but I don't bother with fans when playing with carbs

FWIW: I have been sitting with a 1000cc CR9.5 engine in stop 'n go traffic for more than 1/2hr on the motorway at high noon during a very hot summer day (deliberately not using the shoulder to drive on). The oil temperatures (no oilcooler) measured at the oil dipstick went way into the red zone for most of the time (way past 260F IIRC) and I was getting nervous. I was about to use the shoulder and shut the engine down (got cold feet I guess) when traffic moved on. Everything went back to normal soon after.

They can idle for a very long time. I have not used a fan when setting carbs.

There was a thread on this forum I think, where someone had started up an airhead and forgot about it, until it ran out of fuel, what I can't remember was how much damage was caused by this.

I have in the past ridden at slow speeds in deep ish sand at air temperatures in the 40-45C range in the middle of Australia, the oil temperature did get into the red zone, but I don't think any real damage was caused.

I've recently experience when stuck in a traffic jam that my idling gets higher and after more than half an hour on really slow traffic in the tropics, the idling goes up to 4000 rpm... After turning off the engine and giving it some rest, it's starts and idle normal again.... Any reason why it's like this?

My own experience over almost 40 years of riding and self-maintaining my BMWs, has been to use common sense. If I am in traffic that is running extremely slow on a warm to hot day, then you may need to pull over and let things cool down, or find another route. Basically, if when sitting on the bike and the heat from the cylinders is getting very uncomfortable for your shins, then it is getting too hot. Pulling over and stopping, may not be the best thing to do, as the heat will continue to build for a short while after shutdown. If you can, pull over to side of road and just putter along, keeping the air flow happening. Better yet, get out of the traffic and ride a different route till the bike cools down. Only takes a few minutes.

As to tuning carbs, I have never bothered with a fan. I have had stock bikes idling for up to 15 to 20 minutes with no ill effects. I say no ill effects because those same bikes are still on the road with a lot of mileage on them and most have never had any major work required. I figure that if I can get over 200,000 miles, or more, on an engine without a rebuild, then no real damage has been done by letting them idle like that.

Plus, if you take longer than 15-20 minutes to set carbs, then you have other issues involved. These bikes are so damn simple, you should be able to get the carbs pretty close prior to initial startup then it just takes some minor tweaking. But many people keep looking for a fix, where there isn't any real problem.

So, can anyone quantify what too hot is? If I put a temp gauge on the heads what is the max temp before damage occurs? I have an oil temp gauge in my pan (cooler than heads I'm sure). Sometimes during very hard riding it can get into the 265 F range.
Normal riding (for me) is around 190 to 205 F. Is oil pressure more important than temp?

The two go hand in hand. As oil gets hotter, it loses viscosity. As it loses viscosity oil is able to flow more easily through tight spaces and puts less back pressure on your oil pump, resulting in a loss of oil pressure. It's ALLLLLLLLL related.

Obviously, let me clarify, a good oil pump will produce more pressure than a warn out one when hot. 50 lbs of pressure at 300F has to be better than 10Lbs at 300F or 10Lbs at 180F for that matter....right?
At some point the oil is just too hot no matter what pressure it's at. I just want to know how hot that is?
Or is it that the expansion of some internal parts will become so great that no amount of lubrication will prevent seisure?

I would expect an Airhead to be far better than a normal aircooled bike for extended idling. Those cyls sticking out there with vertical fins, hot air rises and all that stuff. On a normal bike with vertical engine and the a tank above the engine and horizontal fins there could be problems - but I've given normal bikes a hard time in that department with no problems. I'd be complaining to the manufacturer if my airhead overheated more than some cheap nasty bike.

Your most critical bearings, mains and big ends, depend on an oil film to prevent metal on metal contact. As your oil gets hotter and loses viscosity it loses it's ability to resist the pressure of a rod being forced into a crank journal by combustion pressure. At what exact temperature this occurs depends on your oil formulation and how much load the engine is under. I won't even venture a guess because I have no idea. No amount of oil pressure will prevent this if the oil is not viscous enough.