TRF Forums

As per the title really, air cooled engines must be susceptible to overheating doing trail stuff...how does one who is not so familiar with a hot air cooled engine, listen, hear, feel or smell when the engine is getting over worked and ready to pop? Can temperature monitors be installed in the fins with a monitor on the bars and maybe a red warning light when it's getting too hot?

Also what should I do if I suspect overheating, I suppose initial reactions may be to turn off but is it better just to let it tick over to allow the oil to dissipate heat?

Many thanks

Ash

I would check the plug colour to see if it's running lean and hence hot. Spit on the fins and see if it hisses and boils off.

If you smell burning leg, that's often a giveaway.

you can get an oil temp gauge to replace fill plugs if you are worried, the oil cools as much as the air. Use a good quality semi synthetic oil and change regularly. Just ride and enjoy it, air cooled engines run bigger clearances to accommodate temp variations.

Sochiro Honda was resistant to water cooling for many years...the water gets in the way, he said.

Here's why...

The reason water-cooled bikes overheat is there isn't much of a temperature gradient between 110 C (which is as hot as a water-based coolant can get in a pressurised cooling system before it boils) and ambient temperature.

There's a huge gradient between engine operating temperatures and ambient temperatures, so even a hot air-cooled engine will keep cooling itself. Dry sump bikes can also dump heat from the engine oil as it circulates to the tank or frame.

You might overheat the clutch, which will be evidenced by clutch drag.

If you think the engine is getting too hot, then keep the bike moving, the oil circulating and the air flowing over those fins.

I never overheated my DR350S...not in heavy mud in the UK, and not in deep sand in Africa.

Be glad that you have an air-cooled bike...Suzuki DR250/350s rock!

Radiators and hoses can crack, split, puncture or just start leaking for no reason at all.

No water, no worries.

You forgot water pumps and their woes/corrosion

All my bikes are air cooled and they work fine

Thanks to bill and spink. Spink....you're name is hard to type without auto correct on my iPad wishing to type spunk!

Any way, Richard, you're response whets my whistle for technical know how.....

To simplify, or to check my understanding, a sealed water cooled system cannot exceed 110 degrees and is finite in its volume whereas air cooled has an infinite quantity of air around it that will heat up to/manage any temperature and dissipate even white hot metal heat rapidly (heat gradient) to the air.

I felt I had been riding the clutch a lot on my first outing as I was tentatively negotiating icy rocks etc and getting stuck a lot. Twice when I came to a stop pulled clutch in and She stalled as if I just stopped in first, I assume that was the clutch sticking due to excess heat. Both occasions were very shortly after riding it like a bitch (for want of better terminology) to get out an ice pit etc.....

If that's happening with the clutch I assume I'm shortening the lifespan as heat and longevity don't tent to mix, again is there anything I can do to minimise clutch damage and what is happening then that causes it to stick, I assume the plates bond or the bearings get a bit tight with heat?

Many thanks

Ash

Going back some years to my yammy fiss bomb (FS1E) i remember it getting too hot, early signs were a pinging noise followed by decreasing power and finally locking up.

That's about it....old Brit bikes used to overheat sometimes but they had cast iron barrels and not much in the way of fins.

The DR350 had an oil jet directed at the underside of the piston crown specifically to cool the hottest part of the engine: I expect the 250 is the same.

It's friction rather than engine heat which is making your clutch drag...expansion and sticky oil as much as anything.

You can in ascending order of difficulty:

1) Adjust cable freeplay at the lever to restore manufacturers specs. Do this first with the engine cold, then adjust again if the clutch starts dragging in the field.

2) Change the oil: thick 'used' oil has carbon and clutch debris in it that make the clutch drag.

3) Strip the clutch and wash the friction plates in water, dry and reassemble.

4) Inspect the 'fingers' on the clutch basket and carefully remove any indentations which may catch the ears on the plates

5) Drill small holes in the clutch basket to improve the flow of oil.


Or, it may be that you bike is geared too high for trail use. You can buy alternative size sprockets front and rear to raise or lower overall gearing. Going down one tooth on the output sprocket is about the same as going up three teeth on the rear wheel sprocket. Tallon, Renthal etc make sprockets with different tooth numbers for most bikes.

Ash,

As others have said use good quality motorcycle specific oils, clean gauze strainer filter and change your replaceable filter regularly. I do two oil changes to one filter change on my Serow.

In the past I have had four stroke engines with their exhaust header pipes glowing cherry red with no adverse problems with the engine. Occasionally I have flicked the choke on/off repeatedly to richen the mixture so to cool valve faces/seats.

A 'Pinking' sound on acceleration when not normally experienced will give a clue to impending problems. Just try to get the bike moving in free air as soon as possible. Anyway getting them hot occasionally boils off any water vapour that might be collecting in the cooler parts and in the breather system.

TTFN

Hugh.

Luddites.... The future is liquid, and cool....