Tech Question

[FixerDave]

Hi,

my ’90 KLR650 has been running hotter and hotter over the last few years. It's not actually overheated... not yet anyway. But, it is getting to the point where I'm noticing the power loss at times. The fan is pretty well on during anything but highway cruising… down hill, on a cool day.

I've tried everything... I've re-jetted it significantly richer, I've checked over the entire cooling system including the impeller and it's all squeaky clean with nothing worn, I've changed the plug, the carb looks great, and the valves are in spec, though one is close to the edge and on my to-do list.

Right now, I'm running cool-max instead of antifreeze and it's keeping it tolerable. But... I'd really like to figure this out.

What really bugs me is that I've had the same problem on my last 3 bikes. The previous 2 were air-cooled Hondas (XR250 and XL350) and it was the reason I bought the water-cooled KLR. I swore I'd never go through that again. Maybe, it's just a coincidence… or maybe it’s something I’m doing??? It’s such a weird problem.

Has anyone else gone through this?
Am I the only one?
Any suggestions for what to check next?

I consider myself to be a competent mechanic… I rebuild engines for fun… but this overheating problem is really starting to irritate me.

David...

[bmw rocke]

I know this sounds stupid and I don't want to insult you but... Another person was having a overheating problem with his KLR and it turned out to be years worth of dirt and bugs built up in the rads. He used some de-greaser and washed the rads out and the bike stopped overheating. I mean wash the outside of the rads to make sure that air can pass easily. Sounds simple but it's worth a try. Rocke

[Pirate]

You sure are aptly named Fixerdave....Here's a couple of things to check. Make sure that the rad has all the cooling fins intact and in good condition otherwise she will cook and also check the thermostat is working correctly. You could remove it just for the test, but don't remove it permenantly...........Good luck!

Pirate........

[FixerDave]

yes, I've sat there with a pair of tweezers straightening out each individual bent radiator fin, making sure they weren't blocked in the process. It helped a little but didn't put it back to anywhere near what I would expect.

I never thought about using a degreaser though... I've just shot it with water or blown the dust out with air. It doesn't look plugged up but maybe some soap might help???

As for the thermostat... I've never thought of running without it to see what would happen. I've made sure it opened and it looks squeaky clean. I'll try that next. Thanks.

David...

[Sabre]

Dave,

This won't directly address the gradual change you're seeing with your KLR, but anything to eke out optimal cooling might be to your advantage.

Have a look here: http://klr6500.tripod.com/radiatorcoolingmod.htm

Other ideas: no air leaks on the intake side? Pipe lost its packing or changed pipes? Any scale or buildup that would decrease the flow through your rad?

I'd suspect a faulty guage or sender unit, but you're reporting actual perceptible power losses. Puzzling...that shouldn't occur until you're WAY overheated. There is a tremendous variability in what those guages read from bike to bike, or in the same bike over time; is it really getting hotter?

[FixerDave]

interesting website... and interesting modification. I'll try that irrespective of how the thermostat test works out. Thanks for sharing the site URL.

As for the rest... I've checked and double-checked. No scale at all and the intake side seems quite well sealed. Out of deperation, I even tried a wee bit of silicone around the intake seals. Also, I rejetted the bike to see if that would help. At the same time, I added a K&N filter... just because, but I know that's not the problem because it started well before that. Seeing as how my range dropped from 330km to 220km, I can't imagine that it's still running lean. It's not blubbering rich though. The exhaust is still stock. The plug always looks a perfect tan.

If it isn't the thermostat then I'm going to weld an oxygen sensor bung on my exhaust pipe and absolutely undeniably confirm that the bike is not running lean at any point. (I did that when I tuned the quadrajet in my van, worked like a charm.) I agree with you, it sounds like the bike is slowly leaning out but everything I check in the carb etc. looks fine, before and after I've cleaned them anyway.

And yes, it's running hotter. When I'm wrestling the bike in the single-track and the guage gets well past the halfway mark, I notice the blubbering and poor response. Like I've said, I've been through this before with my previous 2 bikes. I know what overheating feels like. It's not enough to stop me from riding, yet, but I know it's not right.

As a side note, the previous two bikes were both RFVC Hondas ('84 XR250 and XL350) that I had at the same time. Back then, I just thought it was some quirk of the Honda engines... they were pretty well identical except for the displacement (4 valve dual carb singles). Now that the KLR is going down the same path, I'm starting to doubt myself... wondering what I'm missing.

Anyway, worst case I'll do that radiator mod and buy myself another year. Thanks for that.

David...

[joker650]

Check that your muffler has not fallen appart on the inside causing a restriction. This WILL cause overheating, and can happen slowly over the years.

[FixerDave]

A restricted muffler... now that has never occurred to me. It doesn't quite fit the symptoms though. It doesn't feel stuffed up and it revs out quite well. Further, it overheats less when run "aggressively" which I've attributed to greater coolent flow from the higher RPMs. If it was plugged, I'd expect the bike to crap out at higher revs.

In any event, short of replacing the whole thing, how am I suppose to check it? It's a sealed unit; it doesn't even have the little cleaning cover that the shop manual says it should. I don't even have any idea what the stock mufflers look like inside... other than it's suppose to be mechanically baffled. Is there a spark arrestor screen? You've got me thinking now, thanks.

David...

[islandswede]

Sounds like you've done your cooling work, but I don't think I've seen any reference to the waterpump?

Other issues you might want to explore is ignition timing, compression test and valve adjustments and timing. These are all common overheating issues in low tech engines such as the KLR, especially when warm.

For whatever it is worth, my old Volvo boat motor had the same type of problems until I rebuilt the head and got the timing accurate.

Good Luck

[joker650]

In any event, short of replacing the whole thing, how am I suppose to check it? It's a sealed unit; it doesn't even have the little cleaning cover that the shop manual says it should. I don't even have any idea what the stock mufflers look like inside... other than it's suppose to be mechanically baffled. Is there a spark arrestor screen? You've got me thinking now, thanks.





Well it may not be the problem. But I have herd from a coupl other guys with KLR's that have had the screen at just inside the "Out Hole" break loose and plug up the exit.:mb:hehe.....

But the waterpump could also have low flow.

Check the muffler for a blockage. If it looks good remove the thermostat and go out for a good hard ride, some tight bush stuff where the eng is really working(all this WITH coolant of course). If the overheating is still present (and your rads are clean inside and out) you will need a new waterpump. If the eng does not overheat, replace the thermostat.

DO NOT USE SILICONE TO SEAL THE COOLING SYSTEM!

[FixerDave]

Yes, I have already bought a replacement water pump impeller, even though the original looked fine. It measured out at near exactly the same size as the installed one -- there is no discernable wear. I actually didn't bother putting the replacement impeller in as, well, I sort of forgot to order the rear seal that goes with it. I don't think it's the impeller.

Ignition timing... I seem to recall checking that once, a while back, but I suppose it's worth another check.

Valve timing? Well, maybe I'm getting slack in the chain, or maybe things get a little upset near the edges of the valve adjustment range... I am due for an adjustment there as one valve is near the limit.

I'll start with the muffler, try the thermostat, and by then it will be mid-August and time to adjust the valves. Thanks for the ideas on where to look.

But, I have to ask... why not use silicone? I've never heard of problems with silicone around a cooling system. I've certainly seen enough of it while stripping down Chev 350s.

David...

[joker650]

But, I have to ask... why not use silicone? I've never heard of problems with silicone around a cooling system. I've certainly seen enough of it while stripping down Chev 350s.



Well yes people use it on car/truck engines( But I don't see the reason because everything has gaskets). But on a bike I just think that the cooling system has some verry small ports and if you use too much something may get plugged. Silicone can cause BIG problems on engines.

Just use the supplied gaskets unless the manufacturer calls for some type of sealant.

[Land Shark]

Hey Fixer:

I'm curios to know if the rad fan kicks in when the bike gets hot? It should. And if it runs hot, the fan should be on all the time, or until it cools after shut down.

I'll look in the Clymer manual tonight and see if any thing is mentioned about overheating. Then I'll post what response they have if any.

Land Shark

[FixerDave]

Yup, the fan's on almost all the time.

David...

[Land Shark]

Allright Fixer, here goes...

Engine Overheating

Engine overheating can occur when the motorcycle is operated at slow speed at high RPM. This can occur in severe offroad riding conditions. Even though the fan turns on, excessive heat build up can cause the engine to overheat. When this occurs, stop and allow the engine to cool. If overheating continues after the bike is ridden at moderate speeds and lower rpm, check the motorcycle and determine the cause of overheating.

In otherwords, your having way too much fun....

With that said, here's what to check. And as always, check the most simple things out first before tearing the rad out to find it was a clogged fuel tank cap vent hose.

Cooling System

a. Coolant level low.

b. Water in system, no coolant mix.

c. Air in system. (probably hot desert air !)

d. Radiator clogged.

e. Radiator cap damaged.

f. Thermostat damaged.

g. Fan fuse blown. (not likely in fixers case as the fan is always on)

h. Fan relay or switch faulty.

i. Fan shaft seized.

j. Water pump impeller loose.

k. Water pump impeller damaged.

l. Water temperature sending unit faulty.

m. Water temperature gauge faulty.



Engine

a. excessive idling.

b. Insufficient oil level or viscosity.

c. Incorrect spark plug heat range.

d. Clogged crankcase oil strainer.

e. excessive carbon buildup on piston / cylinder head.

Fuel System (Causing lean fuel mixture)

a. Clogged or pinched fuel tank cap vent hose.

b.Air leaks at intake duct.

c. Wrong pilot or main jet for altitude.

d. Clogged carburetor jets.

e. Float level too low.

Ignition

a. Improper spark plug heat range.

b. Damaged exciter coil or ignition pickup coil (check ignition timing).

Now that'll keep ya busy for a moment or two, eh! He he he....

Land Shark

[10guy]

try using a 70/30 mix of antifreeze. water conducts heat much better than anti freeze or conversely, antifreeze is a poor conductor of heat. you should notice a result from this. I mixed my coolant @ 50/50 and i noticed right away that the bike runs MUCH hotter than normal. so i'll have to do a remix...

Good Luck.

[FixerDave]

Odd... I didn't get the email notifications... sorry for the delay in responding.

c. Incorrect spark plug heat range.
I've been wondering about this. I do have the "correct" plug, and I've replaced it just in case, but I've considered experimenting with cooler plugs. Never have actually tried though.

d. Clogged crankcase oil strainer.
Now this has never occurred to me. I hope it's not the problem... kind of scary to think about actually.

For coolant, I'm running coolmax and water, no antifreeze at all.

As for my riding style, it actually runs cooler when I'm really pushing it... which, oddly enough, is a whole lot of the time :)

Anyway, thanks for all the advice. It will keep me going for, probably, most of this year.

David...

Could be the rad cap. If a new cap is cheap, try that.

You could also try running the bike without the rad shrouds and see if that makes a difference.


Not sure if bike shops have it but I remember automotive shops having a rad cap pressure tester.

[MarkStH]

Sabre wrote:
Have a look here: http://klr6500.tripod.com/radiatorcoolingmod.htm
Hi everybody! I was looking for information on my own weird problem and came across the above link. That site is old and hasn't been updated for quite a while.
The new site, with much more content, current content, is here: http://www.klr650.marknet.us (http://www.klr650.marknet.us)
That cooling mod is here: http://www.klr650.marknet.us/radiatorcoolingmod.html
Best Regards, Mark