ST1100 Overheating Enigma

[dwalby]

I agree with UP, if they're fairly slow leaks the temperature shouldn't climb that high so the radiator would be the prime suspect on the overheating issue. If the fan comes on and the needle keeps rising, then that's a good clue the radiator isn't doing its job. But given that you had Bars Leak throughout the system, anything is possible I guess. The T-stat could also be limiting flow, so change that too.

there are used radiators on ebay, with 30-day return policy, for relatively cheap. Some include the T-stat housing, overflow tank, etc. Might be worth it to replace yours as the first step, then figure out where all those leaks are coming from. Its a bit of a crapshoot going with used parts, but if they'll take it back if it has any issues you have nothing to lose. Use a credit card on the purchase, screenshot the return policy, and if push comes to shove later your cc company should back you up on a refund.

 

[SMSW]

Back in the day (when radiators were made of brass and copper), radiator shops would remove (unsolder) the top and bottom 'pans' from the radiator core and 'rod out' the passages. This meant they pushed a rod w/ bristles down each core to clean them out. If a few tubes were leaking, they were plugged with solder at the top and bottom. This was, of course, labor intensive and has gone the way of the great auk...you cannot unsolder the top and bottom of an aluminum radiator.

I've never used any of the stop leak formulations figuring that somewhere inside the engine there was a small passage that said stop-leak would plug up, to the detriment of the cooling system. I suppose they were designed for use in big old cast iron engines with large cooling system passageways. Bars Leak probably has fine print on the bottle saying something to the effect that they are not responsible for anything. Back in that day noted above, the old guys also said to use thick potato soup as a stop leak. I suppose when traveling cross country and you ran out of food, you could just tap the radiator for a cup'o soup.

Alas, buying parts on ebay is, as @dwalby said, a crapshoot. And most of the places I've seen say they will cheerfully refund your money but you pay to ship the item back, even if you test it as defective. You might win if you pay via paypal and the vendor says it was good when it left their shop, but it might not be worth the hassle.

 

[Larry Fine]

Check/replace the radiator cap.

 

[Erdoc48]

Check/replace the radiator cap.

This is always a good, less expensive, less energy intensive to fix idea as well. I had some minor higher heating issues with my ST in the past (so I changed them on both STs) and a new cap cured it (I guess I was losing coolant via the cap that wasn’t holding pressure as well as it normally would have.

 

[Gman]

I had a radiator that did not flow good enough.

When I removed it and tested with a water hose it seemed fine however it wasn't good enough. I had a known good radiator and it flowed only slightly better, I tested them side by side ..... however it fixed the overheating problem.

My bike did not overheat in 3 minutes, it took about 15 minutes before it would get to the hot mark.

Also when you drained and changed the radiator coolant, was it just water or was it coolant that was drained and was it rusty?

Good luck.

When I first drained the coolant it looked fresh as a daisy. But now that I think about it the first time I rode it and before putting Bars Leaks in it, it overheated right away. Might a commercial radiator cleaner do any good?

 

[Gman]

I would probably drain the coolant out and see what it looks like.
Be sure on the refill you use the proper type of coolant - wrong one can wreck the water pump.
As MotorBikeMike pointed out you can get flow but not enough in the radiator to get properly cooled.
I had the same problem on one of mine as he did and it turned out to be the radiator was partially blocked.
Where does the temp gauge get to - over in the red?
Checking the overflow tube as Kiltman said can also be the culprit.
The fan should have kicked on before it got to the red if the fan it working.
Test it by grounding it - wire is on the sensor on the lower left back side of the radiator.
If it comes on when grounded but not when the engine is hot, you've got a wire problem or a sensor problem.

I tested the original fan switch by boiling it on the stove with meter attached. It didn't close. Bought a new one and tested it before installing. It closed a little before boiling. Installed it but the fan still did not come on. Fan works when grounded. Can't understand this. Will test new switch again. Repaired the overflow tube early on.

 

[Uncle Phil]

I tested the original fan switch by boiling it on the stove with meter attached. It didn't close. Bought a new one and tested it before installing. It closed a little before boiling. Installed it but the fan still did not come on. Fan works when grounded. Can't understand this. Will test new switch again. Repaired the overflow tube early on.

If you ground the wire that goes from the sensor (lower left bottom of the radiator) to the fan and the fan kicks on, that says the wiring is fine.
It could be not enough coolant is not reaching the 'probe' of the switch.
If the coolant level is low it will not turn on the fan.
I don't understand the 'close' reply since IIRC it is just an element stuck in the radiator and the connector for the wire.
Are you by chance talking about the thermostat and not the fan switch?

 

[ST1100Y]

It could be not enough coolant is not reaching the 'probe' of the switch.

Indeed, if the system is leaking/low, it won't pressurize, the temp probe on the top sees only steam, hence the gauge will indicate "HOT" (or the system even "boils") long before the fan stat reaches sufficient temps to switch the fan on...

 

[John OoSTerhuis]

Replace the radiator, fix the coolant leaks, and go ride!

 

[Gman]

If you ground the wire that goes from the sensor (lower left bottom of the radiator) to the fan and the fan kicks on, that says the wiring is fine.
It could be not enough coolant is not reaching the 'probe' of the switch.
If the coolant level is low it will not turn on the fan.
I don't understand the 'close' reply since IIRC it is just an element stuck in the radiator and the connector for the wire.
Are you by chance talking about the thermostat and not the fan switch?

By closed I mean that electrically the fan switch goes from an open circuit when cool to being closed circuit when hot.

 

[dwalby]

I tested the original fan switch by boiling it on the stove with meter attached. It didn't close. Bought a new one and tested it before installing. It closed a little before boiling. Installed it but the fan still did not come on. Fan works when grounded. Can't understand this. Will test new switch again.

one other possibility is the switch body is not establishing a clean ground. The body of the switch screws into the radiator, so make sure that the area around the threads is clean. Next, my memory is weak on the exact details, but there's a 2-pin connector wire somewhere up in the area where the fan attaches, and that provides the ground connection for the radiator, and therefore the switch. Don't assume the radiator ground is provided by the mounting screws into the frame, that's not the case, so make sure all the wiring from the radiator to that 2-pin connector is corrosion free.

 

[Gman]

one other possibility is the switch body is not establishing a clean ground. The body of the switch screws into the radiator, so make sure that the area around the threads is clean. Next, my memory is weak on the exact details, but there's a 2-pin connector wire somewhere up in the area where the fan attaches, and that provides the ground connection for the radiator, and therefore the switch. Don't assume the radiator ground is provided by the mounting screws into the frame, that's not the case, so make sure all the wiring from the radiator to that 2-pin connector is corrosion free.

Thanks, I had not checked that. I did test from the switch tang to ground and it was not complete when it was hot. I will check that next time I run it.