ST1100 overheating

I recently was on my way back from a cross country trip and one day while in traffic the bike spewed coolant out the overflow. It definitely came out there and not the coolant hoses under the carbs which I replaced last fall. Temp gauge I could also see climbing and I was sure the fan kicked in but could not tell. Anyway I removed some flies and other bugs from the rad with a soft plastic coffee stir stick and chocked it up to not enough air flow. I topped up the coolant bottle with about 500 ml of water while on the road.The rest of the trip was all highway so the bike never got too hot and temp gauge looks like it is sitting in the normal position (s) depending on the weather.

Today I was in traffic again and the same thing happened about 40 minutes from work. Once again I never got a chance to see if the fan came on.

Anyway could it be a thermostat or something else and what is my step? I will do the repairs myself as usual.

Has anyone fitted an extra manual switch for the fan, not that we get a lot of hot weather over here,but on a recent 2up trip,touring slow on almost green lane roads,the ST was getting very hot,I thought if the fan was on constant it might have helped.

A bad radiator cap (won't hold pressure) can also cause overheating problems.

RobbieAG said:

A bad radiator cap (won't hold pressure) can also cause overheating problems.

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Bettin' that is part of issue......if not it WILL be soon if it hasn'rt ever been replaced. That outer rubber seal, if suspicious will have cracks all around its circumferance.

RobbieAG said:

A bad radiator cap (won't hold pressure) can also cause overheating problems.

Click to expand...

Failing finding a split, or leak, at the overflow hose connection point, the rad cap would be the first thing I'd check before digging into the thermostat. The thermostat will only produce overheating if it is stuck closed, or partially closed and it would be a more constant overheat problem.

The 1st inch (okay for you it would be 2.54cm) of the hose going to the overflow as it exits the radiator is probably cracked.

You can clip an inch off and reattach and see if your overflow bottle level goes down after the bike is warmed up and then cools down.
(The overflow will work going to the bottle, with some leakage, but, the reverse flow will not occur due to the cracking fouling up the vacuum.)

Good luck!
Mark

Lots of good info here. I have shortened the overflow hose before but never looked close at the rad cap.

The overflow could have cracked again!

Actually I'm glad you have known of the cracking!

Good luck,
Mark

The overflow could have cracked again!

Actually I'm glad you have known of the cracking!

Good luck,
Mark

The ST puked coolant out the reservoir overflow because it was full. Clearly you have a crack in the hose. Classic symptom. There have been reports of cracks in the hose other than at the thermostat housing nipple. Replace the whole hose with new for peace of mind.

John

Make sure you check the whole length of the overflow hose. Mine had developed cracks midway between the bottle and the radiator. It is simple to replace the whole thing and at 13 years old it is time to do so. Make sure you are refilling the radiator at the cap. Do it while running to get all the air out (start out cold so no steam burns). Then check the fans after the rad is known full.

ak85lp said:

I topped up the coolant bottle with about 500 ml of water while on the road.

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tap water or distilled?

RobbieAG said:

A bad radiator cap (won't hold pressure) can also cause overheating problems.

Click to expand...

Yep, remove cap, turn it over and check if the rubber gasket shows a significant imprint or even cracks...

Overflow hose has been mentioned, but there also other suspicious locations like the O-rings of those dreaded elbows...

Make sure you are refilling the radiator at the cap.

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+1

Your system is low at least the amount that was puked out, plus the amount above the reservoir's "UPPER" level mark.

Got the hose off just now and it was fine except for a slight crack right where it attaches to the small tip on the rad. My hose clamp was behind it though. Stripped it out of the protective sheath and it was fine. Rad cap has no rips or dry pieces. Rad is low in fluid though. Probably should replace both cap and hose for sure.

Cap does have good imprint.

ak85lp said:

Cap does have good imprint.

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Can't remember the part numbers, but several Honda car caps are the same specifications without the cost.
Someone I'm sure will chime in with those stat part numbers.

BTW, not to 'rain on your parade', but once cooling system pressure is back to normal, watch for the vital needed blue/green fluid drips around the alt./centerstand area.........the dreaded coolant elbow/o-ring leaking scenario.

The OP said he did the under-carbs R&R work last fall.

From my cut and paste collection:

Radiator cap Stant 11233/11242
90-96Accord 2.2L 16psi BK7031406
Gates 31336
NAPA 703-2443, 13psi
NAPA 703-1406, 16psi
NAPA BK 7031406
Honda 19045-MY3-621
NAPA 16PSI, #703-1712 (also for the Honda Accord 2.2L) $7.69

John OoSTerhuis said:

The OP said he did the under-carbs R&R work last fall.

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Thanks for the correction John. Sounds like that scoot will be ready for some LD riding.