Bizarre T-STAT activity

T-STat on the 94' was stuck open. Replaced with new one. First day it seemed to be running hot. Next day I took it to work and the temp gauge kept creeping up and up, very slowly. Returned from work today, same thing. I did not temp check new stat out of the box, I think Its probably stuck slightly open?

hotrod1 said:

T-STat on the 94' was stuck open. Replaced with new one. First day it seemed to be running hot. Next day I took it to work and the temp gauge kept creeping up and up, very slowly. Returned from work today, same thing. I did not temp check new stat out of the box, I think Its probably stuck slightly open?

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Did you replace the cap also? The outer rubber seal on inside of cap gets cracks/splits around its circumferance. A guarentee it won't seal properly.....BTDT.

Brant said:

Did you replace the cap also? The outer rubber seal on inside of cap gets cracks/splits around its circumferance. A guarentee it won't seal properly.....BTDT.

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oopppss.....see you kinda jumped threads, where I saw you replaced the cap.
With that, I'd check the easiest.......pull some tupperware off while its cold and check coolant level IN radiator. Radiator HAS to be full....to the VERY top, aside where the level is in the overflow tank.

Brant said:

oopppss.....see you kinda jumped threads, where I saw you replaced the cap.
With that, I'd check the easiest.......pull some tupperware off while its cold and check coolant level IN radiator. Radiator HAS to be full....to the VERY top, aside where the level is in the overflow tank.

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I'm with Brant...first thing I'd do is check the coolant level at the radiator, then check the hose from the filler neck to the overflow bottle.

Thanks Brant an Gymbo, pulling it tomorrow, testing and replace with new. I have never had this happen before with a new thermostat. I did replace cap and its full of fresh fluid.

hotrod1 said:

...First day it seemed to be running hot. Next day I took it to work and the temp gauge kept creeping up and up, very slowly...

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At what speeds and ambient temps were you moving?

I'd first check for low coolant levels (exposing the temp probe, thus high readings) and anything causing such...

Another issue would be reduced coolant flow, pump impeller and such, but lets not go there yet...

Coolant levels good, 110-114 f. It gradually increases to almost overheat. I'm pretty sure it's a bad (new) stat...Let you know later...

hotrod1 said:

I'm pretty sure it's a bad (new) stat...Let you know later...

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I'm not convinced on that...
Did the fan kick in or not??
Still possible that the fan-stat is faulty/providing poor contact... or the motor itself is dodgy... (had seen some with the shaft spinning freely in the prop...)

The fan did kick on at the right time, every time, getting ready to dig into it right now. Prior to all this, before changing out the stat, it ran cold with an stuck open stat. Thats why I think it's a bad stat out of the box...I will let you know..Rod

Is it possible to install the thermostat upside down ? I know a guy who installed a new thermostat in his Jeep upside down and the temp gauge was acting like yours is now. Just a thought. I believe on the ST1100, the "spring" side goes in first. Usually, the stat will only install one way, but on his Jeep, it would fit either way.

Fuel sending unit, Interesting! My fuel gauge stopped working when I repaired the tank on the 94'. I just took the bike apart, stat works well in hot water, However, comparing old and new, the old one has a much larger opening compared to the new Stant stat. STrying to get ready for a ride in 2 days. I removed the the stat, removed the jingle valve and drilled a couple of holes for flow. I also cut a little of the hoses due to hardness/cracking. I thought about just assembling without the stat because it's so hot in Vegas now. I did all this to the 93' and the 94'. I'll take them for a ride tonight for a test. Thanks all....Rod

hotrod1 said:

Fuel sending unit, Interesting! My fuel gauge stopped working when I repaired the tank on the 94'. I just took the bike apart, stat works well in hot water, However, comparing old and new, the old one has a much larger opening compared to the new Stant stat. STrying to get ready for a ride in 2 days. I removed the the stat, removed the jingle valve and drilled a couple of holes for flow. I also cut a little of the hoses due to hardness/cracking. I thought about just assembling without the stat because it's so hot in Vegas now. I did all this to the 93' and the 94'. I'll take them for a ride tonight for a test. Thanks all....Rod

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Good in thought only...... a properly working thermostat KEEPS it from getting too hot.....and from getting too cold.
Plus, engine at a more constant temperature performs better, gets better mileage....and is just all-round more 'happy'..

Wrapped it up for the day. I'm going to run the 94' without a stat on the trip, should not be a problem in 115 f. temps, and over 120 in Death Valley. 93', new stat with a couple of holes drilled to increase flow. I will have to replace them later with an OE stat or an aftermarket with a larger opening surface. New coolant and refreshed hoses should make cooling a little better. Also synched the carbs, flushed fluids.

Oh, the thermostats were installed in the right direction.

Thanks all.......Rod

Have a safe ride! Report back your findings.

hotrod1 said:

...drilled a couple of holes for flow...

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Normally not needed... the one bore is enough as small bypass till the coolant has warmed up...

Was there brownish stained coolant inside the system when you got the bike?... (I guess we know where I'm heading there...)

Both bikes performed well. The one with the coolant question still seemed to run hooter than normal, with no t-stat installed. It never hit the far right line of the temperature scale, but it was close to 3/4 or 7/8. Only problem on this 1100 mile trip was the vacuum fuel valve shut down the bike, after bypassing it ran strong again.

hotrod1 said:

The one with the coolant question still seemed to run hooter than normal, with no t-stat installed.

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Radiator fins clogged or, hate to ask, has the w/pump ever been replaced?

I do not know about the water pump, but now I am starting to believe it to be suspect. I drove it home from work today, and the temp keeps rising, ever so gradually until its one needle width away from the far right black line. Fan does kick on, but it should not be so warm even in 110f temps on the freeway, any more input/advise is appreciated!

You mentioned that it ran cold with the old stat. So that tells me that something happened during the stat change. a) Either the replacement stat is bad (if I understand correctly you eliminated that problem by taking it out) although I personally have never seen a new stat be bad. or, much more likely: b) something else went wrong during the initial stat-change. Is there a hose got pinched or collapsed? Sometimes the inner layer of a hose will separate and cause an obstruction which could have happened during the initial stat-change what with twisting and moving the hoses in a way that they weren't used to being moved. Or a piece of crud got dislodged and is causing an obstruction somewhere. Is there a place where the ST1100's can get an airlock? Do they have a bleeder valve somewhere that needs to be bled? (I'm not familiar with the cooling system on an ST1100.) If you get to the point where its easy to remove the radiator, try doing a flow test on it. You should be able to put a garden hose in one end and have it freely flow thro the other end.

Thanks Art. I drove it to work again in the wee am hours when cool, 90f. Still getting too hot, but not all the way right. I'm planning on starting over when I get home tomorrow. On another thread some others have found that a loose negative ground might be the problem. So I will check that too, one thing I failed to mention when I first did all this, I flushed the system with a flush for about 10 minutes. Replaced with new t-stat and cap and fluid.

ST1100Y, Will check and clean the radiator itself, what is your implication regarding a new water pump?..I'm pretty sure it's the original Thank all........Rod