GT750 Thermostats

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Buffalo-guy
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Post by Buffalo-guy »

I don't think that the thermostat is the problem. For coolant to get out the overflow, it has to get by the rad cap. Have you checked the rad cap, and the filler neck for problems? How full was the system when the problem occurred? A simpler solution may be the one, or not. I had to ask. Cheers.
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Post by Suzukidave »

Something is up for sure Fred as the system should over heat at highway speeds as without the thermostat a portion of the heated coolant is by passing the radiator and going straight back to the pump via the bypass http://www.3cyl.com/mraxl/gt/manuals/gt750man/sr53.htm
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tz375
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Post by tz375 »

Let's think about this for a moment. Wayne told us he swapped out the radiator and thermostat and changed a bypass hose, so it can't be any of those right?

I agree with Fred, that the thermostat is not likely to be the problem, but the fact that removing it fixed things should point to something.

With a closed thermostat the way that the water pumps is up through the barrels and head to the thermostat area and back through the bypass hose to the pump. When the thermostat opens and the bypass closes, water circulates through the radiator.

The implication here is that water is unable to circulate through the bypass system and the pump is pressurizing water in the radiator which cannot get past the thermostat.

What that means, and I realize it makes little sense, is that the bypass is blocked. That blockage could be near the pump or in the thermostat housing. But one way or another, that's what's blocked.
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Post by Suzukidave »

Richard that would explain why it doesnt over heat without the thermostat but is slow to warm up
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Post by Wayne Meuir »

TZ may have it nailed, however, I rebuilt this sucker from the cases up and EVEFYTHING was cleaned out and checked closely before reasembly. The reason I had to tear it down in the first place was that water was getting into the tranny VIA the O-Ring betwen the case halves, so I was damn careful to double check all related items. I put two different NEW Suzuki water pumps on it thinking that the first one might be defective, but it did the same thing with both of them. The bypass hose and all radiator hoses were new as well.
If TZ is correct, what are the risks, other than slow warm up, of leaving the thermostat out? As I said, I have ridden it as much as 300 miles in a day with no hint of overheating or blowing water out the overflow.

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Post by tz375 »

Slow warm up is one issue as is bleed back through the bypass hose instead of via the radiator, but if the bypass hose is blocked, nothing is going that way anyway.

Just take teh time to let it warm up and you should be AOK IMHO
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Re:

Post by GT750Battleship »

tz375 wrote:Don't thermostats always fail to the closed position? There's a spring and bellows causing that.

The GT Thermostat is as bad as any car one. Try to find one that opens early and has a bleed hole or drill a bleed hole in it.

Fit an over temp warning light if you suspect it will be a an issue, but I haven't had too many thermostats failing over the last 40 years. Maybe I got lucky.
Hi,this is now an old thread,but I thought I'd resurrect it :up: I'm about to replace my thermostat for the third time in 14 years & some 73,000 kms & wondering if this is the norm for GT's as far as lifespan goes,or am I a bit unlucky :?: Very hot yesterday 30c + & the temp gauge struggled to get out of the blue zone to the first White line :( I know they "fail open" so will not ride the bike till I replace it....over cooling not quite as bad as the alternative :evil: Radiator is very clean internally,no rust or scale,same goes for the outside,& coolant gets changed regularly.
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Re: GT750 Thermostats

Post by tz375 »

At 30c it seems odd that the temp gauge stayed in the COLD zone. Is it possible that the sender is cactus or there bad connections at the gauge causing it to miss read?

I'd heat the sender and check the voltage/resistance and check the wiring to the gauge and earthing.
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Re: GT750 Thermostats

Post by rngdng »

You've got me thinking about this one again. Really interesting. I vaguely remember a water pump that Suzuki Dave reported that was keyed wrong, and didn't line up with the supply holes in the crankcase. Remember that Dave?? I don't think it was ever run that way, so I can't say that would cause this problem, but I wonder......


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Re: GT750 Thermostats

Post by GT750Battleship »

:up: All good,tested thermostat,it failed the test,slow to open,slow to close,fitted new one yesterday all working as it should,temp gauge now sitting just below the half way mark 8)
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Re: GT750 Thermostats

Post by Suzukidave »

rngdng wrote:You've got me thinking about this one again. Really interesting. I vaguely remember a water pump that Suzuki Dave reported that was keyed wrong, and didn't line up with the supply holes in the crankcase. Remember that Dave?? I don't think it was ever run that way, so I can't say that would cause this problem, but I wonder......


Lane
Way late responding but your right Lane , there were replacement pumps sold that were keyed wrong so the hole in the side of the pump didnt line up with the passage in the case .
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Re: GT750 Thermostats

Post by simmons1 »

I own Wayne's old bike and it still runs great despite not having a thermostat. It takes a while to warm up but never overheats even on 100+ degree days on the highway.

I have not done any trouble shooting as I haven't had any issues.
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Re: GT750 Thermostats

Post by tz375 »

Does it still have that cool looking TCE 3 into 1 exhaust?
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Re: GT750 Thermostats

Post by simmons1 »

tz375 wrote:Does it still have that cool looking TCE 3 into 1 exhaust?
For now. I have a set of Higgspeeds on order. The TCE may be for sale some day.
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Re: GT750 Thermostats

Post by Suzukidave »

For sure something isnt right as it shouldnt be running at the correct temp without a thermostat .
the older i get the faster i was
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