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 Post subject: Re: GT750 Thermostats
PostPosted: Sun Apr 16, 2017 4:00 pm 
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tz375 wrote:
If it's blowing out of the overflow when it's hot and running hard, it's possible that you won't smell it, but you could try routing the overflow hose into a plastic bottle and see if it collects anything.


Suzukidave wrote:
Talking about torquing , have you tried giving the head bolts a torque test before you remove it just to see if that could be the problem ?


I had a couple hours to mess with the bike after Easter dinner.


1. I checked the torque on the head bolts. The torque was good on all of the bolts.

2. I removed the radiator cap and took it to the Autozone around the corner to test. Spec says 13psi. It leaked at 11ish. Bought a new cap for a 78 F150. Tested it in the store at 13 and change. They also let you borrow the tool to test the cooling system.

3. Back around the corner to the house. I pull the spark plugs and pressurize the system to 20psi for about 15 minutes. The plugs look great color wise. The gauge doesn't leak down at all. I am cooking with gas now so I return the pressure tester.

4. I refill the radiator to the bottom tang and button things up with the new cap, except for putting the overflow house in a plastic bottle on the side of the bike.

5. I start the bike and a tiny bit of coolant immediately winds up in the bottle. I am thinking it was left over in the line so I dump it out and let the bike idle for a couple more minutes.

6. Time for a test ride. I take street out of the neighborhood and wait for the red light. Bottle still looks empty. I run it through the gears and at the next light look down and see antifreeze in the bottle so I head for home. Total ride was roughly 3 miles.

When I got home I took one picture and a quick video. I am thinking that even though it pressure tested good at 20 psi and has a new cap, the head gasket is leaking based on the air bubbles in the antifreeze in the bottle.

Image

This should be a video if you click on it.

Image

Is it time to remove the head?

Thanks for all of your help so far.

Rich

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 Post subject: Re: GT750 Thermostats
PostPosted: Sun Apr 16, 2017 8:02 pm 
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Absolutely. Off with its head.

But before you do that, check one more thing. It is possible that the top of the radiator is not smooth and flat and maybe allowing pressure to pass. The stock arrangement of filler neck and bypass hose and header tank is all a bit of a PIA.

You may have to pop the fuel tank off to do this, but try to put a clamp around the overflow hose at the filler neck and then find a way to add some pressure to the overflow hose in reverse direction and see if it bubbles and leaks at the filler cap. What you are trying to test is how well the cap seals onto that neck. If that doesn't reveal a poor seal, have it's head off and fit a new head gasket.


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 Post subject: Re: GT750 Thermostats
PostPosted: Sun Apr 16, 2017 8:18 pm 
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tz375 wrote:
Absolutely. Off with its head.

But before you do that, check one more thing. It is possible that the top of the radiator is not smooth and flat and maybe allowing pressure to pass. The stock arrangement of filler neck and bypass hose and header tank is all a bit of a PIA.

You may have to pop the fuel tank off to do this, but try to put a clamp around the overflow hose at the filler neck and then find a way to add some pressure to the overflow hose in reverse direction and see if it bubbles and leaks at the filler cap. What you are trying to test is how well the cap seals onto that neck. If that doesn't reveal a poor seal, have it's head off and fit a new head gasket.


I'll try it, but wouldn't the pressure tester I used from Auto zone leaked? It held 20 psi without leaking a psi for 15 minutes.

Forgot to ask where is the air coming fro making the bubbles?

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 Post subject: Re: GT750 Thermostats
PostPosted: Sun Apr 16, 2017 10:04 pm 
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I would expect to, but it depends on how it sealed in the filler neck.

I have a GT that had a slight accident over the winter and it has a TR750 type radiator, so no neck extension etc. I just took the tank off and fitted a shortened tire valve into the overflow tube. Then I attached a simple tire pump and pumped it up to 15psi. I could hear hissing and it turned out to be the filler cap not sealing. No worries, I had three or 4 more...... and they all leaked. Some a little and some a lot.

So I took the cap off another bike that I know is good and that held 15psi for more than 10 minutes. No apparent leak into the motor in my case. When I fill it with water and warm it up, I'll repeat that to be sure.

I had expected to need a squirt mister bottle of soapy water to find the leak, but it wasn't necessary in my case. The idea is to spray a mist of water with a little dish soap in it where you suspect it might be leaking and watch for bubbles. In my case, not necessary because the air leak was easy to find.


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 Post subject: Re: GT750 Thermostats
PostPosted: Mon Apr 17, 2017 5:08 am 
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Location: Lancaster Pa.
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Bikes owned: GT750 x2 97 -1200 Bandit 86 GSXR1100
And while the head is off you maybe should put a thermostat back in .

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 Post subject: Re: GT750 Thermostats
PostPosted: Mon Apr 17, 2017 5:46 am 
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tz375 wrote:
I would expect to, but it depends on how it sealed in the filler neck.

I have a GT that had a slight accident over the winter and it has a TR750 type radiator, so no neck extension etc. I just took the tank off and fitted a shortened tire valve into the overflow tube. Then I attached a simple tire pump and pumped it up to 15psi. I could hear hissing and it turned out to be the filler cap not sealing. No worries, I had three or 4 more...... and they all leaked. Some a little and some a lot.

So I took the cap off another bike that I know is good and that held 15psi for more than 10 minutes. No apparent leak into the motor in my case. When I fill it with water and warm it up, I'll repeat that to be sure.

I had expected to need a squirt mister bottle of soapy water to find the leak, but it wasn't necessary in my case. The idea is to spray a mist of water with a little dish soap in it where you suspect it might be leaking and watch for bubbles. In my case, not necessary because the air leak was easy to find.



What is the fix if it leaks here? Try caps until I get one that seals?

Thanks!

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 Post subject: Re: GT750 Thermostats
PostPosted: Mon Apr 17, 2017 5:50 am 
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Suzukidave wrote:
And while the head is off you maybe should put a thermostat back in .


That is what I plan on doing. A bunch of posts back Wayne did mention that the bike didn't consume/blowby coolant. I have had to add coolant as long as I have owned the bike. I am hoping that when this gets figured out I can use a thermostat.

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 Post subject: Re: GT750 Thermostats
PostPosted: Mon Apr 17, 2017 1:22 pm 
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simmons1 wrote:
tz375 wrote:
I would expect to, but it depends on how it sealed in the filler neck.

What is the fix if it leaks here? Try caps until I get one that seals?

Thanks!


I would just buy a new cap and see if that seals. If the filler neck is damaged, that may have to be replaced, but more likely to be old hard rubber seal no longer doing what it's supposed to do.

BTW, the valve stem I used was a bolt in type from a GS cast wheel that I cut the bottom off so it was really just a long tube with a valve inside. And teh only reason that pressure finally dropped was a weep in the valve. 40 year old parts don't work like they used to... :? :lol:


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 Post subject: Re: GT750 Thermostats
PostPosted: Mon Apr 17, 2017 8:19 pm 
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tz375 wrote:
simmons1 wrote:
tz375 wrote:
I would expect to, but it depends on how it sealed in the filler neck.

What is the fix if it leaks here? Try caps until I get one that seals?

Thanks!


I would just buy a new cap and see if that seals. If the filler neck is damaged, that may have to be replaced, but more likely to be old hard rubber seal no longer doing what it's supposed to do.

BTW, the valve stem I used was a bolt in type from a GS cast wheel that I cut the bottom off so it was really just a long tube with a valve inside. And teh only reason that pressure finally dropped was a weep in the valve. 40 year old parts don't work like they used to... :? :lol:


The test done in my picture and video was with a brand new cap.

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 Post subject: Re: GT750 Thermostats
PostPosted: Tue Apr 18, 2017 12:32 am 
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Oh dear - or words to that general emotional intent... aka Far Kinhill

The seating surface may be damaged and not allowing it to seal. Get a schrader valve stem and push it into the overflow hose and use a tire pump to add 10-20 pounds of air pressure and listen for leaks. If it leaks around the cap, you need a new filler neck.

If you cannot hear leaks but the pressure is dropping, it is an internal leak ie the head gasket.


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 Post subject: Re: GT750 Thermostats
PostPosted: Tue Apr 18, 2017 4:43 am 
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tz375 wrote:
Oh dear - or words to that general emotional intent... aka Far Kinhill

The seating surface may be damaged and not allowing it to seal. Get a schrader valve stem and push it into the overflow hose and use a tire pump to add 10-20 pounds of air pressure and listen for leaks. If it leaks around the cap, you need a new filler neck.

If you cannot hear leaks but the pressure is dropping, it is an internal leak ie the head gasket.


Still confused, I pressurized the system to 20 lbs with the tester I borrowed from the autoparts store. It held 20 pounds for 15 minutes. The only difference between it and the new cap is that the tester
has a stiffer spring designed to hold 30 pounds.

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 Post subject: Re: GT750 Thermostats
PostPosted: Tue Apr 18, 2017 8:18 am 
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This is where long distance is a problem. You are saying that the tester sealed therefore a cap should also seal. That seems perfectly logical.

I cannot see what that tester looks like and I am speculating that the tester with higher clamping pressure and probably more effective seal may be sealing better than a stock cap and masking the issue. That's why I suggested a simple cheap way to test that theory.

From the write up on that run, it may be that the head/cap is only leaking measurably when it gets hot. If you slip a schrader valve stem into the overflow pipe, it would be easy to test cold and hot and not have to go anywhere near the hot parts to do so.


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 Post subject: Re: GT750 Thermostats
PostPosted: Tue Apr 18, 2017 9:25 am 
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When you tested the system to hold pressure was the engine hot or cold .. maybe that would make the difference if the engine is hot ?

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 Post subject: Re: GT750 Thermostats
PostPosted: Tue Apr 18, 2017 7:04 pm 
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Suzukidave wrote:
When you tested the system to hold pressure was the engine hot or cold .. maybe that would make the difference if the engine is hot ?



The new and old cap and system was pressure checked cold.

Going Dualsport in NWA for a few days it may be week before I get to mess with the some more.

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 Post subject: Re: GT750 Thermostats
PostPosted: Wed May 31, 2017 9:32 am 
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Country: Netherlands
Bikes owned: GT750 GSX750ES
I'm a bit of a lurker but this thread has so many similarities to my GT750 I had to respond!

Last weekend it started overheating, the thermostat seems to open and close properly when boiled but I had to remove it to prevent it from overheating. Thing is, it kept cool (first mark above the blue C area) the entire day of riding, at 30 degrees C and most of the time riding it hard in the mountains. Without closing the bypass hose I might add. The engine has been fully rebuild couple of thousand km's ago with new seals, gaskets, O-rings etc. Seems to me the cooling system is more than adequate to work without thermostat?


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