Low coolant temperature on GT200
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Enthusiast
Vespa GT 200 L
Joined: 09 Jan 2015
Posts: 63
Location: Lviv, Ukraine
Sat May 11, 2019 2:42 am quote
Hello gentlemen
Before servicing, arrow of the gauge was always in the middle while riding.
I did a valve adjustment (intake was overtightened - now it's 0.10mm, exhaust was 0.20mm instead of 0.15mm).
Also, I have replaced a leaking thermostat and its cover.

Now, arrow always looks like this, is it a good temperature?
I did 20km in "full throttle" mode, after that I was able to see it pointing to the middle after few minutes of idling.

Thank You very much for help and participation!

P90510-212303.jpg

Lurker
2006 GT200L
Joined: 11 May 2019
Posts: 1
Location: North Port FL
Sat May 11, 2019 5:20 am quote
I've wondered about that, too. My 06 GT200 with 10k miles always reads low.
Enthusiast
Vespa GT 200 L
Joined: 09 Jan 2015
Posts: 63
Location: Lviv, Ukraine
Sat May 11, 2019 6:00 am quote
Well, at least we are not lonely now)
Moderaptor
The Hornet (GT200, aka Love Bug) and 'Dimples' - a GTS 300
Joined: 26 Aug 2007
Posts: 37222
Location: Pleasant Hill, CA
Sat May 11, 2019 7:31 am quote
Mine does that too. Not fussed by it.
Addicted
Joined: 29 Apr 2018
Posts: 665

Sat May 11, 2019 8:58 am quote
Too high wouldbe bad, but too low can cause problems also. I think one of the early 500 cc aprilia scooters had the wrong thermostats znd it somehow caused engine lroblems because the motor never warmed up properly or it could be this old fart is having a brain lapse.
Molto Verboso
Gina, 1965 Vespa 180SS, Bella,1968 Vespa 150 Super, (Both NZ new Airco assembled), Francesca, 2006 Vespa LX150, Sofia, 2007 Vespa GT200
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Location: Hamilton, NZ
Sat May 11, 2019 7:01 pm quote
Mine has run low occasionally and in particular on a longer run low load generally downhill section. I talked to the local dealer and he was unconcerned. Like most, he said high temperatures are a bigger problem, particularly if the fan doesn't kick in. I know that bit works okay and the scooter runs really well so I relax and enjoy the ride.
Molto Verboso
2016 Vespa GTS300ie abs/asr/ess Settantesimo '70'
Joined: 11 Jun 2011
Posts: 1910
Location: Not really sure but I think somewhere down South, in the engineering dept at Starfleet's UK HQ
Sun May 12, 2019 2:27 am quote
Did you get all the air out of your cooling sytem. If not that can give a lower temperature reading. Most air finds it's way to the thermostat housing where it can interfere with the function of the thermostat. Often this can cause it to stick partially open causing the engine to run cooler. Not good! Try re-bleeding the air from your system. You may find that suddenly it reads correctly again. If you run it for a long period with air in the system it can cause the thermostat to stick partially open, permanently.
Addicted
2007 GT200, 2008 Yamaha C3
Joined: 27 Jul 2012
Posts: 521
Location: Denver
Sun May 12, 2019 3:26 am quote
GT200 has a self bleeding system. Air in there wouldn't cause it to run cool anyway. Could be running cooler now that the valves are adjusted correctly. Mine never made it above 3/8 even in the dead of summer.
Molto Verboso
2016 Vespa GTS300ie abs/asr/ess Settantesimo '70'
Joined: 11 Jun 2011
Posts: 1910
Location: Not really sure but I think somewhere down South, in the engineering dept at Starfleet's UK HQ
Sun May 12, 2019 11:48 pm quote
The self bleed system doesn't work very well on the GT's. In the workshop we are wary of them. That's why they don't use the self bleed on the GTS's. If air is in the thermostat housing it can cause the stat to run partially dry leading to the stat not closing properly because of the build up of deposits on the slider. If it doesn't close properly this means the motor never or rarely reaches full normal working temperature. Stats regulate the engine temperature even when the motor is hot, and if it's defective you can find your motor running cooler than it should. I've had to replace the stat on a GT and GTS due to this very thing. Of course, it may not be that for the op but I'm suspicious due to the fact the temp guage was working just fine before he replaced the stat housing & gasket. So, assuming it's the right stat, the next thing is checking for air. It's what we would do in the workshop. If that's ok we would check the connections are clean to the temp sender unit and measure the resistance. Just saying it's something to check.

The engine valves were not out of adjustment anywhere near enough to make a difference to engine temp before or after adjustment. Valves have to be out of adjustment very significantly for that to happen. Notice also the op says it was only the INTAKE valves that were tight. This would not make a difference to engine temp anyway, but if out by alot the engine would have been running very erratically indeed.
Enthusiast
Vespa GT 200 L
Joined: 09 Jan 2015
Posts: 63
Location: Lviv, Ukraine
Mon May 13, 2019 1:02 am quote
Stromrider wrote:
Did you get all the air out of your cooling sytem. If not that can give a lower temperature reading. Most air finds it's way to the thermostat housing where it can interfere with the function of the thermostat. Often this can cause it to stick partially open causing the engine to run cooler. Not good! Try re-bleeding the air from your system. You may find that suddenly it reads correctly again. If you run it for a long period with air in the system it can cause the thermostat to stick partially open, permanently.
GT200 doesn't have a bleeder screw on the cover, what would be the best method to bleed the system there?
The only idea I get, is to loosen thermostat cover or disconnect the hose to carburetor.

Thank You!
Molto Verboso
2016 Vespa GTS300ie abs/asr/ess Settantesimo '70'
Joined: 11 Jun 2011
Posts: 1910
Location: Not really sure but I think somewhere down South, in the engineering dept at Starfleet's UK HQ
Mon May 13, 2019 1:40 am quote
The hose near the carb is the only way if it doesn't self bleed. About one in 5 GT's don't seem to bleed themselves fully.
Enthusiast
Vespa GT 200 L
Joined: 09 Jan 2015
Posts: 63
Location: Lviv, Ukraine
Tue Jun 18, 2019 1:15 pm quote
Thank You very much for help.
I've disconnected the hose two times to release the air and few days later I have noticed that temperature is in the middle of the gauge in city traffic - seems to be nice.
Even more, on Vespa World Days, in a traffic jam of vespas, waiting for parade - even cooler started to work!
Molto Verboso
2016 Vespa GTS300ie abs/asr/ess Settantesimo '70'
Joined: 11 Jun 2011
Posts: 1910
Location: Not really sure but I think somewhere down South, in the engineering dept at Starfleet's UK HQ
Wed Jun 19, 2019 12:56 am quote
Well done Kyka. It's nearly always air in the thermostat housing that causes symptoms such as yours. Thanks for posting back about it, it's helpful to everyone to have confirmation of an issue and it's fix. Thank you.
Addicted
2006 LX150 (carbed) | 2007 GT200
Joined: 29 Jun 2016
Posts: 659
Location: Toronto
Wed Jun 19, 2019 1:26 am quote
To bleed at the thermostat housing, do you disconnect the hose to the carb (6"), or the little elbow hose (2")? Does it matter when you bleed - should the bike be cold, hot, or it doesn't matter?
Enthusiast
Vespa GT 200 L
Joined: 09 Jan 2015
Posts: 63
Location: Lviv, Ukraine
Wed Jun 19, 2019 3:09 am quote
Stromrider wrote:
Well done Kyka. It's nearly always air in the thermostat housing that causes symptoms such as yours. Thanks for posting back about it, it's helpful to everyone to have confirmation of an issue and it's fix. Thank you.
Thank You for finding time to help!
berto wrote:
To bleed at the thermostat housing, do you disconnect the hose to the carb (6"), or the little elbow hose (2")? Does it matter when you bleed - should the bike be cold, hot, or it doesn't matter?
I've did it on a cold first and then warmed it a little and did it one more time.
But be aware, if engine will be too warm or hot - You may be injured by a hot coolant under the pressure coming out of tube.

Here is that tube (a longer one)

P90619-133814.jpg

Addicted
2006 LX150 (carbed) | 2007 GT200
Joined: 29 Jun 2016
Posts: 659
Location: Toronto
Wed Jun 19, 2019 7:11 am quote
Thanks for the very helpful reply!

When you opened that line, I guess you saw some "bubbly" liquid (coolant and air) coming out for a few seconds, and then it became more consistent liquid only (at which point you replace the hose)?
Enthusiast
Vespa GT 200 L
Joined: 09 Jan 2015
Posts: 63
Location: Lviv, Ukraine
Wed Jun 19, 2019 8:27 am quote
berto wrote:
Thanks for the very helpful reply!

When you opened that line, I guess you saw some "bubbly" liquid (coolant and air) coming out for a few seconds, and then it became more consistent liquid only (at which point you replace the hose)?
I expected to see bubbles, but coolant was coming out right away so fast, so I'm not sure what I saw)
Addicted
two Vespa GTSs (Dragon Red and Black). GT 200 - Kymco Yager 200i
Joined: 19 Oct 2009
Posts: 539
Location: Saratoga Springs, New York
Wed Jun 19, 2019 9:04 am quote
Wow, glad to see this and the timing couldn’t be better. I bought a low mileage GT last summer as a second scooter for my wife and only noticed this Spring that the gauge read one-quarter after being fully warmed up, exactly like the original poster. If left to idle, it will rise to the appropriate level and the fan comes on. The two GTSs I own both stay at one-half when fully warmed.
I decided not to worry about it, but I assumed the thermostat was opening too early.
Molto Verboso
2016 Vespa GTS300ie abs/asr/ess Settantesimo '70'
Joined: 11 Jun 2011
Posts: 1910
Location: Not really sure but I think somewhere down South, in the engineering dept at Starfleet's UK HQ
Thu Jun 20, 2019 12:56 am quote
Yes on the GT, many don't always self bleed correctly and you end up running around with a small amount of air in the system. This causes the thermostat to stick open just a little. The thermostat fails to close properly causing the engine to run cooler than it should. It hardly ever reaches normal operating temperature. This isn't good for the engine as the thermostat fails to fully regulate the engine operating temperature when it's hot or cold. Looking at the design of the stat and housing you'd think it would always self bleed, but for some reason it doesn't always go that way. Anyone who has the issue of the gauge not reading 'normal' engine temp when hot should consider checking for air. Of course, there can be other causes too, but the air is the most common one you come across.
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