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GT200L
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Hello ModernVespa hivemind,

Last night coming home I noticed that the temp gauge on my GT200L was all the way up to the edge of the red zone. I pulled over and was surprised since I had done a coolant flush and change this spring I had never seen it get over the 1/4 mark. I also noted that I had coolant on the floorboard.

I shut it down and arranged for a pickup. Now I have the glovebox taken off so I can see the radiators as well as the fan. It looks like the coolant was leaking from the expansion tank cap, no sign of leaks at the radiator or any of the hoses.

I started up the scooter and after about 5-10 minutes the temp gauge was back up near the red, the radiators were only lukewarm and still the fan did not turn on. I used the coolant recommended by the local Vespa dealer and regular checks suggest that I did not have a coolant leak. I do not see any evidence of coolant leaking from the weep hole and the oil still looks like new.

I have a thermostat as well as coolant on order, does this sound like a stuck thermostat, or am I looking at a new waterpump, or is there something else I am missing?

Thanks for the help.
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If the bike gets hot and forces coolant out of the radiator cap, there's a chance the head gasket is blown. Exhaust gets forced into the water channels and pushes coolant up out of the system. That explains why you aren't feeling a lot of heat on the radiators.
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And if the radiators aren't getting hot, the fan won't kick in, as the fan switch is a thermal switch in the LH radiator feed.

Head gasket time. Not the worst job to do on a GT by a long chalk!
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GT200L
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Thank you for your insight. Bummer, that seems to make sense, I typically ride around town 40 MPH or less and last night I rode about 100 miles on the freeway at 70+. Scooter only has 7000 miles so I was hoping I wouldn't have major issues for at least a couple of years. Anything I can do to confirm that the head gasket is the issue?
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There's nothing much else it could be, sorry. The parts are cheap, there are several Youtube videos showing the procedure, and the workshop manual covers it pretty well.

https://manuals.wotmeworry.org.uk/Vespa/GT125%20GT200%20Euro2/
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GT200L
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Understood,

I spent about 15 minutes looking for a procedure or video, nothing found yet. If you have a link and wouldn't mind posting it, I would very much appreciate it.

At a minimum,, I am assuming that the engine needs to come out though and that seems to be pretty well documented in the manual you posted the link to, appreciate you posting that link.
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Check the circuit board inside the clock housing. Mine did the same and it wasn't the engine over heating.

The clocks were duff.
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Bill Dog wrote:
Check the circuit board inside the clock housing. Mine did the same and it wasn't the engine over heating.

The clocks were duff.
That may be so, but you didn't have coolant spewing out of the filler cap did you! The clocks are fuck-all to do with this case.
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Yup. Mine oddly enough stayed in tact which must have been a first.

I think you brought it soon after.
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Thanks BillDog for the suggestion, I wish it was a gauge problem so I could ignore it. Unfortunately with the leaking coolant that definitely suggests there is another problem.

I did pull the thermostat last night and inspected the water pump, both appear to be intact and functional, so I agree with Jimc's assessment. Still on the hunt for some kind of tutorial before tackling this though.
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You'll have to forgive me as I skimmed through your post without reading much of the detail.

It's one of my many faults.

I wish you the best of luck with the repair.
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The workshop manual covers it, you have to remove the engine first, pages 90-95, then page 127 onward for the cylinder head:
https://manuals.wotmeworry.org.uk/Vespa/GT125%20GT200%20Euro2/
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There must be coolant in the engine oil, you risk damaging the connecting rod bearing.
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Attila wrote:
There must be coolant in the engine oil, you risk damaging the connecting rod bearing.
Not 'must' - there *might* be coolant in the oil, but I doubt it. A head gasket split that spews coolant is usually just the combustion chamber direct to a coolant channel.
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Thanks Jimc for providing page numbers. That is helpful.

I did inspect the engine oil as well as the coolant, it does not look like either have been contaminated. That being said, I have already drained the coolant to inspect the thermostat and if I am pulling the engine, while it is out, I will change the oil, oil filter, adjust valves replace sparkplug etc.

I am hoping that riding with the temp gauge almost in the red for awhile before I noticed it didn't warp the head. It did die at the first traffic light when I got off of the freeway, but restarted fine.
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Before you dive into head gasket worries, try it with no thermostat, as it could cause the issues. If it still does it after that head gasket is likely. If you want to be 100% sure then you can buy a liquid test kit for about £10 that tests the coolant for combustion gases.
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GT200L
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Thanks for the suggestion, too late though, I have already worked through all but the last two steps in the service manual to pull the motor, so I am pretty committed to replacing the headgasket at this point. I'll replace the spark plug and do valves while I have the engine out as well.
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GT200L
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GT200L
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Greetings Modern Vespa hivemind. I have been able to pull the engine, have the belt and valve cover off in the process of replacing the head gasket, but am unsure what to do next. The manual is confusing. I would appreciate any insights regarding next steps in removing the head.
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OP
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Enthusiast
GT200L
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GT200L
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Over on ADV rider a nice person shared this video it really helped fill in the gaps in the service manual for me. Thought I would post the link here in case someone else in the future is looking for it.

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GT200L
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GT200L
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After watching that video, I was able to get the head off and am looking at the head cover gasket. I don't see an obvious sign of failure except all of the black stuff coming off of the gasket. Wondering if that was some kind of a sealant... Unfortunately after a 3 hour round trip to the Vespa dealership for a head gasket, they actually gave me a valve cover gasket. Bummer, should have checked more closely. Have to wait until Tuesday when they open again and then will have to wait until it arrives in the mail. Thanks everyone so far for the help!
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Enthusiast
GT200L
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GT200L
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Found the root cause of the problem. Looks like the water pump bearings seized and the plastic part that drives the water pump melted. Odd at only 7000 miles. Probably should have pulled this apart first before pulling the engine and head gasket, but that is okay. I am learning and finding the work interesting. Thanks everyone for the help so far! Appreciate the supportive community.
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Molto Verboso
2022 Liberty 150S-"Meg"-SOLD
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Molto Verboso
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Make sure to check the stud o-rings before you put on the new head gasket. If they're damaged, you'll get coolant seepage. Robot mentions them in one of his rebuild videos.
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GT200L
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GT200L
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Replaced water pump and head gasket, just got back from a quick 25 mile ride and everything seems good. Thanks everyone for the help and support!
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