STILL with the overheating! P250

[wildwildip]

Shop was offering to take another. 002 off the cylinder. I declined. It was not as warped as the head thus I didn't want to take that much off. I also am afraid of changing the compression ratio on the bike, so the less materiel removed the better.  My local kymco tech told me you could get a copper gasket that is + .002 thicker than stock, but you have to custom cust them out, and I dont know the thickness of the OEM head gasket.  As such I ordered a brand new cylinder head gasket and honed about .001 off the cylinder with 600 grit sand paper, just to ensure it was flat. I can go into detail on this process if anyone wants.

So to review,
cylinder head - wrapped by .002 - cylinder head shop took that much off and make it flat again.
cylinder - wrapped by .0015 - i honed .001 or so off it to make it smooth and flat again, really just removed the high spots.
head gasket - replaced with a brand new one.

All coolant is out of the bike, I have also drained all oil.  I will start re assembly tonight and advise on progress and how she does once it start it back up for a test idle.  Be sure to add coolant and oil to bike before you start it up again! Also, I am slightly nervious about the cam timing and cam chain tensioner, I need to be sure to get them installed correctly as to not bend a cylinder head valve.

[jprestonian]

JP you fix your 250S yet?

Mine was a P, not PS.

I sold it for scrap.
.

[wildwildip]

Well thats not good to hear.

update for all - scoot is not put back together yet. I will let you all know how it goes.

Mine was a P, not PS.

I sold it for scrap.
.

[wildwildip]

Well after machining the cylinder and head to flat again the scooter has the same problem again.

The only thing I noticed was hot water getting to the radiator but no warm coolant getting out. Maybe the radiator is clogged or has blockage. Anyone know a way to test radiators for pressure and flow of coolant?

[mrbios]

no chemicals added to the antifreeze instead perform a compression test and report the numbers then perform a leak down test.

the compression test will show how much compression the motor is makingnwhich is a factor of piston rings the valve seated properly a top dead center which involves your timing chain and of course the head gasket.  This is a fairly easy test to perform and when you do the wet test as you can read about online. 

the leakdown test can be done with or without a gauge. basically with the motor at top dead center you put compressed air using an air blower usually with a rubber end that is shaped like a cone you put it up against the Pistons you pressurize it then you listen and look for leaks from three different places:
1. carburetor or throttle body if you have fuel injection - intake valve not seating properly.
2. Exhaust - this indicates a problem with the exhaust valve not sitting properly.
3. air bubbles in the radiator you want to remove the radiator cap- perform this with the engine warm so the thermostat is open so air doesn't get wrapped around the engine block.

[wildwildip]

Well after machining the cylinder and head to flat again the scooter has the same problem again.

The only thing I noticed was hot water getting to the radiator but no warm coolant getting out. Maybe the radiator is clogged or has blockage. Anyone know a way to test radiators for pressure and flow of coolant?

I have removed the radiator and run water though it, it comes out well enough. However I am not sure what I should be compairing it to? I will try my best to flush it, then put it back on and see. I will also remove the thermostat to ensure coolant is getting to the radiator, hopefully doing these two things will stop the overheat message I am getting.

[zombie]

It is usually a vapor lock issue. It's been the same on alot of kymcos.

Easiest way is to remove the TSTAT, and toss it. That will improve the coolant flow enough to expel the air. I just did a 250 2 days ago.

[mrbios]

Anyone know a way to test radiators for pressure and flow of coolant?

.
Two tests for the radiator:
1. pressure test - a small pump like to pump up a basket ball is used to apply pressure.  The system is sealed and the pressure should hold steady but if it begins to drop there is a leak for sure.

2. Flow test: remove radiator and pour water with the garden hose in the top and it should rapidly come out the bottom.  If there is a delay allowing water to build up and overflow then there is a clog. 

[wildwildip]

I removed the thermostat last night and overheat problem is gone. Kymco part# 19300.

I am a bit angry with my shop, as they told me they removed it and tested it, and it was good.  I had a heck of a time removing it, the bolts were on like they never had been removed. I will replace thermostat and see if it keeps on working, but it seriously looks like the thermostat wasn't fully opening after my initial coolant change. Debris must have gotten into the unit after the drain/refill and damaged it.

In short - if you change your coolant and then the bike overheats, pull thermostat first!  Don't listen to the shop technician and rebuild the motor top end like I did!

[mrbios]

I removed the thermostat last night and overheat problem is gone. Kymco part# 19300.
...
In short - if you change your coolant and then the bike overheats, pull thermostat first!  Don't listen to the shop technician and rebuild the motor top end like I did!

For What Its Worth (FWIW)  The Grandvista 250 and certain other brands / models of scooters have super tiny passages where it is extremely difficult to get the air out after a coolant change.  My local dealer confirmed this.  I changed my coolant in the GV250 and ran it with the cap off to let out trapped air until the fan came on twice!  But I still overheated once I drove on the highway!  I then needed to do 3 or 4 more burp sessions to get all the air out.  Since that time everything is back to normal - no over heats in 4K miles.

I don't recommend changing the coolant on the Grandvista for several reasons:

It is harder and takes more work than any car or motorcycle that I have ever owned and you risk damaging your motor or head gasket with an overheat.

You will introduce an air pocket that causes the engine overheat even if you follow the instructions in the book exactly.  This happened to me after I changed the super dark green factory coolant on my 2005 GV250 @10K miles.  I ran the scoot with the radiator cap removed to allow air to escape and reach full operating temperature - twice!  I got on the highway and 8 min later all 5 bars were lit up and blinking on the temp gauge!! Not good!

Coolant is capable of lasting 100K miles and most scooters have much less than 12K  on them.  You might want to change the coolant if it has never been done AND your scoot is 15 years old or more.

Dark Dark Green -  remember, the dark green color does NOT mean the coolant is bad.  It comes that way from the factory so you can see the level in the coolant bottle.

If you insist on changing the coolant:

EZ method - Look up the quantity in the system and remove about 1/2 by pouring it into a container then measure it.  Now fill up with new coolant.  Next year or so repeat.  While you don't change all the coolant or "flush the system"  you DO refresh the chemicals and PH balance.

Correct full method:
As suggested users on this forum and modified by me.... Loosen one bolt from the thermostat and wire brush the threads to remove the factory Loctite - aluminum  threads and a steel fine thread bolt - not a good combination and easy to strip threads! Consider lubing the threads and reinstall.  Repeat for all other bolts.  The reason is to make sure you are able to loosen the thermostat first!  Now drain all coolant.  Now add just enough coolant to insure that the engine block has coolant, reinstall thermostat.  Fill the rest of the way and run the motor with the cap off to allow air to escape. 
Rock & lean the scooter side to side (like throwing over on its side) to get more air out.  My dealers mechanic said this is how they do it!  Run scooter to full operating temp to ensure the thermostat is fully open.

Drive the scooter around the block and keep an eye on the temp!  DO NOT DRIVE ON THE HIGHWAY or a long distance from home.  The coolant is very sneaky the passages are so tiny air gets trapped and once the motor is running at 70%+ it gets hot then overheats!  Expect to have several air expelling / burping sessions with you scooter before ALL air is truly gone. 

[zombie]

Glad to hear you got it Wild. Long road to a short end...

Great post Bios!

[mrbios]

.
Two tests for the radiator:
1. pressure test - a small pump like to pump up a basket ball is used to apply pressure.  The system is sealed and the pressure should hold steady but if it begins to drop there is a leak for sure.

2. Flow test: remove radiator and pour water with the garden hose in the top and it should rapidly come out the bottom.  If there is a delay allowing water to build up and overflow then there is a clog. 

Thanks Zombie.  Now it's my scoots turn to overheat at ~ 21,500 miles.  Only time I had an issue was when I changed the antifreeze.  Today in ~ 87 degree temps on the highway i noticed 3 / 5 bars lit - usually runs at 2 bars unless it is really hot out.  On the way home I noticed 4/5 bars and briefly 5 blinking bars / boxes.  Checked coolant and it was not low, also coolant in the reservoir was only lukewarm.  I think I will remove the TSTAT aka thermostat.  Will update the forum with results.

UPDATE: I removed the thermostat and it took a while to warm up but still overheating.  I rocked the scoot side to side to expel air with radiator cap off.  The radiator does not seem to be very hot.

UPDATE: 07/25/2017 The problem comes and goes.  Around town short rides no problem.  But 8 miles + on the highway sometimes I see 4 bars instead of two.  On the way home same stretch of highway no problem - the normal 2 out of 5 bars.  Could there be a clog in the radiator?  Also, last time it was reading 4 bars I could hear the fan running.

UPDATE: 08/12/2017 Solved? a few days ago I ordered the OEM headgasket on ebay for $15 including shipping (thanks to Sig for suggesting ebay for parts).  Came in a few days.  Installed the headgasket per the manual (wow big job ~ 6 hours total time!) and many things were left out of the manual such as unbolting the engine top mount to push the motor back so the head would clear the metal frame bar the the seat rests on, removing the carburetor studs and tilting the sprocket to get enough slack to get the timing chain off the sprocket and finally how and when to remove the lower chain guide.  I took pictures of the procedure.  I reassembled and to my amazement the motor started right up.  Added coolant but the problem remained.  Today I removed the front plastic and opened up the radiator and it was at least 1/2 empty.  I drained the system flushed with the garden hose and refilled with water and test ran it.  No overheating.  I drained the water and refilled with clean coolant.  Running perfect, for now.  I suspect the head gasket allowed exhaust gas to enter the system and displaced coolant ( I saw coolant from the hole on the bottom of the scooter from the radiator overflow).  Also, the head has signs of coolant leaks around the motor.  However, as is often the case no coolant was in the oil and no oil in the radiator. 

Also, the radiator inside from the little I could see after removing the large side hose was spotless like brand new even after 22K miles.

UPDATE: 09-14-2017 No overheats in about 500 miles.  Mostly runs at 2 out of 5 bars.  The test... Full throttle (I have a throttle lock) for 5 miles on the highway mostly climbing a long grade @80F outside temp.  Mostly stayed at 2/5 bars and hit 3/5 but then fell back to 2/5.  Got off the highway and lots of idling at red lights - 2/5 bars.  I consider the problem resolved.