STILL with the overheating! P250

[wildwildip]

It's been in the shop over six weeks, and I won't tell you what caused this issue. All I can say is that I got the repairs at-cost, and that was a whole lot less than I would have otherwise paid. I have an awesome dealer, and I can't say that enough!

I know this is an old thread, but my P250 has a similar issue and I would love to know what fixed the problem with this scoot.

[wildwildip]

Well my 09 P250S has been in the shop for a month and they cant figure out the issue with the over heating.

It has a new thermostat and the thermo sensor works fine.  No leaks, radiator holds pressure.

They filled it up again and it keeps over heating, even though it is pumping coolant.  Anyone have any thoughts? I am shocked the dealer couldn't find the issue.

[jprestonian]

Your cylinder head is warped. Have it machined/milled flat, put it back together with a new set of gaskets. DO NOT OVER-TORQUE THE HEAD when reassembling!
.

[wildwildip]

Is that what happened to yours?

Anyway I can tell if that's the case before I disassemble?

[wildwildip]

Also, is it the head that needs to me milled or the head and cylinder as well?

Does this change the compression or stroke clearances after milling? Maybe I should install two head gaskets to keep the spacing correct...

[jprestonian]

Is that what happened to yours?

Anyway I can tell if that's the case before I disassemble?

1.) That's the working theory, at least;
2.) You can test the radiator contents for exhaust fumes. There are kits that contain a chemical that will change color to indicate the presence of exhaust gases in the cooling system -- I do not have any first-hand experience with this, but several mechanics have described this to me.

3.) (in answer to compression, stroke, etc. in other post) -- Good questions. I'm guessing buying replacement head & cylinder is the only way to be sure, but I'd ask a machinist or very knowledgeable mechanic who rebuilds small engines.
.

[CROSSBOLT]

Two head gaskets are a bad idea since sealing between gaskets is always a problem. It depends upon how much is milled off to get the head flat. The old-timey hot rod engine builders used to put dabs of kid's clay on top of the piston(s), torque the head back on and "bar" the engine over by hand then take the head off and inspect where the valves squished the clay. Shiny spots at the thin part meant the valves probably would hit the piston. The usual fix for that was to mill a "smile" on the piston top to clear the valve(s).

Karl

PS: I must say that Jeff and Wild are the most patient and forgiving men to have put up with this issue without killing someone. I think this has all gone WAY beyond asses and elbows time to be solved.

[wildwildip]

1.) That's the working theory, at least;
2.) You can test the radiator contents for exhaust fumes. There are kits that contain a chemical that will change color to indicate the presence of exhaust gases in the cooling system -- I do not have any first-hand experience with this, but several mechanics have described this to me.

3.) (in answer to compression, stroke, etc. in other post) -- Good questions. I'm guessing buying replacement head & cylinder is the only way to be sure, but I'd ask a machinist or very knowledgeable mechanic who rebuilds small engines.
.

Ok, I will plan on testing the vapors in the coolant for combustion fumes.
If its a negative result I will assume issue with radiator or water pump
If its a positive result I will assume a warped head/cylinder.

Sound reasonable?

[de dee]

  re: the hoses,.  a hose on the suction side could be collapsing at high rpm.

[wildwildip]

  re: the hoses,.  a hose on the suction side could be collapsing at high rpm.

Maybe, however it still overheats at idle.

[wildwildip]

1.) That's the working theory, at least;
2.) You can test the radiator contents for exhaust fumes. There are kits that contain a chemical that will change color to indicate the presence of exhaust gases in the cooling system -- I do not have any first-hand experience with this, but several mechanics have described this to me.

3.) (in answer to compression, stroke, etc. in other post) -- Good questions. I'm guessing buying replacement head & cylinder is the only way to be sure, but I'd ask a machinist or very knowledgeable mechanic who rebuilds small engines.
.

JP you fix your 250S yet?

[mrbios]

Sorry for your troubles.  Long post, here's some thoughts:
 
1. The dealer is weak at trouble shooting - this is normal.

2. Don't guess at whether the head / cylinder jug is warped test it with a straight edge.  Basically a perfectly straight ruler on edge laid against the cylinder head.  There are fancy gauges but this is a start.

3. Pressurize the radiator with a tester and see if the needle falls under pressure which indicates a leak.

4. Compression test dry and wet - provides good basic info about possible leaks - head gasket, valves, total max compression dry/wet (adding a squirt of oil to the cylinder provides a temp seal).

5. Leak down test - look it up, it should have been done and should catch a leak from a warped cylinder / head.

6. Most likely exhaust gas is getting into the coolant.  Consider taking the scooter to a small engine builder - have them tear it down, measure the parts - or send to a machine shop to test if the parts are in spec then they put parts back together if good and replace any if bad (out of spec).

[wildwildip]

The head is in a shop right now for mill work. They are going to remove .002 from it, which is .05 mm, which is the variance the manual calls for oddly enough.
I found a chip in one of the coolant ducts in the head. The shop tech told me it was a scratch? If so no clue how it got there considering I removed the head myself.

Anyway, I will get a new gasket and re install the thing. Hopefully that will correct the issue. I dont know if I should pull the cylinder or not? Now would be the time if needed.... Anyone know?

[wildwildip]

Shop said head was warped, they took .002 off the head, that's about .05 mm like the manual calls for.

Should I have the top of the cylinder checked as well now that the bottom of the cylinder head is fixed?

[wildwildip]

I have also removed the cylinder, it was warped somewhat. About .0015 according to my feeler gage. I am going to take it into the cylinder shop today to see if they can hone the top .0015 off it. I will then use a brand new head gasket and head gasket sealant to fill in any gaps or missed low spots.