Overheated engine

[Eric K]

Yesterday I noticed my GasGas badly overheating while climbing a hill. On the hill it just ran out of power, pinged bad and would not shut off with the kill switch. Prior to that it had some signs of minor overheating – erratic high idle and feeling a bit hot, but otherwise normal.

I checked the cooling system and it was not pressurized so I opened the radiator cap. I could not see any fluid or steam, so I proceeded to add a bit of water. When the water got down to the engine I had a massive percolating boiler spewing steam out the radiator cap. Eventually things settled down and I put in about a quart of water.

At that point I was wondering where the coolant went since I had not had any boiling out. I looked in the sight glass and saw a gray milky liquid. I tipped the motorcycle on its side and I could still see liquid in the sight glass so I assumed the coolant went into the transmission.

I rode easy back to the truck. The motorcycle ran fine with water in it for about 8 miles back to the truck.

At home I drained the transmission. I end up draining 2 quarts of grayish milky fluid out of the transmission. That accounts for where the 1 quart of coolant went – into the transmission to mix with the 1 quart of transmission oil.

I assume the water pump seal failed.

My plan is to…

1) check compression (if good leave the top end as is, if bad rebuild)
2) replace the water pump seal and check for any other potential leaks
3) change the transmission oil and ride it briefly, continue with oil changes until the oil comes out clean.
4) flush out the cooling system and put in new coolant.

Anything else I should look at?

[nhrider]

Originally Posted by Eric K

Yesterday I noticed my GasGas badly overheating while climbing a hill. On the hill it just ran out of power, pinged bad and would not shut off with the kill switch. Prior to that it had some signs of minor overheating – erratic high idle and feeling a bit hot, but otherwise normal.

I checked the cooling system and it was not pressurized so I opened the radiator cap. I could not see any fluid or steam, so I proceeded to add a bit of water. When the water got down to the engine I had a massive percolating boiler spewing steam out the radiator cap. Eventually things settled down and I put in about a quart of water.

At that point I was wondering where the coolant went since I had not had any boiling out. I looked in the sight glass and saw a gray milky liquid. I tipped the motorcycle on its side and I could still see liquid in the sight glass so I assumed the coolant went into the transmission.

I rode easy back to the truck. The motorcycle ran fine with water in it for about 8 miles back to the truck.

At home I drained the transmission. I end up draining 2 quarts of grayish milky fluid out of the transmission. That accounts for where the 1 quart of coolant went – into the transmission to mix with the 1 quart of transmission oil.

I assume the water pump seal failed.

My plan is to…

1) check compression (if good leave the top end as is, if bad rebuild)
2) replace the water pump seal and check for any other potential leaks
3) change the transmission oil and ride it briefly, continue with oil changes until the oil comes out clean.
4) flush out the cooling system and put in new coolant.

Anything else I should look at?

That's not good! Hate to hear this.

I'm bet you'll need to replace the top end. Change the oil with ATF oil and don't even ride it. Run it for a little bit and change the oil. Do that until oil looks good.

Someone else maybe knows my it didn't want to shut off. Air leak drawing in fuel made the engine keep running??? Got me...but I'm sure you'll get an answer.

[mountain thumper]

can a 2 stroke deisel like a 4 strake. my last truck blew a head gasket. it still ran great, but would always deisel for at least 5 seconds after i shut it off. i had just bought a newer one a few weeks before it happened, so i sold the truck( lol for 200 more than id put into it) and never messed with it at all.
in my brain fuel was mixing with the antifreeze, and igniting from carbon deposits inside cylinder(s) that were still hot.

[Skidad]

Don't know about the diesel but they can run backwards. I've seen it happen but never to me. Really funny.


Skidad

[Eric K]

Here is what else I found...

No oil in the cooling system.

Compression measured 182 psi. It was 185 psi just after rebuilding the top end 12 hours ago. (Note: Since my knee was sore, I had my son kick it for the compression check and he did not kick it quite as fast as I did on the previous check.)

The water pump seal was replaced when I did the top end rebuild 12 hours ago. It had worked fine until the last ride. There was no visible damage to water pump seal. The LTR impeller looked fine.

The spark plug looked good - a light brown electrode.

I took the pipe off and looked in through the exhaust port. From what I could see the piston, rings, cylinder, head and power valve look normal.

The exhaust o-rings were the only thing I could see adversely affected by the heat. They were brittle and broke into pieces.

Once I get a new water pump seal it looks like it will take a number of oil changes to flush out the milky gray oil/coolant mix.

Note - this is on the '06 EC300.

[Eric K]

Since the exhaust pipe o-rings were cooked, I replaced the head o-rings. The ‘overheated’ head o-rings were still pliable and intact. There were trace amounts of carbon on the piston and head which I cleaned off. The carbon was baked on.

Here are the compression measurements…

After rebuild ~12 hours ago prior to break in 185 psi (me kicking)
After overheating 182 psi (son kicking)
After overheating and replacing head o-rings 205 psi (me kicking)

I attribute this recent increase in compression to me kicking faster than my son (I have a 60+ lb weight advantage) not to the new head o-rings. I attribute the increase in compression since the last rebuild to ring seating. Overall, great compression and the engine runs just as well as it did before.

The leaking water pump seal did not have any visible damage. The LTR impeller looked fine.

After 3 oil changes with short rides in between the transmission oil looks clean.

I continue to be impressed by the robustness and durability of the GasGas 300 engines, except for the waterpump seal which I have changed a total of 5 times on my ’01 XC300 and ’06 EC300.

[wence]

Had the exact problems you were having on a 98 Rmx 250.
Turns out the head gasket was leaking into the barrel.
Had to reface head and barrel to eliminate warp and replace gasket.This happened on two occasions until doing the head and barrel work.
Good luck.

[Eric K]

The head o-rings were not leaking. I replaced them anyway.

Since replacing the waterpump seal, the engine has not even come close to overheating.

I stuck a temperature tab on the outside of the cylinder just below the head. On high elevation, warm day, tight singletrack, climbing steep hills with many tight 1st and 2nd gear switchbacks the warmest temperature reading was 203 deg F.

The waterpump seal is currently holding up. As long as the seal holds, it works great.