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After the first 15 hours on my 1991 kdx 200 I noticed that the coolant level in the tank has went from the high to low mark. I didn’t freak out and immediately assume headgasket issue but I decided to look into this alittle further.

The first thing I did was check below the radiator cap while the engine was running. I noticed some frothiness swirling around. I then decided to crack the bleed bolt on top of the left side radiator. The level was below the end of the threads of the bleed bolt so I carefully added some coolant through it and made sure that area burped any extra air was released by leaning the bike over to the right.

I learned that the coolant I am using (engine ice) contains additives that reduce surface tension, which can create bubbles and foaminess. In this case with the cap off running the engine ice is in contact with air which potentially creates this effect.

I’m thinking either the additives in the coolant or the fact that their was an air pocket in the radiator is the cause of the swirl of frothiness I’m seeing under the can and obviously worst case, a minor head gasket issue.

The bike runs great. I have it tuned very well IMO, smooth buildup like a 4 stroke and responsive. I’m trying not to overthink this too much but I find it sort of wierd. What are you guys’ thoughts? Thanks. I have a video of this I will post separately.

Sorry no experience with Engine Ice, for the coolant loss after you bleed the system I have found running anything over about 1" in the overflow tank usually got spilt out the overflow tube of the tank in rough terrain, try running below the low mark for a ride and see if it changes..

Just an FYI, your coolant should just cover the top of the fins inside of your radiators. Any higher will actually cause the excess coolant to be expelled in to the overflow tank.

Now, on to the frothing, yeah, engine ice can do that. I'm not a fan of the stuff and will never use it. I wouldn't worry about your coolant "loss" unless it keeps happening.

JimmyB wrote: ↑12:21 am Oct 16 2023 Sorry no experience with Engine Ice, for the coolant loss after you bleed the system I have found running anything over about 1" in the overflow tank usually got spilt out the overflow tube of the tank in rough terrain, try running below the low mark for a ride and see if it changes..

Ok, I’ll keep an eye on it. Did you mean 1 inch from the very bottom of the tank?

SS109 wrote: ↑01:25 am Oct 16 2023 Just an FYI, your coolant should just cover the top of the fins inside of your radiators. Any higher will actually cause the excess coolant to be expelled in to the overflow tank.

Now, on to the frothing, yeah, engine ice can do that. I'm not a fan of the stuff and will never use it. I wouldn't worry about your coolant "loss" unless it keeps happening.

Every time I checked the coolant level it was right up to the neck when the engine was cold. I’ll keep monitoring the tank and see how low it will actually get before stopping, maybe I can you route the vent hose upward and form a loop to prevent any possible loss through the vent tube.

JZ05220r wrote: ↑08:11 am Oct 16 2023

JimmyB wrote: ↑12:21 am Oct 16 2023 Sorry no experience with Engine Ice, for the coolant loss after you bleed the system I have found running anything over about 1" in the overflow tank usually got spilt out the overflow tube of the tank in rough terrain, try running below the low mark for a ride and see if it changes..

Ok, I’ll keep an eye on it. Did you mean 1 inch from the very bottom of the tank?

Yes only a inch in the bottom of the overflow tank, personally I fill the rads full, as the coolant heats and cools it flows back and forth into the tank back to the radiators/motor.

How is your overflow tank's cap's gasket? Someone I know (COUGH) once forgot to put the gasket on, and it would leak out the cap.

Put a paper of some sort to see if it is coming out of the overflow hose.

KDXGarage wrote: ↑02:14 pm Oct 16 2023 How is your overflow tank's cap's gasket? Someone I know (COUGH) once forgot to put the gasket on, and it would leak out the cap.

Put a paper of some sort to see if it is coming out of the overflow hose.

Their is a rubber dome seal under the cap I believe but I can check.

I decided to crack the bleeder screw on top of the cylinder to see if I could see any bubbles before the coolant started spewing. There were initially some bubbles then it was just straight coolant coming seeping. I’m very annoyed with my luck in case this is another headgasket issue.

Yes, the rubber dome piece. Thanks for the clarification. I looked it up. That part number goes from 1988 - 2023 on various bikes, so us E owners should be in good shape on that part for years.

No problem, glad to see the part is still available. I just took it for a 15 minute ride around some fields and trails.. Anyways I taped some napkins to the overflow vent hose and this is what I saw. Their is in fact coolant coming out of the overflow vent, even with the coolant level below the low marking. Got on it hard a few times and I smelt no coolant from the exhaust, smells good like a 2 stroke should. The hotter the engine gets/harder I ride , the less it smokes which is related to the way I have it jetted. Still confused about seeing some air in the system when cracking the bleed screw earlier. I think I’ll keep riding it and see if the coolant level in the tank reaches a stand still.

JZ05220r wrote: ↑08:11 am Oct 16 2023

JimmyB wrote: ↑12:21 am Oct 16 2023 Sorry no experience with Engine Ice, for the coolant loss after you bleed the system I have found running anything over about 1" in the overflow tank usually got spilt out the overflow tube of the tank in rough terrain, try running below the low mark for a ride and see if it changes..

Ok, I’ll keep an eye on it. Did you mean 1 inch from the very bottom of the tank?

No, I was speaking of in the radiators themselves when the bike is perfectly vertical. I have never had the overflow tank on any of my KDX's and never had a problem with coolant loss.

SS109 wrote: ↑05:37 pm Oct 16 2023

JZ05220r wrote: ↑08:11 am Oct 16 2023

JimmyB wrote: ↑12:21 am Oct 16 2023 Sorry no experience with Engine Ice, for the coolant loss after you bleed the system I have found running anything over about 1" in the overflow tank usually got spilt out the overflow tube of the tank in rough terrain, try running below the low mark for a ride and see if it changes..

Ok, I’ll keep an eye on it. Did you mean 1 inch from the very bottom of the tank?

No, I was speaking of in the radiators themselves when the bike is perfectly vertical. I have never had the overflow tank on any of my KDX's and never had a problem with coolant loss.

Gotcha, my ktm doesn’t have an expansion tank as well so I know exactly what you’re talking about. If I delete the tank. I’d probably just let the coolant spit out onto the ground as it warms up. Engine ice is biodegradable.

How is the overflow hose routed?

Hopefully it is just leaking there and not internally.

Good question, just looked at the routing diagram. #4 is the breather vent hose. It looks like it makes its way up the frame toward the gas tank. Mine is routed down toward the left toward the swing arm. Maybe that’s part of the problem. Not sure where the vent hose should actually end if going up the frame.

JZ05220r wrote: ↑07:42 pm Oct 16 2023 Good question, just looked at the routing diagram. #4 is the breather vent hose. It looks like it makes its way up the frame toward the gas tank. Mine is routed down toward the left toward the swing arm. Maybe that’s part of the problem. Not sure where the vent hose should actually end if going up the frame.

The overflow hose(#4) from the tank runs over the top of the rear fender just behind the rear airbox bar out the right side of the frame, you can sort of see it in that photo, I don't remember where it went after that. If you have the tank might as well use it, just keep a small amount in it and it will draw the coolant back and forth. If you get in a slow section and the engine starts to overheat the coolant flows into the tank, get onto a logging road the engine cools down, draws the coolant back. I don't think I add even 2 ounces a year in riding.
I have never seen anyone remove the overflow tank from their car/truck, it serves a purpose, you have it why not use it.

JimmyB wrote: ↑09:09 pm Oct 16 2023

JZ05220r wrote: ↑07:42 pm Oct 16 2023 Good question, just looked at the routing diagram. #4 is the breather vent hose. It looks like it makes its way up the frame toward the gas tank. Mine is routed down toward the left toward the swing arm. Maybe that’s part of the problem. Not sure where the vent hose should actually end if going up the frame.

The overflow hose(#4) from the tank runs over the top of the rear fender just behind the rear airbox bar out the right side of the frame, you can sort of see it in that photo, I don't remember where it went after that. If you have the tank might as well use it, just keep a small amount in it and it will draw the coolant back and forth. If you get in a slow section and the engine starts to overheat the coolant flows into the tank, get onto a logging road the engine cools down, draws the coolant back. I don't think I add even 2 ounces a year in riding.
I have never seen anyone remove the overflow tank from their car/truck, it serves a purpose, you have it why not use it.

Oh yea… you can prob see how I was looking at the diagram now but your are right it does go right over the rear fender along the bar behind the air box. I agree I’ll probably keep it. I’d really like to know where the hose continues outside of what the diagrams showing.

I do have the mityvac cooling system pressure tester but I need to replace the gauge as it is leaking for an area I cannot reseal.

I will bet one crisp dollar that your radiator hose pointing down is the cause. I think I did it that way and suffered myself many years ago.

Look in the OEM service manual for how a new bike has the hoses routed. I do not mean by the routing diagram, but by looking at the pictures where they are working on the bike with the seat off. I have done this before to learn how it was when new.

EDIT ADD ON:

Look at the shock linkage arms pictures. It is ran in front of the right dog bone.