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Steaming coolant from lower rear of engine

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I went on a short local ride last weekend, about 10 miles total. It was really slow, through woods where there wasn't any trail, and having to make a lot of U-turns, using 1st & 2nd and lots of clutch.

At one point I tipped over and saw steam blowing out from the lower rear part of the engine, about where the swingarm linkage is. I was right near a large clearing (an abandoned golf course if you can believe that), instead of fiddling with it, I got out on the course to cool the bike down.

I stopped a minute or two later to see if it was steaming, and found nothing. I had burned through an entire overflow tank of coolant during the ride but when it cooled, the radiators were still almost full.

This bike has historically not run hot.. even on long technical rides, I rarely burned through much coolant. In the last few months, I have had the cylinder off once, and the head off once, and installed a HiComp piston.

So, what port is in the rear of the engine to vent over pressure?

Any ideas as to what would make a bike start running hotter than usual?

Thanks guys,

Pete

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base gasket. That would be the main reason for coolant loss other than a hole in the radiator. Unless you have a leak in your overflow which caused it to escape out.

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I had thought of the hose to reservoir (OK, I "hoped" it was that, but think that runs up higher across the frame, but it is something to check.

Base gasket... ugh. I guess it could be that or a head gasket, but I sure dread the idea of taking this thing down again. On a postive note.. It's getting pretty intuitive!

Any other thoughts?

Pete

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OK, it's not the reservoir hose. When I look at the back of the cylinder, I don't see any staining, but I guess it's time to pull it down.

If the base or head gaskets are leaking, will I see any staining or indication which gasket is faulty?

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Clearly a record number of posts in one day for me:

It gets a little weirder. I topped off the radiator and overflow reservoir and ran the bike on the bench in the garage, and let it get hot. I showed 237f on the racetemp strip on the left radiator.

Still no steaming, and even the overflow resv. was completely cool, as if no coolant had moved from the radiator.

I traced the hose that runs from the top of the resv and it drops down precisely at the linkage where I had first noticed the steam the other day.

So let's say the bike is really hot, hot enough to open the radiator cap valve and the steam runs to the overflow resv. Usually, there is coolant in there to condense the steam. But when I dropped the bike on it's side, the coolant was pooled on one side, and the steam just kept going out the upper hose and exiting at the linkage.

That all works, but it doesn't explain why I lost so much coolant in one ride.

Maybe it was just even slower and hotter riding than I realized?

That is all for now, but I'm open to other ideas.

Pete

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You were in first gear way to much and you were using too much clutch. I did the same thing and you'll just have to check the coolant level and just try to get into second gear whenever you can cuz you are bogging it more and your not revving the crap out of it.

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flypigs-

what type of coolant are you using? If not already, switch to engine ice and see if it happens again. Did you change the head and base gaskets when you had it torn down?

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ridin red,

I'm still using regular old green coolant as I always have.

I replaced the base and head gaskets 5-10 hours ago when I did the 13.5 piston, and again replaced the head gasket just an hour or 2 ago when I did the head. I'm pretty sure it's not venting at either of the gaskets as I can see the head gasket is tight everywhere, and the debris that gets btwn the starter and base gasket is all dry. That said, I suppose there could be something blocking one of the cooling tubes causing it to run hotter than in the past.

The more I think about that ride, it was the longest I've spent in 1st gear in a LONG time. Pushing my way through the brush and keeping an eye out for logs limited my speed.

I'll try another ride and I do have some engine ice in the garage that I never found time to add.

Thanks again, and I'll try to post the results of the next ride.

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its possible that you may have put one of the gaskets in backwards or upside down which would block the cooling passages. If your certain that you didnt, I would switch to engine ice. I have lugged in 1st gear for 45 min straight spinning the tire in some gnarly shit and have never overheated my x.👍

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A couple of updates: I ran it on the bench again today, with paper towels wrapped around the cylinder, to see if I could measure any coolant leaking from the head or base gasket. The towels were completely dry, so I don't think it's leaking through either of those gaskets to the outside of the engine.

After 2 cycles of getting it fully hot on the bench, I have lost some coolant from the reservoir, maybe 5mm of height?

Each cycle took about 10-11 minutes to reach 237f on the racetemp strip, and that was with occasional reving of the engine. That seems a bit quick, but not way out of bounds

I checked the trans oil level to see if coolant was leaking past the waterpump seal, but it was normal level, and seemed clear.

So it seems that I have coolant that mysteriously leaves my bike, but doesn't drip or leak to the exterior as far as I can tell.

My thoughts are either that it's spraying a very fine mist from a radiator or hose, and hitting something hot so that I never see it, or a head gasket is leaking into the cylinder, and exiting out the exhaust pipe.

Tomorrow I'm going to see if I can rent a radiator pressure tester to figure it out.

Pete

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if it was coming out your engine you would know it. The exhaust would smell funky and it would be smoking. Let us know what you find with the pressure tester(if you can even fit the damn adapter on the radiator neck!)

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...(if you can even fit the damn adapter on the radiator neck!)

Uhhhmm, adapter? I thought the pressure tester went in place of the radiator cap ?

If that's not the case, do you use a threaded port somewhere? Splice it into one of the hoses?

Thanks again,

Pete

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On my XR650R their is a hose that comes off the overflow tank. The hose runs down the skid plate to the back of the engine/ shock linkage area. I cant see the hose but I know its there.

Could it be that what your seeing is the overflow bottle drain tube blowing off steam and fluid and pressure....????????

Maybe a new radiator cap...????

Also, I had a cracked head which would pressurize the radiator only at high Revs. Going down the straight away it would build up lots of pressure and empty the radiator into the belly pan of my tz250, take a corner and wreck from fluid spilling out on the rear slick.. only did it on the straight at high rmp's

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TZ,

Thanks for those thoughts also. I'm 90% certain that the steam I saw on the ride last week was in fact blowing out the reservoir overflow hose exactly as you suggested. The bigger issue is how I burned through an entire reservoir, and the top inch or 2 of coolant in the radiators in the first 7 miles of that ride and where the coolant went.

If I don't find a leak with the pressure test, the only things I can think of are a new radiator cap, new base & head gaskets, and maybe pop open the water pump just for grins. I just hope I going to find something simple like a hose clamp that is loose. (hah).

Pete

On my XR650R their is a hose that comes off the overflow tank. The hose runs down the skid plate to the back of the engine/ shock linkage area. I cant see the hose but I know its there.

Could it be that what your seeing is the overflow bottle drain tube blowing off steam and fluid and pressure....????????

Maybe a new radiator cap...????

Also, I had a cracked head which would pressurize the radiator only at high Revs. Going down the straight away it would build up lots of pressure and empty the radiator into the belly pan of my tz250, take a corner and wreck from fluid spilling out on the rear slick.. only did it on the straight at high rmp's

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usually the pressure tester that takes place of the cap is large and the ones i have used probably wont fit....

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I couldn't find a tool rental place that had pressure testers, so after many calls trying to reach a human at the local Sears, I found and bought http://www.sears.com/shc/s/p_10153_12605_00946342000P?vName=Automotive&cName=Tools&Equipment&sName=Automotive%20Specialty%20Tools&psid=FROOGLE01&sid=IDx20070921x00003a. Pretty slick little tool, it has a bladder that inflates inside of the neck, so that the right adapter for a particular radiator cap isn't necessary. It also has a set of adapters to pressure test caps to see where they release.

My system isn't leaking. I tested the entire system to 28psi and left it charged for 5 minutes or so with zero drop in pressure. Since I guessed that the cap would release at 15psi or so, this was way higher than the system should ever see. Then I wondered about a head gasket leaking into the cylinder, so I pulled the spark plug and ran the test again with zero drop again.

Finally, one of the adapters did fit the radiator cap, and I tested that and found it released btwn 15-17 psi, which is right in spec.

It's about driving me crazy. I think I'll switch to engine ice, and give it another whirl.

The only jetting I've changed in the last 10 hours or so is that I replaced the air/fuel screw after it fell out during a race. I fished pretty hard, and did pull out the previous o-ring. Maybe it's worth a go to put in the stock screw just to see if that makes it run cooler.

Again, thanks for all of the discussion about this.

Pete

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If it were leaking outside of the engine onto the case/head/radiator/etc it would have a distinct odor when it gets hot. Ever smell a car with a small radiator/hose leak? Same smell. Just a small amount of external fluid and I think you'd smell it when it gets hot. If no smell, it isn't on the outside of anything hot.

Point of reference....my bike doesn't use any coolant. Got it to 208 yesterday. As far as yours getting to 237 in about 10 minutes, if you're not blowing a fan through the radiator when running on bench with some revving, it will heat up quickly because no air is going through the radiator, unless you've got a cooling fan mounted.

I can't see where the fuel screw has anything to do with a coolant loss....

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I'm actually thinking more about the fuel screw, as the timing does work. Since I replaced it, I've only had 2 rides.. the first one for 20 miles total, about 7-10 were technical, and the rest easy, and then the ride that led to this thread. The aftermarket screw had a significantly different shape than stock.

IIRC, the fuel screw adjusts the mixture from idle to 1/2 throttle opening. If it's running significantly leaner than before, that would have me running hot, and just pouring fluid into the reservoir. It wouldn't explain why the reservoir was empty at the end of a ride, but certain explains the radiator being low.

I can't see where the fuel screw has anything to do with a coolant loss....

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I understand about the leaner=hotter, but unless you're running on the pilot circuit, the fuel screw won't matter. That said, if you were just idling along on the ride when it got hot, maybe thats just what you were doing and it would explain the

You've torn your bike apart more than I have, so know more about the gaskets and such than I, so I can't help there. Likely all is ok.

I wonder if perhaps your coolant isn't just old and weak and it all came to a head on your slow ride. Try the Ice (since you have it) and if that fixes it, that was the problem. I just run Honda premixed coolant and it works fine for me so far. Its possible that your addition of the Honda coolant when it was low freshened it up just enough to work again for awhile to lower the boiling point of the coolant, which is what the stuff does when it is good in addition to lowering the freezing point. Once it is weak, it boils/freezes.

Note too that when you add the coolant to the radiator, you need to tip the bike side-side to get rid of any air bubbles in the system. Likely you know that, but it could possibly explain the subsequent coolant 'loss' when it was topped up after the intial incident.

Just ideas. Keep up posted.

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