Coolant Puke

On my last trip during a short stop I noticed coolant pissing out one of the reservoir overflow lines.

It was far from a hot day but we did have a slow (40 mph) ride through town just prior.

I did not notice the temp gauge going excessively high. When I noticed the fluid coming out, I turned the key back on and it was showing 4 bars and the fan did run. In total I only lost about 300 ml and just

refilled it and finished the trip. Seemed okay on the way home but it did ramp up to 4 bars in the

driveway. Fan kicked on but no more puking.

I have ridden in much warmer locations in stop and go traffic for much longer periods.

I suspect either a faulty thermostat or maybe the water pump. Any others have this issue?

* I am confident that the it was not overfilled, same level I have set it at since new.

Canadian FJR

Is there a thermostat on the bike that might be stuck?

Radiator cap !

Was it overfilled to start with ? If so, you may have not seen this until things heated up and expanded ... Might be nothing to worry about at all ...

After it happened, did the coolant tank go back to the acceptable range or ws it very low ?

Radiator cap sounds like a winner!

FJRBluesman said:

Radiator cap sounds like a winner!

Click to expand...

It has my vote.

Sounds OK sorta...... methinks Ken is right. I'd check that rad cap, but even so, shouldn'ta puked unless overfilled. Weak rad cap mighta let some extra out, but coolant only expands so much, would have to boil.... again if rad cap didn't hold sufficient pressure. If it tests OK, then I'd look at thermostat next. If you open rad cap when not hot and see coolant circulating, water pump likely OK (the bypass hose allows some to circulate even if thermostat closed).

Edit - I see while I was typing others jumped on the rad cap........

I am confident that the level was good before the trip so I'll price up a rad cap and see what happens.

After the puke, filled to midway during the trip when the bike was still warm. Today, completely cool and it is sitting at lower level.

Thanks for the replies,

Canadian FJR

It will be the radiator cap.

If you know how the coolant system works, hot coolant flows into the expansion tank.

As it cools the vacuum draws the coolant back into the system.

With crook rad cap, it fails to refill the system.

Gradually the coolant empties itself out.

Have to remove the dash panel, change out the cap and fill the coolant and give it a good burp, a really good burp, to remove all the air totally, as air compresses under pressure.

So with your explanation the rad will not be full to the top, is this correct?

The rad cap is working like a one way valve?

Canadian FJR

If this helps. You can get the rad cap checked, should hold ~15 psi (or whatever it says on the cap label). When coolant is hot, system is then pressurized to 15 psi which raises the boiling point, coolant then will not boil/puke. Excess coolant will be released to the overflow. When it cools down, as coolant contracts, it sucks in from the overflow reservoir.

On initial fill, underfill it slightly and you'll see the coolant flowing via the bypass, let it warm up a bit (coolant will start to expand), then any time, two or three quick throttle blips will purge the air (coolant level may drop a bit)... thermostat is starting to open. After the purge, top up the rad, put the cap on, run until the thermostat opens fully (some might advise letting the thermostat open then do another purge). I normally overfill the overflow 1/2", then when bike cools down, it should suck in enough to bring the overflow level down to max. Another heat/cool cycle may lower it a tad more, but not much.... then you're all set to go, and overflow is full or just below max. Anywhere between low and max is fine, but I like that max line reference, just me. But, bottom line, for this all to work properly, rad cap must be able to hold the specified pressure.

Normally, the radiator cap will allow pressure to build - up to 15 psi or so. This takes care of letting liquid go to the overflow reservoir when it expands. Under pressure, water has a higher boiling point (even higher with glycol). The thermostat ideally keeps the water from boiling (at the elevated temperature) by circulating through the radiator and switching the fans on, if needed. The only liquid that should ideally go to the overflow reservoir is that due to expansion as the water is heated (should be no steam in the radiator). When the radiator cools, the overflow is sucked back into the rad from the reservoir so there is no air to speak of in the radiator. The reservoir should go from maybe half full when the bike is cool up to maybe 3/4 when hot.

If the radiator cap does not allow the pressure to build to the design level, the liquid in the radiator will boil rather than remaining as a liquid under pressure. The steam will push liquid past the cap into the reservoir; eventually overflowing the reservoir and pissing on the ground. When the system cools, the liquid in the (now full) reservoir will suck back into the radiator but there won't be enough liquid so it will suck air in as well.

Note: The same thing could happen if the rad cap was working but the thermostat was not but you would also have an indication on your temperature gauge. I suppose that in an extreme overheat situation, you could end out with a boil-over where the rad + fan did not have enough cooling capacity to prevent boiling within the radiator. (Make sure the rad cap is on tight!)

Mine did this two years ago, same scenario. I replaced both the cap and thermostat, as I had more money than patience at the time. Problem went away.

Update:

As per Ken's suggestion, I replaced the rad cap. There was some slight debris around the filler so I cleaned that up also.

One other thing that I did was give my rad fins a real good cleaning. First sprayed the rad with brake cleaner then lots of very hot water and soap. The water pressure was low but very hot and lots of it.

I went for a test ride this evening and I am still on the fence if my cooling system is at 100%. It was only 10 degrees Celsius and I need a warmer day before I can sign of on this being fixed.

When I first started the bike it took a normal amount of time to hit two bars. I always let it warm to 2 bars before riding, just something that I have always done.

I then spent some time just cruising downtown with lots of stop & go intersections. The bike stayed at 2 bars. I then played in a clear parking lot doing some 1st gear manoeuvres until the 3rd bar on the temp gauge came on.

Once out on the main road it then dropped back to 2.

A quick run on the highway and then back in town. As soon as I was in town and behind a car the 3rd bar came on again.

One last run out the highway and then I parked to let it idle. It took about a minute for the 3rd bar to come on. I let it idle a couple more minutes to see if the 4th bar and fan would come on but it stayed at 3 bars.

Back on the highway and in 2 km it was back to 2 bars.

It does seem to hit 3 bars much sooner than before but it does drop back to 2 bars once I get rolling so that part is good.

Canadian FJR

If it is hitting 3 bars a bit faster than it used to, it could mean that the thermostat calibration is off just a little bit. Won't hurt anything. Probably doesn't even start to open until 2 bars and might not be as fast or open quite as far as it used to. New thermostat looks like the way to go but I wouldn't bother unless it gets worse. I expect you'll be fine for many miles more.

Thanks Ross. If I can get out on a warmer day then I should know for sure.

Canadian FJR

Sounds normal to me. My 04 behaved exactly the same. Ride more, sweat less.

Canadian FJR said:

So with your explanation the rad will not be full to the top, is this correct?
The rad cap is working like a one way valve?

Click to expand...

Radiator caps are always supposed to work like a 1 way pressure valve.

They are supposed to remain closed to flow out of the radiator until the internal radiator pressure exceed the cap's pressure rating set by the big spring shown below, and then it allows the expanding coolant to flow to the reservoir.

But, they are also supposed to easily allow flow back into the radiator with the least amount of negative pressure (vacuum) when the coolant cools down. This is accomplished with a little poppet valve in the cap, shown as a vacuum valve in the below diagram. It seals under positive pressure, but has a weak spring to be overcome under negative pressure.

If that valve gets stuck it may restrict the flow of the coolant back into the radiator and result in the radiator sucking air in from wherever it can Then further thermal cycles would continually pump coolant out into the expansion tank until it overflows.

My old FJR is now back to normal.

I initially replaced the rad cap because it was easy & cheap (just like me)

This seemed to help slightly but no real warm temps to confirm.

Over the winter I replaced the thermostat and removed / cleaned the rad and replaced the fluid. This

helped but it was obvious that I still had a low speed over heating issues due to a very blocked rad. Blocked from road debris and bent fins.

It was not over heating to the point of pissing coolant anymore but still higher temp that the norm.

I just recently went the next step and replaced the rad ............... life is good once again.

Canadian FJR