Overheating after valve check...any ideas?

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WTP07

WTP07

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As the title says...

I just finished the valve checks and once I had it all back together, I topped the coolant back up and filled the overflow bottle. Ran it until the fans came on, and expected the temp to drop once they kicked in. Temp kept climbing and once it hit the top bar, I shut the engine off and then turned the key back to run to help cool things off a bit. ( I know this just cools the coolant in the rad, but every bit helps I figure)

Any ideas why it's doing this? When I rode in some brutal heat last year (33ºC/90ºF) every time the fans kicked in the temp would drop, even if I was stopped in traffic and there was no airflow over the rad. Shop ambient temp yesterday was about 15ºC/60ºF, so that should have helped somewhat.

Do I have an air bubble trapped somewhere, or could I have screwed something up when I reinstalled the cooling tube that goes over the valve cover?

Thanks for the help folks!

Randy.

 
How does an air bubble persist in a cooling system? Wouldn't the air be pushed along by the coolant behind it until it got to the radiator?

 
Last edited by a moderator:
Ignacio said:
postoak said:
How does an air bubble persist in a cooling system? Wouldn't the air be pushed along by the coolant behind it until it got to the radiator?
Click to expand...
Try searching on +air +bubble +cooling. 2 pages of threads covering the subject. Talked about many, many times on this forum.
Click to expand...
I figured it out after thinking about it. Maybe he could elevate the rear of the bike so that the top of the radiator is lower than the fill level?

 
postoak said:
Ignacio said:
postoak said:
How does an air bubble persist in a cooling system? Wouldn't the air be pushed along by the coolant behind it until it got to the radiator?
Click to expand...
Try searching on +air +bubble +cooling. 2 pages of threads covering the subject. Talked about many, many times on this forum.
Click to expand...
I figured it out after thinking about it. Maybe he could elevate the rear of the bike so that the top of the radiator is lower than the fill level?
Click to expand...
If you fill via the overflow tank to the "full" level, you have to run the engine up to where the fans come on, shut down and then let it cool to suck the fluid back into the radiator. Refill to the "full" line and repeat until there is no change. Better to fill via the radiator cap and run the engine to "burp" any bubbles and then top off the rad via the rad cap. Then fill the overflow tank to the appropriate level.

To the OP, I usually do a complete cooling system drain (and plug change) whenever I do a valve check. Timing for those services work well for the FJR - even if the plug interval is a lot longer than suggested by Yamaha. As far as the overheat after the valve check, air in the radiator is the most likely cause; especially since nothing was done with anything that is likely to affect timing.

I suppose that there could be a problem with the thermostat, water pump or the temperature sensor itself but I think these things are far less likely than air in the system.

Edit to add: Make sure that the radiator cap is fully tightened (and functioning properly). If not, the radiator won't develop pressure properly. Also, fluid in the overflow bottle won't suck back into the radiator as the engine cools if air can get in around the cap.

 
Last edited by a moderator:
RossKean said:
postoak said:
Ignacio said:
postoak said:
How does an air bubble persist in a cooling system? Wouldn't the air be pushed along by the coolant behind it until it got to the radiator?
Click to expand...
Try searching on +air +bubble +cooling. 2 pages of threads covering the subject. Talked about many, many times on this forum.
Click to expand...
I figured it out after thinking about it. Maybe he could elevate the rear of the bike so that the top of the radiator is lower than the fill level?
Click to expand...
If you fill via the overflow tank to the "full" level, you have to run the engine up to where the fans come on, shut down and then let it cool to suck the fluid back into the radiator. Refill to the "full" line and repeat until there is no change. Better to fill via the radiator cap and run the engine to "burp" any bubbles and then top off the rad via the rad cap. Then fill the overflow tank to the appropriate level.

To the OP, I usually do a complete cooling system drain (and plug change) whenever I do a valve check. Timing for those services work well for the FJR - even if the plug interval is a lot longer than suggested by Yamaha. As far as the overheat after the valve check, air in the radiator is the most likely cause; especially since nothing was done with anything that is likely to affect timing.

I suppose that there could be a problem with the thermostat, water pump or the temperature sensor itself but I think these things are far less likely than air in the system.

Edit to add: Make sure that the radiator cap is fully tightened (and functioning properly). If not, the radiator won't develop pressure properly. Also, fluid in the overflow bottle won't suck back into the radiator as the engine cools if air can get in around the cap.
Click to expand...
Thanks for the help. I did the plugs when I did the valve check, just makes sense. Turns out it was a good idea, gaps were all way bigger than they should have been. It's a snow day here is SW Ontario, so I will be working on it later on. Hopefully this is an easy fix. I appreciate all the help folks!

 
In the immortal words of Mr. Harvey, what about the "rest of the story".

I'm particularly interested in whether or not the bike actually overheated? If the air bubble was trapped in the cooling pipe, plausible on a number of levels, then could the sensor have been reading the "air" temperature of the bubble, which should be higher than the temperature of the more conductive coolant?

 
WTP07 said:
Thanks fellas. All fixed up. Must have been an air bubble. Drained, refilled it SLOWLY ...ran through several fan cycles. Beauty! Throttle body sync left then I can button her up and wait for warmer weather!
You guys rock!
Click to expand...
Yep, that 's the trick- fill it very slowly. When I replace my coolant I:

- remove the overflow bottle and wash it out with mild detergent & a bottle brush. It gets cloudy if you don't;

- refill overflow to 3/4" OVER the full mark prior to starting the first time. The level will be perfect after.

Now that you've already run yours, if you decide to clean the overflow reservoir, refill it to just the proper level and it'll be fine.

 
<blockquote class='ipsBlockquote'data-author="philter" data-cid="1413343" data-time="1550000104"><p>

AND, what type of plugs did you use? Were the old ones the right color, just with an extra<br />

large GAP?</p></blockquote>

Yes, replaced with NGK Iridium, same as we're in there. Colour was fine, just too large of a gap. Either installed wrong or wear. Impossible to tell at this point.

 
<blockquote class='ipsBlockquote'data-author="hppants" data-cid="1413338" data-time="1549994102"><p>

In the immortal words of Mr. Harvey, what about the "rest of the story".<br />

<br />

I'm particularly interested in whether or not the bike actually overheated? If the air bubble was trapped in the cooling pipe, plausible on a number of levels, then could the sensor have been reading the "air" temperature of the bubble, which should be higher than the temperature of the more conductive coolant?</p></blockquote>

I assume that the temp sensor was reading steam at the highest point in the cooling system. Once it hit the top bar on the gauge, I shut it down. Never got more than 2 bars above the 1/2 way point today. Doubtful the engine got anywhere near overheated last time.

 
Ummmmm...... you aren't supposed to gap iridium plugs. Install as they come. (With a larger gap than specified for normal plugs)

 

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