Point-Seven-five wrote:First question, is the engine running at normal temperature or is it overheating?

Normal temperature. I installed a temperature gauge and it sits in the middle while riding. Of course that increases somewhat with slower speeds. My fan runs flawlessly and the bike doesn't overheat.

 A blocked radiator will overheat the coolant on a hot day and make it puke out of the overflow.  I had that problem with one of my bikes and had to do a vinegar soak both internal and external to remove the mineral deposits in the radiator and the bugs blocking the fins.

My original 3-core was replaced a couple of weeks ago with a 2-core because that is all I could find. The original had the same issue so I don't think it's the rad. I soaked the 2-core in my bathtub for quite some time and ran hot water through it. I also used the shower nozzle to extensively clean in between the cooling fins.

Second, have you changed the coolant recently?

Yes. It was the same coolant that was in the 3-core and it was fresh. I use Yamalube Yamacool. It's a 60/40 premix.

 It's possible you have an air bubble in the system that is expanding when hot and pushing the coolant out of the engine.  An air bubble can also reduce the cooling capacity of the radiator, causing overheating.

My first thought too. I suppose it's possible but after changing the rad and refilling the system, I squeezed and squeezed and squeezed and...... the rad hoses as the engine was running and coming up to temperature. Saw lots of bubbles. I'd be flabbergasted if somehow there is still air trapped in there somewhere.

Laitch wrote:Like Point-Seven-five, I also think it's likely there is air in the system, escaping as vapor and condensing when reaching cooler air.


Is the fan operating more frequently than usual?

No it isn't. Even though I have a 2-core in it now it seems to behave about the same as the 3-core.


Is there any change in oil appearance?

Not at all.

Were the replacement cap and gaskets OEM?

I think one set was from Euro Motoelectrics and the other from Motorworks.

The coolant level in the coolant expansion tank should be at or near the MAX level in a cold engine before riding.

The manual does actually say to top it up to the MAX mark, so I'll make sure of that before the next ride. Practically speaking, though, you'd think that anything between MIN and MAX should be perfectly fine.

It isn't surprising that the level would be higher in the tank when the engine is hot than when it's cold; that is operating correctly. Coolant is topped up in the expansion chamber, not at the filler neck, on a cold engine.

Yup, just like in any vehicle that I've ever had.

daveyson wrote:I'm pretty sure the filler neck and cap are not original.

The cap isn't as it's the newer style. I still have the original, old style. I've not touched the filler neck so I can't attest to its provenance.


The seals don't look good at about the 7 o'clock position.

I'll have a closer look. I might have another.

I think the level is too low, I adjust mine so that the level is at the full line when hot.

The manual actually says to do that when the engine is cold. Regardless, I will make sure it's topped up prior to my next ride.


I think you got the cap and neck at different times so they might not be compatible, and both might not be compatible with an '85 brick.

I've not replaced the filler neck.

You shouldn't be able to see any bubbles in the overflow tank when the engine is hot or cold, or idelling or at revs.

That certainly makes sense but I've never actually checked.

daveyson wrote:I think you got the cap and neck at different times so they might not be compatible, and both might not be compatible with an '85 brick. 

daveyson wrote:Is that a normal looking cap in the US . . .

daveyson wrote:Is that a normal looking cap in the US, I've got five bricks, none have a cap that looks like that.

https://www.euromotoelectrics.com/product-p/radcap720.htm

The rubber seals don't look good to me. I'd fix that. 

I'd be putting more coolant in the filler neck and overflow tank, and checking for bubbles.

RS Rider wrote:Moments after starting up the bike I got a bubble in the sight tube every several seconds and then what appeared to be a flurry of them when, I believe, the thermostat opened?