3YF-'91 General Overhaul

[xtzrick]

The pumping pressure is low, it only has to keep the coolant circulating in the right direction.

You have what is known as a pressurised cooling system, which is why your filler cap has a pressure release valve built into it & the expansion tank. The filler cap/valve is set to release pressure at 14-17psi.
As the coolant temp rises the system pressure rises because of expansion, this pressure is needed to raise the boiling point of the coolant.
So your leaks are reducing the coolant boiling point.

Have you checked your thermostat?
It should start to open between 80-84degC & fully open (8mm) at 95

Rick

[xtrider]

I'd say that noise you were hearing in the hose was the coolant boiling, not good.
First, is your coolant at least 50/50 water/coolant?
Second , you can take the radiator cap off and start the motor, then watch the coolant in the radiator to see if it looks like it is circulating. Don't remove the cap when the system is hot !
Third, are you sure the impeller is turning? (loose bolt/nut, broken shaft ect...)
Fourth, check the thermostat (take it out and try running the bike to see if it still gets hot).

I was at first thinking you maybe was running extremely lean, which will cause it to run hot, but the black smoke out the exhaust says it is running rich.

[xtzrick]

I'd say that noise you were hearing in the hose was the coolant boiling, not good.
First, is your coolant at least 50/50 water/coolant?
Second , you can take the radiator cap off and start the motor, then watch the coolant in the radiator to see if it looks like it is circulating. Don't remove the cap when the system is hot !
Third, are you sure the impeller is turning? (loose bolt/nut, broken shaft ect...)
Fourth, check the thermostat (take it out and try running the bike to see if it still gets hot).

I was at first thinking you maybe was running extremely lean, which will cause it to run hot, but the black smoke out the exhaust says it is running rich.

The 3YF has a seperate thermostat housing with a high neck so viewing flow is not easy.

Easiest way to check the thermostat is by hanging it in a pan of water on your oven hob & turn on the gas, like it says in the manual.
If you don't have any way of measuring the water temp, just make sure your thermostat is fully open when the water starts to boil.

Rick

[xtrider]

So a person can't look down into the radiator through the removed cap and see the coolant churning at least? If not, wouldn't that end up with air pockets that can airlock the system? Until I started casting lead, I never had a thermometer for checking thermostats so I had gotten into the habit of watching circulation(or non if thermostat was stuck< but they usually failed open). For simple trouble shooting overheating I just liked to simply remove the thermostat to see if the motor stayed cooler or ran just as hot, if it ran cooler I got a new thermostat, if it still ran too hot then it obviously wasn't it. Works ok for trouble shooting not precise but pointed in the right direction of what is going on.

[doghouse]

Billy,

Let me know if your still stuck.
I can spare a morning next weekend if it helps?
I'm in East Grinstead so about 30 mins from you.
I spent quite a few months ( and too much money) during the last year putting my 3YF back on the road so may have some insight.
I also have spare clutch bits and I think I have a thermostat somewhere.

Let me know?

Regards,

Adrian

[xtzrick]

So a person can't look down into the radiator through the removed cap and see the coolant churning at least? If not, wouldn't that end up with air pockets that can airlock the system? Until I started casting lead, I never had a thermometer for checking thermostats so I had gotten into the habit of watching circulation(or non if thermostat was stuck< but they usually failed open). For simple trouble shooting overheating I just liked to simply remove the thermostat to see if the motor stayed cooler or ran just as hot, if it ran cooler I got a new thermostat, if it still ran too hot then it obviously wasn't it. Works ok for trouble shooting not precise but pointed in the right direction of what is going on.

The thermostat housing is higher than & connected to the top of the rad so air can escape when filling.


As you can see, in standard form it is single circuit. There's a small bleed hole in the thermostat but no jiggle pin so a small amount of coolant flows through the rad all the time the engine is running which makes it harder to tell if the thermostat is opening by feeling the temp of the top hose

And given the time it takes to get to the thermostat (fairing, seat & tank off then re-fit for a test ride) it is easier to boil a pan of water

Rick

[xtrider]

that's a different placement for the thermostat, don't know if I've ever seen one not bolted to the head itself. Looks pretty inefficient for accurate temp control. We don't have those model over here.

[Worthlessbilly]

Right gents, loads of points to consider there, thank you.
Although the thermostat was functioning correctly before I started monkeying around I'll go with the general consensus and pop out the thermostat anyway, for the sake of isolation of a problem as much as anything else. I'll also have a little think about testing the pump itself for functionality.

I've replaced the jubilee clips and stemmed the leakage from the hoses, however, there's a little coolant still puthering from below the water pump so I'll recheck the seal and the torque on the crankcase and water pump bolts (even if I am a little reticent to pick up the torque wrench again).

Action man was saying that the pump has a differential pressure of .5 -> 1 psi of pressure and that the increase in pressure in the coolant system is caused by the change in phase state of the liquid, so if I were to be losing pressure through leaks then this would make sense. (Now just as a slight aside to satisfy my own interest, if as Xtrider said, it could be the coolant boiling am I right in thinking that the reason the sound stopped when I squeezed the hose because I was increasing the pressure in the system and , thusly, lowering the boiling point of the liquid in there? Or am I barking up the wrong tree as I wouldn't cause THAT much of an increase in pressure. I know I should probably already know this, but I get far to distracted by triple point videos! But I digress...)

Again, through my own lack of knowledge, is the pressure differential that Actioman was referring to (of .5->1 psi) just that of the pump itself in order to creaet flow? If so what is the operating pressure of the coolant system, before it reaches it's critical point and vents through the cap? (Only if anyone knows off hand, I'm happy to ty and look it up if needs be)

Now Rider's point about the engine maybe running lean is a concern for a very specific reason, which I know I'm likely to receive some stick for, but deep breath and here goes: I have "modified" the air box by which I mean I have added a second air filter to the side of the air box. I know I should have looked in to it a lot more and it's a very "teenage boy reading Max Power and fucking up his Vauxhall Nova but it's done. If necessary I can undo this, but only by buying a new side to the box (unless it's crazy expensive then I'll probably unbodge it with some more bodging)

My intention was to just see how it was running and check the spark plugs the adjust the fuel air-mix as necessary, and play around with it. Should I just undo this fuckery before I go any further?

The coolant mix is not 50/50 as the type I've used (and the advice of the bike shop but I'm NOT choosing to listen to them over your good selves) was to fill it "as is" I really hpe I don't have to buy more coolant. I could dilute it after the fact,I suppose if I drained it and measured what's left but I was only going with what the packaging etc. said.

I think it might be quite tricky finding a point to observe whether (or not) the coolant is flowing visually, I'll try and point a torch in to the filler cap maybe but it looks a bit dark and narrow (insert pun here) so a student kitchen is likely soon to be used for the purposes of something other that producing Botulism.

Anyway, all of the points above are on hold because, like a champ, I'v dropped the (Small fuse-looking thing that shields the interference caused by the frequency of spark creation, whose name just escapes me at the moment) in to the spark plug well and am having a fucker of a time getting it out. At this rate I'm just going to flip the bastard over and let it drop our Ockham's Razor and all that.

Doghouse; Yeah please mate, that'd be a massive help. I'll PM you this evening.

[Mezo]

I'v dropped the (Small fuse-looking thing that shields the interference caused by the frequency of spark creation, whose name just escapes me at the moment) in to the spark plug well and am having a fucker of a time getting it out

Grab a length of 10mm dowel or similar and put some blue tack or modellimg clay on the end. Poke it down the cavity and pickup the errant part.

Mezo.

[xtzrick]

Billy
Some coolants come ready diluted some you have to dilute yourself, read what it says on the bottle

The cap vents coolant to the expansion tank when pressure gets to 14-17psi (already told you that )

The pump seal is an "O" ring, if the cover bolts are reasonably tight & it's still leaking you need a new "O" ring not a torque wrench.
If you have to take the cover off you might as well take the complete pump out & check the condition of the plastic drive gear that goes inside the engine.
When you re-fit the pump lightly try turning the impeller to make sure the teeth have engaged, it should not turn just rock slightly.
Then thumb the starter for a second or 2 so you can see the impeller spins with the engine, if it does, your pump is working ok
Re-fit the cover & re-fill after you've checked your thermostat.

Your airbox mod will make the engine run lean.
Duck tape over the holes you cut will let you know if that's the problem (mine ran lean with a better flowing airbox, but I didn't have overheating problems).

XTRider
The remote thermo housing & single circuit cooling system aren't ideal. Normally these engines take ages to warm up because of the bleed hole in the 'stat allowing a constant supply of cool water from the rad, but if they fitted a jiggle pin warm water would not reach the 'stat bulb & you get localised boiling in the head.
It's the lack of a 2nd circuit to bypass the rad that's the real problem. Yamaha penny pinching I suspect.
Google or Youtube "KLR650 cooling mod" & you'll see Kwak owners taking the stat from the head & fitting a remote housing, it's not just Yamaha.

Rick