Why is my radiator cap leaking coolant? And am I running lean?

[DSA]

Hi all,

Sulfur yellow 76 GL1000 that I just recently got running after about 2.5 years of sitting. I've got two issues going, and I suspect that they are unrelated. But just in case, I'll cover them in one post here.

1. My radiator cap is puking coolant. This is a brand new cap, this specific one: https://shop.advanceautoparts.com/p/car ... 17110017-P. The seal on the old one was looking really nasty, and I was beginning to leak coolant through the overflow hose. I read that one symptom of that might be a leaky cap, so I went ahead and replaced it. Is this the wrong one or something? It certainly looks like the old one, for what it is worth. Note that this only happens after a longer ride; a 10 minute ride is not enough to make it leak. The old cap did not leak, but it got accidentally thrown out with the trash, so I can't put it back on an check.

2. I think I might be running lean. The bike starts up easily in ~50F weather with the choke. I don't even fully pull the knob out - if I do, the revs immediately jump very high. With the knob partially out, it starts up easily. Within a few seconds, I can push the knob further back in, and seconds after that, it starts accepting gas. At that point, I can push the knob fully in, and can go ride with maybe a smidge of maintenance throttle while idling at a light. None of this suggests to me that I am running lean.
However, while on the highway cruising at about 65-70 mph, the bike's temp gauge shows about halfway up the white area (the first white area; not the smaller one right before the H). It is about 70F today, so not a hot day. On a hotter day, sometimes the fan comes on while on at those same highway speeds, which seems really odd to me. Never had a bike need the fan on on the highway! At lower speeds, say 50 mpg in top gear, the gauge reads closer to the bottom of the white area. But if I'm in the neighborhood at say 20 mph at 2000 rpm, the bike surges a bit. The surge becomes less perceptible the higher the revs and the more the throttle opening.
Finally, and most tellingly: after a 30 min ride with the symptoms above, when I get back home and the bike is idling in the garage (temp gauge halfway up the white area), if I pull the choke knob out, at first nothing happens...but if I continue to do it, the revs go UP.

Penny for your thoughts!

[DSA]

One other piece of info: at my last fill up (almost all leisurely highway miles at 65-70 mph), I got 44 mpg. Not sure if that helps, but figured I would put it out there.

[Fred Camper]

I suspect a head gasket exhaust to coolant leak. That would certainly push coolant out of the cap due to pressure but more likely would look like boiling water in the coolant tank. I certainly would try a known good cap before going after a possible gasket leak.

[DSA]

I actually just did an oil change yesterday, and there was no sign of coolant in there (no chocolate milk) - so at least a coolant-to-oil HG leak is unlikely. I can run the bike in on the centerstand and check for bubbles in the overflow tank.
Do you know if that radiator cap PN above is a good one? Randakk's recommends STANT #10229 or NAPA/Belkamp: 703-1445. I can't find the Napa one anywhere, but this carquest one has the same PN as the Stant - I figured that means they're the same part?

[flyin900]

You may have a bad new rad cap. So it is cheap enough to buy a Stant or a different model as noted in the cross reference for alternate parts that will fit. The running information you supplied seems normal in my books, as it isn't running too high in the gauge area. The fan on while riding is odd at speed in more normal temperatures outside and not 100F in the dead of summer. In stop and go riding in town it will sometimes run, yet I haven't seen it come on during a highway speed ride at regular speeds.

Try a different cap first as the cheapest method to test the system. If you have no coolant in the oil and no bubbles in the system at idle with the cap off once the thermostat is open. You want to look for bubbles in the rad and not the overflow tank, so a careful removal of the cap once the bike is warm, yet allowed to cool a little to let some of the pressure drop. Then carefully remove the cap and start the bike at idle and look for bubbles in the rad coolant. You may get some overflow initially from the expanded hot coolant from the rad, so a catch bucket below is in order.

I would suspect your system appears to be sound overall, yet if a new cap leaks again then further investigation will be warranted.

[Sagebrush]

I replaced a radiator cap on one of my 1100s. It was the right cap but leaked same as yours. I found if I bent the tabs on the underside of the cap to make it fit tighter it cleared up the problem. You may have to play with it a little to get it to fit tight enough without making it so tight you cant get it on.

[DSA]

Thanks for the replies. I took Flyin's advice, and got a new cap: the Napa guy's advice was to forgo the Balkamp and go for the Sankei KH-C13 (Napa PN: ATM1592903. Here's a link: https://www.napaonline.com/en/p/ATM1592903).
With both the Carquest 10229 and the new one in hand, the Sakei looked noticeably sturdier, with thicker sheetmetal forming the cap. It wasn't pricey either, at just over $10. I installed the new cap, topped up the fluid and took the bike for a test ride. Happy to say that the leak is now gone. It also seemed like the bike was running somewhat cooler; the only time it got over halfway up the white part of the gauge was when I was riding uphill at 70 mph. And as soon as the ground leveled off, the temp dropped back down to about halfway and stayed there.
It's too small a sample size to draw any big conclusions from, and worth noting that it was 5-10F colder than when I rode earlier today and saw higher temps + a leak. But will keep this space updated if the temps rise or if it leaks again.

Now...to the running lean part, if that is what it actually is. Would you all expect the revs to rise when the choke knob is pulled out on a fully warmed bike?

[BurnsYoFace34]

So there might be a thread I can't find it but I'm getting coolant in my oil. I've changed head gaskets and sprayed them with the copper coating spray an torqued them to the 42lbs of torque. Still getting coolant in oil. Other than head gaskets what else could I check for

[flyin900]

Now...to the running lean part, if that is what it actually is. Would you all expect the revs to rise when the choke knob is pulled out on a fully warmed bike?

There is a ramp action on the carb bell-crank assembly that takes place when you pull the choke cable out past a certain point that raises the RPM on all carbs properly set up.
As previously noted I think your fine and probably overthinking this if your bike is running well overall. Getting 44 mpg is very good gas mileage and you could pull your plugs to see how they look colour wise if your convinced your lean.
Personally I would ride it and enjoy if your fortunate to live in a warm area and can still ride it now, or year round.

[DSA]

Wouldn't be surprised if I were overthinking - one issue with trying to fix a bike is that you can't switch that side of your brain off sometimes and just ride
I pulled the plugs, but am not sure how to read them. From what I can tell, really the only way to judge the air/fuel ratio from a plug would be to separate the porcelain from the threaded portion, which would destroy the plug. Not that I mind sacrificing a set of plugs, but I'll have to figure out how I want to cut the threaded bit off.
My concern with running lean is that I don't want to end up burning a valve or something. Seems like it'd be a hassle to fix at that point.

[flyin900]

Take some pictures of the plugs and post them for the brain trust to observe them. They should normally be a light tan colour on the porcelain bit when running decent. The ethanol gas these days IMO does change the way they look slightly.
No need to destroy the plug just look at the tip area for signs of a lean condition, which would be a very white porcelain area. A blown head gasket will also clean the tip very white along with the sweet smell of coolant and white smoke from that exhaust side.

[redglbx]

One other thing I will throw out,,, on my 76 I found the timing marks were factory mismarked using a piston stop. The F1/T1 mark was spot on but the F2/T2 mark was about 6 degrees off, correcting this helped the motor run much smoother as you could imagine. My understand is that this is a rare thing and only happened on the 76’s, worth a look when you have time and a few adult beverages.

On the overheating thing, on my 76 it would constantly overheat particularly when running at highway speeds, 70mph was the threshold. Getting sprayed with hot coolant while cruising along at 75-70mph when a hose popped off actually happened.

I went through everything, water pump, new hoses, radiator cap (multiples), thermostats and even had a new higher capacity custom radiator made which I was sure would fix things. It didn’t ! I also replaced the factory fan that was running slower than spec and when allis correct only moves 400cfm with a new pancake fan that moves 1800cfm and has it’s own adjustable thermal switch that you can adjust for on & off settings,,,, still overheated.. (wtf !)

I figured this was all due to the mods I had done to increase the rear wheel horsepower (more power, more heat) but nothing seemed to really help.

So one day with nothing to do and after reading again Randakk’s claim that static timing the ignition like when installing a Dyna ignition over advances the initial timing by 6-10 degrees which is a bunch. So doing a dynamic timing check with a degree wheel found that my initial timing was indeed 10deg advanced and the balance between the t1 & t2 was off as well. So I reset the timing dynamically using a degree wheel on the LH cam pulley and a timing light. I was amazed at how much better it ran and now I will only set timing dynamically ! I also checked that the mechanical advance for proper function, works fine !

The whole point of this long winded story is that now my constantly overheating GL just runs cool, no more overheating. No matter how fast you ride it ! Just a suggestion.

[gltriker]

*Post#13
Here's an illustration I snagged from the Honda GL1000 Shop Manual and marked up its temperature gauge display to add information that isn't shown on the gauge, itself .

See where the fan turns on. " Fan On At 98 degrees to 102 degrees C "

[DSA]

Red: interesting! will do - I haven't set dynamic timing yet. Only static.
Cliff: That looks about right: that is roughly when my fan goes on too. Pretty sure the thermostat is opening at the right time too, as it warms up quickly to that point, and then further heating occurs much more slowly.
Flyin:
Good call, here are my plugs: they're definitely not very tan (very lightly tan, mostly white). They have only got maybe a couple of hundred miles on them. Appreciate any thoughts on these!

[redglbx]

Imho, I would say that those plugs look fine with the bottom one looking a bit lean, maybe. Personally I’d ride the crap outta it and repost those pictures in 1-2000 mi. My .02