Cooling system woes: Overcooling, coolant loss, gauge problems? - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 20 (permalink) Old 09-12-2017, 08:48 PM Thread Starter
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Cooling system woes: Overcooling, coolant loss, gauge problems?

Hi all, time for my next weird issue.

Again, I hope this is only a weird issue to me.

The Vulcan is running great, I think I chased down it's electrical gremlins related to lighting, and now I'm dealing with some cooling system oddities. I think I have two issues. One related to temperature indication, and another related to a slow loss of coolant. In my best case scenario, I think I have slow leak somewhere, and a bum gauge, and it actually is running at correct temperature.

What I've seen:

The system loses an amount of coolant about equal to half the distance between the low and full mark on the coolant bottle per 50 miles. I have neither smoke nor sweet smell in the exhaust. I've already replaced the radiator fill cap after the old one tested bad, the problem remains.

The temperature gauge barely moves. Maybe a needle's width off of where it is when the bike is off. It doesn't matter what traffic or what I'm doing at the time, I've never seen it past there.

The temperature gauge tests good. Sort of. I think. I turned the ignition on and ran the yellow lead off the top of the thermostat housing to the negative terminal on the battery, and over the course of 15-20 seconds the gauge slowly swung from C to H. When I removed the lead, it swung back to C, maybe just a tinier bit faster. Should this be swinging more quickly? Could my indication problem be a reluctant gauge?

The thermostat tests kind of good. By which I mean it's in the ballpark. I just had a meat thermometer to check temperature in my hot water with so there could be some amount of error margin there. It started opening between 185 and 190, probably didn't have 8mm (per the manual) by 200.

Last I changed the oil, it was gassy, due to a carburetor problem, but not even a little bit milky. Bike has been run ~200 miles since then. I know my coolant is going /somewhere/ but I don't think it's a head gasket issue.

Coolant was recently changed and radiator flushed with demin water and Walmart brand Green (that specifically states safe for aluminum engines on the bottle). No large chunks came out, just some cloudy green coolant. Also I got drainage from both drain holes on the cylinder, the one on the bottom, and out of the radiator, no apparent blockage. When I refilled, I used the "refill slow and shake the heck out of it" method to eliminate air bubbles. When I bled using the screw after the fact, pretty much no air came out (but it's a little tough to see since I had to pull the bleeder completely to get any flow. I think I have another around here somewhere....). The Coolant pipe from T-stat to radiator had a couple chunks on it when I pulled it, and that hose line had no clamp. Are these hose lines sensitive to missing clamps? I also noticed the O-ring for the pip going from T-stat towards the back of the pipe is somewhat deformed. It's not ripped or torn, but it definitely has a "flat" side on the one side where the pipe was pressed against it. The T-stat o-ring is a little ripped up looking, but I haven't specifically noted any moisture seeping there, or anywhere else. Is this a common place for a hidden leak since it's so close to the head? I guess it could evaporate fast and it's not exactly the most visible.

The bike is not running in anyway that indicates dire overheating. No steam, no stumbles, it's consistent from mile 1 to mile 30 of getting to work. Currently I have the thermostat housing and filler neck sitting on my dining room table and I'm checking it out, I may just replace the thermostat while it's out (Honda Accord, 79-88, right?).

Thanks in advance for any insight or advice! This bike gets more fun to ride with everything I fix, I just don't want to have to worry about going dry on coolant and burning it up!

1993 Kawasaki Vulcan 750

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post #2 of 20 (permalink) Old 09-12-2017, 09:50 PM
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If the coolant is not going to the oil, and not running out somewhere, it just about has to be burning it. Check real close around the cylinder base gaskets and the o-rings where the coolant pipes go into the jugs.

Gauge test - Slow change might be normal, but it might swing quicker if it's not connected to the sender while testing.

Sender test - Disconnect gauge wire, read ohms on the sender as the engine warms. Probably would need a wire run off the sender to stick out under the tank. Ohms should change quite a lot between cold/hot. Exact ohm range might be in the manual. Or, can use a pan of water like testing the t-stat. Sender sounds like the culprit with the gauge not reading, assuming there's no air in the system.

T-stat - sounds like it's ok.

Did you bleed air after the engine warmed up and radiator was full? Needs that.

Search for wet spots about 10 minutes after a long hot ride. (no puns intended)

Sometimes I use glass or a mirror to check for moisture in the exhaust. If the exhaust fogs the glass right after a hot run, it's burning coolant.

Also, try to check the coolant temp with the thermometer. If the coolant is hitting 180-190, very good chance the sender is bad, because the gauge seems to be working. Most of our gauges run at the midpoint for normal temps.

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post #3 of 20 (permalink) Old 09-13-2017, 12:39 PM
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Check for coolant leaking from the bottom of the engine. There is a "weep hole" directly under the water pump. Hot engines tend to boil off the little drips quickly so look carefully, mine dripped just enough to mark a sheet of cardboard i put under it when parked but lost noticeable amounts of coolant when riding.

Suspect you have a sender problem as well.

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post #4 of 20 (permalink) Old 09-15-2017, 05:11 PM Thread Starter
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Definitely all things I need to look at. I ordered new gaskets since the old ones were chewed up, so once those come in I'll be putting the pieces back together and seeing how it goes. Holding pattern till then.

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post #5 of 20 (permalink) Old 09-17-2017, 09:04 PM
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if you don't see the coolant it is coming out of an area near the engine and evaporating before you can see it. If it were the overflow it would be under the bike when it is parked. The hose that runs under the tank is the most neglected because of how hard it is for the average user to inspect. I'd suspect you could have a leak where the hose connects to the thermostat housing and runs to the back of the bike or a possible small leak that is about to become larger very quickly if it is the hose. Second are is the previously mentioned coolant hoses running into the metal pipes that connect to each head. They tend to leak and the o-rings are typically neglected in them. Both of these are above the engine and leak down onto it and evaporate causing a ghost coolant effect where it disappears.


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post #6 of 20 (permalink) Old 09-27-2017, 07:59 PM Thread Starter
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Ok,

So I've gotten the thermostat back together and on, and I'm slowly learning some things.

1) The biggest bummer, I do have seepage at the base gasket. It seems like barely any so once I recover from the other things going on, I may evaluate a "just live with it" approach. That's small potatoes right now though.

2) Either my temperature sender (at the thermostat housing), or my temperature gauge itself are bad.

3) My fan does not come on.

4) Other wise running well.

I took the bike out for a ride and aside of one abortive attempt at a ride where I realized I had forgotten to tighten down the bleeder (turned about, headed home, and tightened that right up). It went quite well. I did 40 miles of varied suburban and rural roads, some state routes with light traffic, some neighborhoods, no issues. Then I headed into the city to visit my cousin in the hospital and I got bound up in traffic.

I understand these bikes don't do well in traffic. I was stopped in traffic for about 5 minutes, and it was nearing 90 degrees out in the sun, when all of a sudden I see a spurt of coolant out the reservoir overflow house (based on the way it is routed, really it more sprayed on my leg/on the exhaust). I immediately killed the engine and duckwalked my bike to the traffic light that was holding everyone up. Once I was at the head of the line there and had a green, I fired it back up and traveled the block and a half further I had to go (fortunate there...). I parked the bike and just headed into the hospital. No way was I going to mess with a hot coolant system. Before walking away from the bike I opened the reservoir bottle to see it boiling vigorously in there. So, yeah. Definitely overheated. My temperature gauge through that all didn't move past the second white tick mark on the left side of the gauge. Hence why I believe my sender or my gauge itself to be failed.

After I left the hospital (2.5ish hours later), I walked to a conveniently located (8ish city blocks) Pep boys, picked up a gallon of premix and a screwdriver and walked back to the bike. I filled the filler neck slowly, shaking the bike vigorously to help eliminate air voids. Once the level in the filler neck didn't go down at all upon shaking, I filled the reservoir to full and rode for home. The ride home was uneventful and quite nice since rush hour traffic had abated and it had cooled off significantly. It seems like I have no issues with overheating until I'm stuck in traffic with a nonfunctional fan (hopefully).

At home, I checked the fan. Nothing when I grounded the temperature switch on the radiator, but when I put 12V across the fan itself, it turned on just fine.

So here's what I think happened. I got jammed up in traffic and overheated. The fan never kicked on because my relay is fried (I've had other issues with the junction box, so this isn't a surprise), and I didn't see it warming up because my temperature indication is messed up. In the original post I describe the gauge's behavior to being grounded. Swings to hot in 15-20 seconds. So it will /eventually/ make its way there. I don't know if this is normal behavior. Does anyone know, or is willing to test the gauge on their ride for me? I just need to know how fast that needle swings when the gauge is grounded with the ignition on. I don't want to just hurl parts at this. It's either the sender or gauge (or possibly both I guess).

For the fan relay, I'll just buy a 5V 30A relay and wire it in. That's not a big deal. I've seen it described elsewhere on this site and I'm comfortable with finding parts and following the general guidance I've seen to get that rigged up.

For the seeping base gasket, I take it replacement of the gasket is the only true fix. I'd rather not pull the engine just right now, but it's a repair I can plan for. Is there anything else that can help with the seepage in the meantime that people have tried? I really don't want to pour anything into the coolant system unless it's tried and true and well supported by this community, but I figure who knows, maybe it turns out the going repair for this seepage is a generous helping of flex-seal. (You laugh, but we've discussed using it on minor leaks in the nuclear power plant I work in too, so you never know). In the meantime, a few teaspoons of diluted coolant concentrate/50-100 miles isn't a big issue so long as I keep an eye on it.

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post #7 of 20 (permalink) Old 09-28-2017, 01:01 AM
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I've used sealers, but wouldn't do it on this bike.

Try this for the fan:

Connect a ground jumper wire to the fan switch.

Find the blue wire on the JB plug. Think it's the top plug but do both, the other blue wire is the headlight wire. Wiggle the blue wires in/out and side to side, see if the fan kicks on. If the fan runs, the spade is loose. Have to release the tiny plastic tab in the plug to unlock the spade, then squeeze the spade so it fits tighter. Mine did that.

With no fan, you need to run at least 30 mph to keep it cool, it won't take sitting in traffic. With the fan working, mine stays cool in all conditions.

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post #8 of 20 (permalink) Old 09-28-2017, 08:55 AM
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Maybe applying a nice flexible hi-temp epoxy (JB weld or similar) to the weeping portion would help? It can always be removed should you decide to tear the motor down and replace it.

As for the fan kicking on, you could also just put a switch somewhere and activate it manually whenever you slow the bike down. I know a couple of users here have done that 'cause they don't trust the temp relay to kick it on

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post #9 of 20 (permalink) Old 09-28-2017, 09:10 AM
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also make sure no coolant is seeping into the oil

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post #10 of 20 (permalink) Old 09-28-2017, 09:46 PM Thread Starter
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@spockster No matter how much I wiggled that wire, I couldn't get the fan to kick on while grounding the signal wire. I just went and bought a relay, fuse holder, and some fuses and went to town. My bike now has an independent fuse for the fan that behaves correctly when I ground the signal wire.

I don't know if it behaves properly at temp. Guess it just depends on if the temperature sender in the radiator is working (the way this bike is going, I give it about 50% chance). I won't know till I take it out and let it heat up. Maybe I'll just let it idle for a while tomorrow afternoon. I'd really like to have a functional temperature gauge before I do that though.

Has anyone had a chance to check the behavior of their gauge when grounded yet? Or just know how it should behave?

I may try some high temp epoxy. I'll have to see just how much it is seeping first.

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