Gl 1500 slowly overheats at idle.

[Weavetron]

Hi,with the info on this website I have been able to get a 2000 gl1500 se running again. After sitting for 10 years. In a garage luckily.I’ve done the timing belts,the fuel pump and carb overhaul. I’ve bled the rear brakes,took about a week to get any rear brakes at all. I haven’t spent the 600 bucks on new tires yet. I’ve got 100 miles on it, staying close to home. Today was one of the longer rides, practicing slow riding stuff. Back on the road, I stopped for minute. Thought I smelled coolant,which is new and full. The fans are on but it’s close to H so I head home,let it cool off. Come back later,starts normally and warms up fans come on about 3/4 gauge stay on briefly. Moment later that repeats, but when they come on the 3rd time they stay on and the temp slowly increases. I know that’s not right so I shut it off. Both radiators are hot, both fans are on. All the coolant lines are hot. On the road temp has not been a issue,always seemed too cool. I work on cars where correct temp is important. So my question or thought is “has the water pump worn out” it appears to be a rubber impeller that can be replaced. Is this something that can happen. On maybe thermostat is only partially open. I want to take apart the water pump to inspect but then I At least need gaskets to reassemble. Any silver bullets anyone?

[gford]

Make sure the rads are full of coolant and have been burbed properly. Run the bike with the rad cap removed and watch for air bubbles at the rad neck when you rev up the bike. If you see coolant moving this will confirm your water pump is working. If this checks out the next thing would be your thermostat.

[Weavetron]

Thanks, that’s the kind of insite I’m looking for.

[Weavetron]

Warmed it up with cap off. I saw several nice big bubbles, thought that looks good. But coolant kept getting hotter, some decrease when fan came on. But after a few fan cycles coolant temp was going up instead of down with fans on. Slowly but definitely going up. I’m going after thermostat now.

[MikeB]

From what I have seen in the past, nice big bubbles coming up to the radiator filler neck and the coolant temperature continuing to rise at idle with the fans running is an indication of a head gasket leak. Compression gasses will leak by the head gasket and heat the coolant. The bubbles made by the gasses are what is seen at the filler neck. Or even worse, it could be a crack in the head causing the problem.

[Weavetron]

Thanks for the response,that did go through my mind last night. Do you think that could be confirmed with a “ block check” tester? I’m going to contact PO and see if he can remember why it got parked in the first place.

[jonnich93]

If you smell coolant check hose from radiator to reservoir, they crack and leak. Check thermostat.

do little things first.

[MikeB]

A Combustion Leak Test Kit, https://www.amazon.com/Block-Tester-BT- ... B06VVBSFTF, can tell you if there is a combustion leak into the coolant.

[Weavetron]

Short update. Removed thermostat and tested. Over 200 deg water,t-stat never opened at all. I put in new t-stat, Napa 101. Now,the fans cycle a few times then they stay on, but the temp is more stable. Before the temp would just slowly increase. This is all at idle. P.O. Said there were no issues when bike was parked 10 years ago, at 65k miles. Fingers crossed. Now to reassemble. Thanks for the feedback everyone.

[DenverWinger]

On my 1500 I can see 3/4 scale on the temp gauge if I'm stuck on a hot summer day in stop/go commute traffic on my 1500, but it doesn't go over that... Cruising down the road at speed it stays around 1/4 to 1/2 scale depending on conditions. Higher if you are stopping often or driving slow.

Gotta love stuck thermostats.

A few years ago I had a thermostat stuck open in my Toyota car. in middle of Winter. No warm place to work on it' so I just stuck some cardboard in front of the radiator blocking enough air so it would warm up some while driving back/forth to work and it was OK. Kept a good eye on temperature gauge to be sure....

But one day I decided to go to Silverthorn CO, crossing the continental divide. Thermostat still stuck. Temperature gauge got a little warmish climbing up to Eisenhower Tunnel (at some 11,500 ft elevation) (still middle of Winter and still cardboard in front of radiator), but on the downside it was a different story.

It's a steep downgrade for five miles, and you have to downshift a couple gears to keep the car (or bike) from running away from you. In my 5-speed manual Toyota in 3rd gear, by the time I got to the bottom of that downgrade, the temperature gauge was pegged on "cold" and there was no heat in the car whatsoever!

[Weavetron]

I have no one else to tell this to. So with a new thermostat things seemed better. I go ride it,after about an hour riding each time I come to stop the temp climbs into the red, fans have been put on a switch to eliminate thermal switch. So fans are on all the time. Back home I brought it up to temp with radiator cap off. I used digital cooking thermometer it was showing over 230 in fill neck and I checked it with a co2 detector I could not get it to test positive for exhaust gases in coolant, and I’ve never experienced a single cylinder misfire on cold start. I’m seeing 230 at the radiator with a temp gun.today I checked waterpump and it’s in good shape. Tight,no wear. I’m stumped, could it/ is it the head gaskets? I know some cars can how bad head gaskets and not test positive for exhaust gasses in coolant… oil looks good and coolant looks normal,any how, thanks for reading.

[DenverWinger]

Last year I got caught in Chicago Friday Rush Hour, around 5pm. Traffic was go 5mph about 50ft and stop again. Surrounded by Semi trucks. 95 degrees outside temperature. Pulling fully loaded camper trailer and 2-up. "Precious Cargo" Deb riding pillion growling in my ear about the traffic even louder than the all the noise from the Diesel semi's surrounding us. And temperature gauge on the bike only a needle's width below the red. Fans running constant.

Thankfully no steam, engine wasn't boiling, but way hotter than I'd ever seen. Thought about pulling over somewhere, but "no steam" and not quite into red on Temp gauge said bike was still OK and we could keep going. Temp gauge back to "normal" range after we got out of mid-town Chicago and resumed speed.

Found out later that the coolant reservoir was empty (my fault, didn't check before the trip and the bike leaks a little in cold winter months) so the radiator was probably not completely full.

230 degrees is not absurdly hot. My Jeep with temperature gauge normally shows 220 on regular average driving. If your radiator cap can hold correct pressure it will be over 260 degrees and 13-15 pounds of pressure in the cooling system before you are truly overheated and start blowing steam.

My bike cruising down the highway on an 80 degree day will read about 1/3 scale, prolly 210 degrees.

If I let bike idle for extended time just sitting (I was blasting the stereo in the park on a hot day) temperature gauge was sitting around 3/4 scale and fans on constant. This with coolant full. A bit hotter than normal city driving on a hot day (normally half-scale or a little higher), but nowhere near overheating. If I had to guess, 230-240 degrees. Maybe even 245. But not 260.

Is it possible your temperature sensor is failing, and reading hotter on the scale than things really are?

You aren't really overheated until there's steam coming out the overflow. If no steam, cooling continues. But if the pressure cap is not working to spec, or radiator is unable to cool the liquid then coolant turns to steam and over-pressures the radiator cap, boils out of the engine and you have thermal runaway and you are officially overheated.

[Weavetron]

Update with fix. I inspected the waterpump, looked like new. So I reassemble everything,verify it still runs hot after 20-30 minutes. I took it to work to “sniff the radiator” for hydrocarbons,none detected. Re check hose and radiators temps. Bam, cold spot in the middle of the radiators. When I removed them,the very last bit of coolant out of the top of the radiator had stuff in, like pile of rock salt in my hand. Ok clogged radiators, I missed that clue before. I tried to clean them with vinegar, like I did with gas tank off a sv650. Worked really well,for rust.reassemble. Still runs hot but it is better. So I order new radiators off ( big online website) 90 bones for 2 really nice aluminum radiators. Now after a hour ride 1/4 gauge, instead of edging the red zone. I’m very happy. Back to the shiny stuff.

[landisr]

Congrats, and thanks for the follow up.

Ron in AZ

[WingAdmin]

Good find, and glad to hear you're back running again. I wonder if someone used water in there? Or silicate coolant?

[Sassy]

Congrats on the perseverance!!
Thanks much for posting what the fix was as a lot of times we never find out.
Your posts and those of others also give us novices good ideas on where to look should we in counter similiar problems.

[Weavetron]

Final note on subject. I cut off the top of one of the radiators. I'd say the tubes were visually 80% clogged. The stuff was rock hard. The radiator looked clean otherwise, no corrosion. Thanks for all the positive feedback.

[gford]

which website did you get he new radiators from?

[Weavetron]

I used a Amazon gift card. They were the cheapest I could find. Boy was I pleased when I opened the box. They are really nice. Look like racing radiators,bolted right in. Work great. I hate to cover them up with body work.

[WingAdmin]

There are quite a few aftermarket GL1500 radiators on Amazon.