GL1500 (1988) Overheating issue (Yes the fans come on)

[GaryBGL1500]

Hi all,

I picked up a 1988 GL1500 a few days ago and it's utterly wonderful. First time GL1500 owner (But long time bike owner. I still have a few track bikes and an S1000R).

I've ridden it a few times now and on a run the temp gauge sits solidly in the middle of the dial. At idle for a long time or in stop-start traffic the gauge creeps up towards the red (and would get into the red if I let it).

Both fans kick in but they don't seem to bring the temp down as quickly as I'd expect and will go on and off even though the temp sits high. I'd expect them to come on at a set point and not go off until the temp gauge displayed is "normal". I have checked the coolant level in the reservoir with the dipstick. I've also had the rad cap off and checked the level in there and both seem fine.

What should I be checking next? I don't like randomly replacing parts/throwing money at a problem and would like some help on diagnosing the cause.

The next thing I'm going to check is for any possible air locks and run it up to temp with the rad cap off from cold to see if that'll "burp" the system but after that I'm a bit stumped.

Thanks in advance all and there's some great info on here.

[GaryBGL1500]

I've taken the wire off the fan switch and grounded it out to confirm the fans come on and they do. I'll wire a manual fan switch in for now so I can manually switch the fans on and leave them running to confirm that if properly on that they bring the temp down as it should.

I have also tried burping the cooling system and a lot of air did seem to come out but even after that, the fans still come on but don't stay on for long enough to bring the temp back down.

I suspect I have a faulty fan switch that hasn't "failed" completely but is doing weird things. I guess the manual switch would confirm that?

[GaryBGL1500]

OK next update...

I've wired the fans to be permanently on and I can still get the bike to overheat when sat still.

I brought it up to temp (Just past centre of gauge) and then switched the fans on manually. I left it idling for about 10 mins and the temp still increases (albeit slowly) but just continues to rise.

[4given]

Read “GL1500 overheats at an idle” on this forum

[4given]

By Weavetron. I hope you find a solution before you get to his fix.

[GaryBGL1500]

By Weavetron. I hope you find a solution before you get to his fix.

Thanks very much. Just had a read of that and sounds very similar to the problem I'm having.

I'll try a rad/coolant flush first before I resort to ordering new rads. For now I've wired in a fan switch so that'll keep em on and buy me more time in traffic.

Ebay seem to list some aftermarket Alloy ones for £150 so worst case it won't break the bank.

[WingsandThings]

My bike used to overheat when sitting when I first got it. I flushed the rad and put in new coolant and it solved the problem. I think there was air trapped somewhere in the system.

I followed the steps outlined here in this thread
viewtopic.php?f=14&t=31083

[MikeB]

Flushing the radiators is a really good idea. You could also try cleaning the radiator fins. Over time, the fins get clogged and do not allow proper air flow to allow cooling.

My '98 has a little over 200K miles and the temperature hovers in the middle of the range when it is hot (80f/27c and above) otherwise it is only at 1/4 scale. Mine has not had a heating problem. The temp always comes down. But I think I may be tempting fate. I plan to douse it heavily with hydrogen peroxide or HVAC Condenser Coil Cleaner. I am sure it needs it. The peroxide will help dissolve the bugs that have been caught in the fins.

[GaryBGL1500]

Well, repeated flushings of the rad have got a lot of crap out and its definitely improved things. I'll take the fan switch out and keep flushing through and see what else I can shift from inside there. Certainly a lot of limescale type deposits.

Thanks for the advice chaps.