Overheating 1991

Hey there guys, just got the bike out and licensed finally. Had a bit of a headache getting running after the winter, but another cleaning of the carbs got the job done nicely. Unfortunately I seem to have developed a case of "bad thermostat" over the past several months. I rode to work today, about 45 minutes of stop-and-go commuter riding, and the temp gauge hovered around the halfway point. On my way home today traffic was much worse and I was stationary for minutes at a time. The temp gauge needle went into the red and started bouncing. Once I was able to get moving (very shortly after entering red) the temps cooled down, but still were in the upper half of the gauge. Ambient temps were probably in the upper 50's this morning and low 80's on the way home.

As I said, I'm thinking bad thermostat or thermosensor. What say you?

 

It shouldn't be overheating in all given those temps (central Ohio?). I would look to see:

Radiator full
Cap installed correctly. It's a half turn, push down and then another quarter turn
Then t-stat

Vfrs don't run that hot in the ambient and conditions you describe.

 

My bet is 1/2 full rad

 

Hmm...I just double checked to be sure and it's full. The overflow bottle is empty now, which it wasn't earlier. I have never done a coolant flush on this bike, may be a good time to do that before I go spending money on parts again.

Good guess on central Ohio, I'm in the Cincinnati area.

 

Ok its your cap then. Half turn. Push Down. Quarter turn more. Like a pill bottle in reverse.

 

I think we may have a winner with the radiator cap. I'll report back with my findings after tomorrow's ride. Thanks for the assist!

 

This is the second of the week. The double action rad cap is a gotcha.

Always assume something simple afflicts gen3s, they are well designed and bulletproof

The only weak spot is the r/r which I have avoided for 19 years via use if a battery tender

Report back, let us know

 

The other weak point is the thermoswitch, a very common failure, and if it doesn't switch on the fan, overheating in traffic is what you can expect.

Manual toggle switch means positive control of the fan.

 

Could also have some air trapped in the system. Make sure to "burp" the radiator especially if you decide to flush the system.

Rollin

 

At what point should the fan kick on given a properly running system? So far as I know, mine never has...

"Burping the system" just consists of removing the lid on the auxiliary bottle and starting the bike a few times, adding coolant as needed, correct?

 

Check the FAN fuse/its simple enough and you can do it with a test light or you can physically remove it and inspect it. I had a blown one on my 91 about eleven years ago when I moved to sunny florida from rotten NJ. I dont know how long it was blown but I was sitting for a minute or two waiting for a bridge to go up and all of a sudden I had anti-freeze pissing out of the over flow. I was able to get home with no over heating issues and checked the fuse and sure enough it was blown.

No issues since. Idle the bike or take it for a spirited ride and see if the fan comes on. Could put power to the fan plug with an external power source too I guess. Different ways to skin a pussy, err I mean Cat. Its a good bike with a couple of hick-ups here and there. I plan on hitting the 100,000 mile mark on mine, gots 76,000 now. Cheers.

 

I burped with both caps off and bike running (not super hot) until it you can take it off the choke. Usually about 5 mins tops. then refill/top up and replace caps

you want to make sure the thermostat opens to release any air anywhere in the system

fan usually comes on around 165-180 degrees F

 

I agree with others, if you haven't flushed your coolant it would be a good time to do it. Make sure that the new coolant you use does not have silicates in it. I have found that it doesn't take that many years for the coolant to start looking cloudy.

If you need to just top up you can add it to the overflow bottle, The system will siphon it into the radiator as needed. You generally don't need to Burp anywhere as the overflow line is at the highest point in the system. Air is sent into the bottle where it goes back into the air and fluid is sucked back into the radiator as the engine cools back down, the trick is to keep coolant in the bottle.

You fan should be coming on as the engine gets hot.

 

safe to assume you've fitted a toggle switch for your fan then?

Is it an easy mod? sounds like a fine idea. I've always been slightly unsure of my thermoswitch. My '91 runs cool as you like on the move, but quickly gets hot in stop 'n start traffic.

 

Beta is the MAN when it comes to those rad caps! To anyone else that reads this thread, if Beta says its the rad cap, don't fucking question him! :wink:

 

Lolz!!!!!

Too funny

 

While beta is indeed the man, I don't think that the cap is the whole solution in this case. The bike did run cooler on the way in this morning (45 minute ride, stop and go through suburbia including some minutes of idling in traffic; ambient temps in the low 70's) but still exceeded the halfway mark on the temp gauge if I wasn't moving, but never got up to the redline. We'll see how it does on the way home with temps in the mid 80's. I paid attention to my fan - it isn't coming on at all, no matter the temperature.

So, initial thoughts:
1.) The thermoswitch is not activating the fan.
a.) Install a bypass circuit and toggle switch -OR-
b.) replace with new working part
2.) The thermostat does not appear to be allowing proper coolant circulation through the system
a.) Keep running for a bit longer and see if it loosens back up (I don't recall this issue before putting it up for the winter) -OR-
b.) replace with new working part

Your thoughts?

 

in general they run 2/3 of the non red part of the dial and on really hot days go up to 3/4 to the "redline", so I think your cooling is working

the fan not coming on isnt helping, have you tried a hotwire solution to determine if the fan works? if it does, many guys have wired in a toggle switch to control the fan, it's a cheap solution and you can label it "NITROUS" and pretend you are cool n sheet

 

We used to call those "New York City Switches". What he said above, get a twelve volt battery source, old mc battery and get some alligator clips that go to the terminals of the battey and then un-plug your fan switchie and give it energy. Other methods you could use could be a test light or a mutli meter. You just need so see if the switch is getting power. The official Honda manual is an excellent thing to have and I do recall a test for the thermal switch in it as I was trouble shooting an electrical bastard thingie yesterday on Old Faithful.

My view point on the switch is this, If those Japanes engineers thought we needed something like that, they woulda engineered it into our bikes. The other side of the street is this, Well if the bike does heat up to that point, its too late by the time the fan comes on, by bypassing the circuitry and making the fan come on early, you have a cooler running bike. Dont really know who is right. I rode in NYC a bunch of times and never had an issue, and I hate hacking into bikes electrics anyway, but thats just me :smile:

 

here is the shop manual if you dont have one
Download VFR 750F Shop Manual.pdf from Sendspace.com - send big files the easy way