Overheating...where should I begin?

Heya. My '83 vf750f Has been overheating pretty quickly. I believe it to be a radiator related issue but I want to approach checking in the most logical fashion (i.e. first this, then that and so on).

The problem is that the bike heats up to operating temp but then does not cool down and overheats in about 10 min and the clutch starts slipping and the bike becomes a giant doorstop.

The temp gauge changes very little but the thermostat housing does become very hot. No loose connections but I think the thermostat may not be opening up properly and letting coolant flow which would be why the temp gauge is not reading as it is not getting coolant touching the sensor.

The radiator is warm to the touch but not hot like it should be for the bike to be heating up so much. This could be because the thermo may not be opening up like I think or possibly the water pump is not pumping? I see no leaks and only hear a little noise that I believe to be the cams but I'm not sure.

Touching the cylinders burns the fingers. The engine is heating up but nothing is cooling it down. I believe the issue to be a lack of coolant flow either because of the thermo not opening or because the pump is not pumping.

Once upon a time (last summer) the bike ran well enough and only overheated causing the clutch to slip terribly on very hot days. Nothing has really changed since that day (no crashes, major mods, etc).

The cap was replaced with the sabmag recommended one from autozone and seems to function just fine pulling coolant from the bottle when neccesary.

I also thought that maybe some air got into the system some how? I have yet to try and take the cap off to let bubbles escape.

Any ideas? Based on the what I have said what do you think I should start with and proceed in what order? Any other ideas? I was going to vent the system and let the bubbles out if there are any, check the thermo then check the water pump. Oh, and I checked the thermo last summer and it opened at the correct temp but maybe it failed recently as it is an old part. I am by no stretch of the imagination an expert so any help is appreciated. Well, thanks in advance.

 

Hello

Hello

The first thing I would do is take the sparks out and check them then you can see if a oil is getting into the cylinders and overheating them.Then I would take the cap of the raditor and turn on the engine if you see any bubbles in raditor while the engine is running you will have water in the cylinders.To check out the termo take it out and mesure it with ohm meter while you heat it.And have your fans been running when the bikes overheats.And one last thing on side of the water pump is a valve you will open that then take a hose from that into a bottle with water in it the hose will stay under water soo no air will get in but only get out.ok

Best regards

Gunnar

 

I second the thermostat check. The bike will do just as you say if it is stuck open. These are pretty cheap and should be fairly easy to change on the older models.

 

Same thing happened to me on my 500F cepter. Overheated while driving it on a 81F day.
My system had NO pressure in it whatsoever, and my temp gauge was reaching the 3/4 mark on the gauge, which is a big NO NO!!

But after changing out the thermostat and putting in a new Radiator cap, expelling all the air, and putting in the best radiator fluid that I could find (hondafreeze) she takes a nice long time to warm up, and with little stop and go driving, she maintains by just going a hair into the larger scale zone on the gauge.

As a side note, be careful, cause after many testimonies on the forum, many found out that it's normal for the gauge to reach the 3/4 mark before the fan turns on.
Shocking when I found out, so I highly suggest you put in a fan switch to turn the fans on early!!!

I hope this helps. Just test to see if you have flow, by taking off the radiator cap, staring her up, and when she reaches 190F, you should see some flow in the radiator like I did. It'll look like a small river flowing.

If not, problem 1, you have a bum thermostat.

If you have flow as soon as the bike starts up, you have a open thermostat!!

Cheers

LL

 

Excellent. I will give the bubbles a shot then check the thermo then whatever else. It is probably time I check the plugs again anyway so I'll do that too. Ans while I'm messing with junk I might as well put the new jets in I been meaning to (it has been running lean for a while). Thanks for the help fellas (or ladies perhaps) and if you think of anything else lemme know. I'll get around to the bike in a couple days and let you know what I find.

 

oh, and where is a good place to pick up the thermo? Anyone know a part number? The honda dealer here never has anything in stock so is there an auto store equivalent? Thanks again.

 

Part number

Hello

Try hondausa.com or bikebandit.com.

 

Alternative part#'s here:

CoolingSystem - SabMagFAQ