Thermostat Replacement

I'm having what I think is the opposite problem, my thermostat may be stuck closed. The bike, and '85 VF500F starts and runs fine, but once warmed up sufficiently I get a leak at one of the cooling pipe connections. Once while stopped at a light the temp gauge started to rise. Once cool and I check the coolant level in the radiator, it's full to the top in spite of the leak.

I installed a new thermostat in the spring and replaced all gaskets in the cooling system. I had one leak also at a cooling pipe connection. Fixed that, but now it leaks on the other side. My thermostat is easy to access, so I think I'm going to remove and test it and either put the old one back in, or get another new one.

What do you think?

 

Any leak, significant enough to allow a pressure loss will cause the bike to overheat. My thinking is that your thermostat is fine but you have a pressure leak in your system. A stuck thermostat will cause the temperature to skyrocket in short order and will blow hoses off.

 

So then I should fix the leak I have and see it operates.The temp only went up once while at a light, not by much, and then returned to normal once going again.

 

I had an 85 VF500F like yours. I do not remember the temperature climbing but it really does on my 5th gen. If you have a leak by all means, fix that first.

 

You can do a basic "does it work?" test on the thermostat function with it installed on the bike, starting with a cold engine. If everything is working normally, the thermostat will stay closed until the coolant reaches operating temperature, which means the coolant stays within the engine/pump circuit, so the radiator will stay cold. Once operating temperature is reached, the thermostat will open and the now hot coolant will start to pass through the radiator, which will suddenly get pretty hot.

So start your engine and let it warm up, and put your hand on the radiator every now and then. If the radiator gradually warms up, the thermostat is stuck open. If the radiator stays cold for a while, then quickly gets too hot to touch, the thermostat is probably fine. If the radiator never gets too hot to touch, then your thermostat is probably stuck closed.

To be honest, your description just sounds like a loose hose clamp that lets a little coolant out when the system gets hot and pressurises. When the system cools off it will draw back from the reservoir, so I'd expect to see that dropping over time. It is very normal for a motorcycle to get hot when stationary as there is no airflow through the radiator, until such time as the temperature is high enough to trip the switch that runs the fan.

 

When I first got my VF500F. it had been sitting for a long time. When I first started it up is leaked water from every pipe and hose. The Honda service tech said to run it and get it hot a couple of times and see if it seals up. It did. I am with Cadbury. Check your hose clamps and do the "does it work" test.

 

Nice photos, i wish replacement cure the problem. Good write up it would help us me too because past few days i am facing the same problem with my bike.. seriously you are the savior.

 

I have a 2005 VFR800. Anybody know where is the ECT sensor and what it looks like? I tried to look for the part number but cannot find it. My Fi light blinks 7 times and indicated I have ECT sensor error code. Thanks guys

 

Can you explain to me how the ECT sensor on my 2005 VFR800 works? If that fails, what happen? My Fi error code blinks 7 times and that indicates ECT sensor problem

 

This is a great and helpful thread. Unfortunately, it's needed. "Engineers" that design things like this should be jailed for a minimum of 10 years. This kind of "design" goes against the laws of nature.....similar to child molesting.

Something else that pisses me off is that my local Honda dealer has a shop rate significantly higher than my local Honda car dealer. Go figure. Honda makes great cars too. They don't break. At least mine hasn't.

 

You are not wrong but just for argument sake I am going to play "devils advocate." Engineers are often hampered by bean counters. They are driven by forces of design but also by "cost per unit." I am sure the thermostat in the block solution saved a few yen. As for the Honda dealer shop rate I think it might have to do with volume. A Honda bike dealer doesn't do nearly the volume of work that a car dealer does.

I am more pissed that Honda built this thermostat solution and then proceeded to install a poor quality thermostat in that inaccessible position. It's also like the cost savings in the charging system. They could have made a bullet proof charging system buy building in the changes that we all have to make and it would have added a couple of dollars per unit but saved everyone huge headaches.

 

Nice write up! Along with pictures! My 91/93 have those same thoughtful holes in the frame, mine aid adjusting the mixtures screws (needle-jets) anyway, if you have a maual the want the hole in thr t-stat to face 9 oclock as your looking at it, another words sidewas. Don't know if it matters or not. When i did these jobs i replaced all the old hoses with Samco from the good old UK. The 93 i already dod the t-stat so being that the bike was such a low milage unit and they felt good. I left them alone, rest of the kit is a nice blue, got an entire black one on my 91. eace:

 

Could anyone tell me if the sensor in the red circle in the picture is the ECT sensor for 2005 VFR800?

 

I don't disagree. Strange thing is, Honda cars just hardly ever break and are known for lasting forever. I have one and it just goes and does what it was designed to do. I would feel better about motorcycle hourly shop rates if they paid their techs money. They starve to death and usually aren't as qualified as a good independent shop.

 

So much easier on my gen3 carbureted bike. Remove the tank, easy, remove the carbs, easy, remove the rh coil, easy, open up the thermostat housing, replace the thermostat and perhaps the two small hoses while your at it, and then button it back up. Its about a one hour job at most.

 

Next time use some silicone grease on the rubber boots. Makes re-assembly and subsequent disassembly way easier.

 

What kind of RTV do you use? I typically will use a very small amount of silicon grease on tht hoses but you need to be careful not to use too much. As a matter of fact I will typically wipe tht fittings off before assembly. Otherwise you have to overtightened the clamp on the hose which will cut into the hose and cause premature failure.

 

Can't disagree. A GOOD engineer will engineer something easy to work on....like my Tacoma.

 

I just replaced the thermostat on my '92 VFR750F. There are two small hoses that go from the thermostat housing to the front and rear cylinders. I like to keep the hoses fresh but these hoses are 18mm inside diameter and the local shops only carry 5/8" (16mm) or 3/4 (19 mm). I ended up having to order a full meter of 18 mm hose. Including shipping it cost me over $32 and all i needed was about six inches. If anybody out there needs some 18mm id coolant hose just let me know and I will sell it at my cost plus shipping. Approximately $0.83 per inch. Let me know.
Mark

 

Even easier on gens 1 & 2 as thermostat housing is outside the frame, ten minute job !