New Thermostat Stuck Open?

[VicSev93]

Hey all!

First off, I wanted to thank you all with a post I had a while back about a coolant leak. It was in fact in the V of the bike. (1998 Gen 5 VFR) so I got to work. Changed out the hoses and also the thermostat. New coolant of course.

Now I have another issue. My bike is slow to warm up. I believe my new (OEM thermostat from Partzilla) is stuck open. Bike is very slow to warm up to operating temp. (168-172F) I read somewhere on forums the way to check if its open is feel the rads. If they get hotter as the bike warms up to operating temp then it is stuck open. If they are cold and suddenly get hot around operating temp then I'm good to go.

Problem is, they are already warm by the time my bike is 124F. Did I miss something? Do I need to burp the air from coolant? If so, how would I go about doing this?

Thank you.

Pic of the bike for attention. 😂

[Steampunk]

I purchased a '98 last November and over winter went through the bike.  Not sure why, but the previous owner had just changed coolant (I suspect the bike was dropped and a new radiator installed on that side).  After the test ride (really cold, late November in Colorado) the bike spit a bit of coolant out the overflow.  Okay...  Then, after going through the bike over the winter, I started the bike with fairings off and it spit some coolant again.  Read the service manual and it said to fill the radiator and overflow tank, start the bike , and after it warmed up, to blip the throttle hard a couple times.  After it cooled down, I checked the radiator level and it had dropped.  I topped off the radiator, and did the procedure again.  After it cooled, I checked the level and it was down just a wee bit.  I topped it off and took the bike for its first short ride without the fairings on.  It dropped a quarter-sized spot on the floor after the ride.  I put the fairings back on and rode the next day about 150 miles, watching for signs of trouble all the while.  It spit a nickel-sized spot of coolant from the overflow after I parked it in the garage and that has been it.  No more coolant pukes.  The bike runs at proper temps and the levels are good.  So, this is a long-winded way of saying I think you're onto something with the air being trapped.  Check the coolant in the radiator and the overflow tank, and top off if necessary.  Do the throttle whacks once warm, and recheck.  Then a good ride with some rpms raised a few times.  As an aside, when I install a new thermostat or am suspicious of a used one, I put them in a pot of water and boil.  This will verify that the stat is opening, and as deep in there as the stats are on VFRs, it's time well spent.  Best of luck, and let us know the outcome.  Cheers. 

[Bren]

When you burp the cooling system it has to be done on the sidestand with the rad cap off, rag at the ready in case of coolant eruption. Best is to position the bike so the rad  cap or filler neck is at the highest position. Use an incline to do it.

With the cap off and up to temp you should see the coolant moving/flowing down through the filler neck.

Doing high revs on the highway won't release the air as the cap is on and the system already pressurised = no means for air to escape.

 

If the thermostat is working properly then the left rad gets warmer before the right rad on start up.

[Skids]

An alternative or addition to the above burping was passed to me many moons ago: get a friend to help, coolant cap off, sidestand up and in gear, lean the bike over to the left as far as you can manage (peg scraping if poss). You should notice some burping and when you pick the bike up again, you'll notice the level in the rad has gone down slightly. Top up, maybe repeat, up to you. I've used this method several times as well as the throttle burp and it does seem to work.

 

YMMV.

[adkfinn]

using throttle to burp on the center/side stand with the cap off worked for me.

 

with respect to the thermostat - factory tstat begins opening at 176 degrees F. With the bike running, when the temp gauge reaches that figure, it should allow coolant to flow to the radiators. At that point (not before) you should feel a meaningful change in the rad temps ( I want to say that the right radiator warms first also? can't recall for sure) and also you should be able to see a small drop in the temp reading on the display also (2-5 degrees) when the tstat first opens as well.

 

 

[Bren]

2 hours ago, adkfinn said:

using throttle to burp on the center/side stand with the cap off worked for me.

 

with respect to the thermostat - factory tstat begins opening at 176 degrees F. With the bike running, when the temp gauge reaches that figure, it should allow coolant to flow to the radiators. At that point (not before) you should feel a meaningful change in the rad temps ( I want to say that the right radiator warms first also? can't recall for sure) and also you should be able to see a small drop in the temp reading on the display also (2-5 degrees) when the tstat first opens as well.

 

 

I'm 99% sure it's the left rad that warms up first but I've been wrong once before 😁

Good tip that I neglected to mention, once the thermostat opens the rads temp changes quickly.