Thermostat bypass?

Do the 2nd gen 700s have a thermostat bypass, or does coolant not circulate through the bike when the thermostat is closed?

I flushed and replaced the coolant tonight, and noticed that it was getting pretty toasty, but the fan wasn't kicking in, making me think that the thermostat was still closed. Radiator was plenty hot to the touch (with mechanics gloves), but not the 2/3 of the way from cold to hot that the gauge was showing.

btw, I flushed the system with a 50/50 distilled water/white vinegar solution, and was surprised at how dirty that looked, compared with how clean the coolant looked as it drained out. drained the coolant, added the vinegar/water solution, and then idled the bike to warm it up, and drained it out, and ran distilled water through the radiator to flush it out a bit more.

Then filled with 100% Engine Ice. Will see tomorrow how it works when riding.

 

When the stat is closed, water/coolant will not circulate thru to the radiator. As the water temp reaches the temp of the stat, the stat opens, just like in a car. For instance, if you have a 180 degree stat, then when the water temp reaches 180, it will open. Your stat might be stuck closed. Another thing it might be is the fan relay. I think it's a relay or a sensor of soome sort. On mine there is wire that comes from the radiator and I think it goes to the fan. Check that wire to make sure it is in good condition. Hope I explained that well. If not, maybe someone can explain it better than me.

 

Remove the thermostat and see if it has a small hole in it to allow a small amount of coolant by. Aftermarkets typically have a brass rivet in that hole.

The small flow of coolant will allow the thermostat to heat up - causing the spring to contract - and open the passageway - allowing coolant to flow.

Once the coolant in the radiator gets hot enough, the fanstat on the radiator will close - completing the ground circuit to the fans - which then turn on.

When the coolant gets coooled enough, the fanstat will open back up - removing the ground to the fans - and they will stop.

You can test the thermostat by heating it in a pot of water (don't let it touch the bottom of the pan). You should see the spring contract around 180 degrees.

You can test the Fanstat the same way - don't remember what temperature it's supposed to close at though.

 

ok, two questions:

1) When the thermostat is closed, does coolant circulate through the engine only, or just not at all?

2) Is it normal to get an air pocket under the thermostat when changing the coolant, and with one, does it normally take a bit to heat up the thermostat enough to cause it to open (after which the bubble gets burped out into the coolant reservoir and all is well)?

 

See here: http://auto.howstuffworks.com/cooling-system.htm

Almost exactly how the cooling system works on our bikes.

 

skip the thermostat, wire a switch from the wire to the thermostat and ground it. that way you have control of the fan. works like a charm.

 

Incorrect. The thermostat determines if coolant is going to circulate through the radiators. I believe you meant to say "fanstat".

Wiring the fanstat to a switch and complete the fan ground circuit only masks the issue. It is much better to fix the original issue.

As far as #2 is concerned - Yes. When refilling the system, I pour in the coolant slowly to try and eliminate air bubbles/pockets.

Start the bike and wait until it is warm to the touch. Then bleed the thermostat nipple. Careful - the coolant will be very warm.

Then I ride the bike to get the coolant flowing which should clear any bubbles to the reserve bottle. Or you can idle the bike with the radiator cap off to allow bubbles to escape there. Don't idle too long as the 1st gen bikes have low oil pressure when idling.

Since you did not use an overly strong flushing fluid, I would say your fanstat is OK.

Grab a cheap infrared thermometer from Harbor Freight and see how hot the engine is really getting. Your gauge may be faulty.

 

I knew they meant fasstat vs. the thermostat. My main question had been if the coolant flows at all with a closed thermostat, or if it bypasses the radiator and heads back to the pump (the bypass route isn't obvious from the service manual diagrams, if it exists).

It's better now, still runs hot as hell, but I think that's the nature of the beast. Riding it in 40*F weather in the winter doesn't really give you a feel for how hot it can get. Riding yesterday and today in 80-90*F weather, it's clearly a HOT running engine.

At over 25-30mph, it stays about at a 1/3 of the way from cold to hot, but stopping at a light I can watch the engine slowly climb up to 2/3 of the way to hot, and then the fans kick on, and pull it back down to half-way or so. Of course, then my legs are feeling like their on fire..

The head oiling issue is a 1st-gen only one, right? 2nd gen bikes are ok?

 

Yes, the thermostat only allows a small amount of fluid to pass, so essentially, the coolant just sits inside the engine until the thermostat opens up and allows coolant to flow through the radiator.

Yes, these bikes do like to run "hot". However, your fans kicked in, and the temp went down - like it's supposed to do. Sounds like your cooling system is running correctly.

As as far as your legs getting cooked - some jeans should help isolate the heat - and when stopped, I try to stand with my leg out as far as I can to avoid the heat (which is tough to do with a 29" inseam).