Thermostat question

[Rogue_Bolo]

Greetings all,
I'm about to purchase an automotive thermostat as a substitution for my defective stat (overheating issues). I'm going to go with the ones suggested on an earlier forum post from a Honda Civic. Is the bypass hole on the stat necessary?

 

[Roger]

Always! Or the thermostat would not be able to pass any water and therefore stay cold......

 

[Rogue_Bolo]

Always! Or the thermostat would not be able to pass any water and therefore stay cold......

Thx for your answer. If a bypass hole is needed for a bike, then why is said hole not part of an Automotive stat? What is the difference in the operation of a stat for a bike vs a car? Really curious about this one as I lack the facilities to drill a hole currently. Just like to know so I can budget for a Dremel tool.

 

[Roger]

Never seen a thermostat without a bypass and a little 'jiggler' in to keep it clear....

 

[Rogue_Bolo]

Never seen a thermostat without a bypass and a little 'jiggler' in to keep it clear....

I have to admit that it has been sometime since I performed a thermostat change. Maybe this is something I never really noticed for when I performed a change on my previous cars, the existence of bypass hold and orientation wan never a factor (considering that the vehicles in question were products of the '70s and '80s (with a '69 Plymouth Fury, and a '53 Chrysler thrown in for good measure)

 

[Larry Fine]

Think about how a T-stat works: it only lets hot coolant leave the engine.

For that to happen, the hot water has to be able to reach the T-stat.

In my opinion, however, the hole makes filling a cool engine go faster.

 

[bdalameda]

Yes the hole is to allow the system to be bled easier. It gives a place to vent and also air to escape.

 

[Bush]

Buying a Dremel to cut a hole in the cheaper Civic thermo hardly seems economical.

Have you ascertained that it actually is a stuck closed, or not fully opening thermostat, that is causing your overheating problem? Lots of other reasons for overheating besides the thermostat.

 

[Art Franz]

in my experience thermostats VERY SELDOM go bad. (I owned an automotive cooling system shop for several years) Its almost always something else thats gone wrong. the biggest problem Ive encountered with thermostats is when a strip of RTV gets caught in them, causing them to stay partially open. and yes, the bypass hole is necessary, for reasons already mentioned above. best way to check if it is bad or not, submerge it in water on your stove. It will be fully closed at room temp and should be fully open by the time the water is at a rolling boil. and not start to open until the water reaches 195 degF, which will be shortly before the water reaches boiing, if youre below 3-4000 ft above sea level.

 

[Rogue_Bolo]

Bush, Art Franz:
I discovered the overheating issue on my ride home after the purchase. The bike was seldom used by the previous owners (1991 with only 14k miles on it). The overheating occurred when I was stopped while in stop and go traffic on the highway. The problem reoccurs while sitting on idle. During that time the fan has come on, but only when the temperature gauge is nearly pegged. Also while the cap was off the coolant was bubbling out when the engine warmed up. These symptoms are similar to the issues I had with my past cars and replacing the thermostat have addressed these problems in the past. in those day it was easy to diagnose a thermostat issue by looking for coolant flow in the radiator as the engine was warming up (during my youth radiators only had a drain tube with no overflow tank). I changed the coolant in preparation for the winter as I didn't know when the last time it was changed. This was when I was performing a diagnosis before winter storage. To check the thermostat in a pot of hot water I still have to remove it. as such I will be preemptive and replace it as long as I have to remove it to test it. I will still test the thermostat to determine if it is still operating properly as a means to determine if it is an issue, or if there are further matters to address.

I plan to use a Dremel as an option for drilling a bypass hole on the thermostat if needed as I live in an apartment with no off street parking, and I am limited in space (I stored my bike winterized and covered on the street). When I replaced Thermostats for my cars, I don't recall seeing a bypass hole on them and orientation was not a factor in their installation. I just like to know what is different in the operation of a thermostat for this motorcycle vs a car, especially considering that an automotive thermostat can be substituted for a motorcycle thermostat?

 

[bdalameda]

I would bet that it was not the thermostat that caused the overheating situation but more likely low coolant level in the engine and radiator - the coolant overflow hose that attaches to the top of the radiator and goes to the expansion tank on the ST1100's are known to degrade and crack. When this happens the coolant cannot be pulled back into the system as vacuum cannot develop when the engine cools down and coolant gets lost over time. When this happens the coolant level in the expansion tank appears normal but the amount of coolant in the engine and radiator is too low. This is not too noticeable as long as you are moving and keeping things cool but when you stop and the temperature climbs the system goes beyond its ability to bring the temperature down and the temperature runs away due to the low coolant level and air in the system. This is far more common on the ST1100 than thermostat failures. If I were you I would carefully inspect this hose and consider replacing it just for good measure.

 

[SMSW]

When you install your thermostat, the hole goes at 12 o'clock.

While I would never discourage anyone from buying another tool, and dremels are extremely useful, are you really saving that much money by purchasing an automotive thermostat? You don't own a set of twist drills and a drill motor? Is that humanly possible? Should you drill your hole, how will you install a little clapper (ok, @Roger. called it a jiggler) to keep it clear?

Speaking of these, it sparked a memory - an oldie but good one. Pardon my digression, this is a serious answer to you post with a pause for some amusement.

Other posts notwithstanding, I had a thermostat failure. There was sufficient coolant in the system, and the stat started sticking - it took a long time for it to open and eventually would not close. When I pulled it, there were scratches on the center 'post'. Larry said these were evidence that the stat was failing. Replacing it (though I muddied the waters by also replacing the o-ring, a few hoses, clamps and coolant) solved the problem. I say 'muddied the waters' because if you want to determine a cause of failure, you have to change only one parameter - though one could argue that its hard to describe how the o-ring could be the cause of overheating.

 

[bdalameda]

The St1300's used to have a lot of thermostat failure due to defects. The St1100 thermostats have mostly been trouble free.

 

[red one]

Greetings all,
I'm about to purchase an automotive thermostat as a substitution for my defective stat (overheating issues). I'm going to go with the ones suggested on an earlier forum post from a Honda Civic. Is the bypass hole on the stat necessary?

The one I bought from advanced auto had a hole already drilled in it but contained a pin called a jiggle valve. Take a pair of side cutters and cut the pin out. I did not like the way my Stant thermostat performed so I wound up ditching it and just getting an oem thermostat.

 

[ST1100Y]

The overheating occurred when I was stopped while in stop and go traffic on the highway. The problem reoccurs while sitting on idle. During that time the fan has come on, but only when the temperature gauge is nearly pegged.

Actually symptoms of low coolant level...
So I'd first check for possible leaks and ensure a full system... (which means the entire circuit, carbs off, check everything underneath there...)
Another, however rare issue, would be a corroded pump impeller (you mentioned seldom use of the bike, so who knows how long the old coolant was in there, subverting, turning corrosive...)

 

[Josh_ST]

Just a thought, I've seen several Home Depot's and Lowes stores with tethered drill demo models with wood blocks to drill in . Maybe "demo" their drill on your thermostat? Even if you have to buy a proper sized drill bit, that's cheaper than the whole tool!

 

[dwalby]

I'm going to throw in one more vote to make sure the cooling system is completely filled (at the rad cap, not the overflow tank) and see if that cures the problem. Also, when I replaced my t-stat with an automotive type it had the hole and jiggle pin so I doubt there's going to be any drilling required.

FWIW, there was nothing wrong with my t-stat, but since I was re-doing the upper hoses and had the t-stat housing off the bike anyway, I figured why not replace it since it was close to 20 years old.

 

[diferg]

Funny, almost related story: I had an ancient SEAT 850 and, (in my wisdom, to prevent overheating?) I removed the thermostat. With no thermostat the engine would quickly overheat! Replaced thermostat and no more overheating. Leson Learned for me.
Fast forward 18 years. My ST 1300 thermostat stuck open and engine ran cold. Replaced thermostat and all was good again! There must be "magic smoke" in thermostats. LOL

 

[Roger]

Just a question - how many km/miles are required for the engine to reach 'normal' working temperature....? Mine takes up to 5 miles of unimpeded running to reach the 1/4 mark starting from outdoor cold (not from a warm garage)....

 

[Larry Fine]

With no thermostat the engine would quickly overheat! Replaced thermostat and no more overheating.

Think about how a T-stat works: it only lets hot coolant leave the engine.

If the coolant doesn't stay in the engine long enough to absorb heat, it can remain cool while the engine overheats.