Thermostat question

[dwalby]

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

I've always assumed it was the opposite problem, the unimpeded flow causes the coolant to go through the radiator too fast and not enough heat is removed.

In your scenario, since the temp gauge measures the coolant temp, if it stays cool all the time what's the symptom to know the engine is overheated?

 

[red one]

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)....

It depends. If it's a cold or cool day it will take longer. If it's like 90F degree's it will be pretty quick. The temp guage and thermostat will act diffrently than if installed on a big car engine....due to radiator size? so don't compare the two. On mine once I start it and get ready to ride it about 2 miles is when its at quarter guage. Mine will stumble a bit till the guage is at one fourth range after that is smooth.

 

[Bush]

In your scenario, since the temp gauge measures the coolant temp, if it stays cool all the time what's the symptom to know the engine is overheated?

Exactly. Larry's thought makes no sense at all. An engine with a stuck open, or no thermostat at all, will always run cold.

Unless maybe you are riding around in Death Valley all day.

 

[Andrew Shadow]

An engine with a stuck open, or no thermostat at all, will always run cold.

It will run cooler as long as there is sufficient air flow through the radiator to keep it cool. With most vehicles, there isn't sufficient air flow to deal with a stuck open thermostat when they are not moving. They may not overheat, but they will get hot.

Cool engine temperature when moving and high engine temperature when stopped are symptoms of a thermostat that is stuck open. Even on older cars, where the radiator fan ran all of the time, when the vehicle is stopped or moving very slowly the temperature will begin to climb as the temperature of all of the coolant rises simultaneously. This is because it never stays in the radiator long enough to dissipate enough heat to keep the engine at the normal operating temperature. As soon as the vehicle begins moving more quickly again and air flow through the radiator is increased to compensate for the short amount of time that the coolant is in the radiator, the temperature drops back down again.

 

[dwalby]

Cool engine temperature when moving and high engine temperature when stopped are symptoms of a thermostat that is stuck open.

and also the symptoms of a normally operating ST1100, depending on your definition of 'high'.

 

[Rogue_Bolo]

Follow-up,
I ordered a "genuine" Honda T-stat on eBay from a dealer in Seattle, Washington. After removing the Tupperware in 90°F (32°C) heat on a residential street(major ordeal for these old bones), I gave the old rig another start to give it another look with fresh eyes. I figured on another common cause/easy fix is the fan switch. Unfortunately, the switch is not stocked by dealers in the Chicagoland area, so once again I ordered the part from the Seattle dealer on eBay. For a heads up I discovered the overflow line at the Radiator cap housing was corroded shut. That issue was easily dealt with using a small drill bit to punch through the corrosion. I also found another issue common with this model rig, leaky vacuum fuel valve. For now I will probably bypass the valve. I will keep the forum apprised of my ongoing adventure. thx all to date.

 

[Rogue_Bolo]

and also the symptoms of a normally operating ST1100, depending on your definition of 'high'.

It's been my experience with older cars that I worked on that engines run cold/take forever to warm up sans T-stat.

 

[Erdoc48]

Just want to interject what happened to me a few months ago- at a traffic light (a long one), my 94 temp gauge started to head for the higher end (which it never does)- alarmed me and what I did first is assume the fan wasn’t going on (it wasn’t)- I took off the left side panel and cleaned the fuse contacts and my fuses (some had some oxidation in gray black)- cleaned them with fiberglass pen (for bodywork prep), reinstalled the fuse and the fan worked again. I then bought the appropriate fuses and just switched them all out being near 30 years old. No issues since then.

 

[Andrew Shadow]

and also the symptoms of a normally operating ST1100, depending on your definition of 'high'.

Out of the usual operating temperature range that is normally the condition for the vehicle in question.

 

[Rogue_Bolo]

Just want to interject what happened to me a few months ago- at a traffic light (a long one), my 94 temp gauge started to head for the higher end (which it never does)- alarmed me and what I did first is assume the fan wasn’t going on (it wasn’t)- I took off the left side panel and cleaned the fuse contacts and my fuses (some had some oxidation in gray black)- cleaned them with fiberglass pen (for bodywork prep), reinstalled the fuse and the fan worked again. I then bought the appropriate fuses and just switched them all out being near 30 years old. No issues since then.

That's sound Advice, Thx. I did take a look at the fuse for the fan seen some corrosion on the contacts. I don't think I will go as far as replacing all the fuses, but I will probably clean all the fuses and apply some electrical grease to deal with the corrosion.

 

[Rogue_Bolo]

Update,
Replaced the Fan switch located on the radiator. Fan is working, Bike is still running hot but is ridable now. guess I have to change the Thermostat afterall.

 

[red one]

Update,
Replaced the Fan switch located on the radiator. Fan is working, Bike is still running hot but is ridable now. guess I have to change the Thermostat afterall.

If you have not done it now is the time to do a coolant service on your bike. Thermostat coolant overflow hose and cap. You already did fan switch so after you do your service you will have replaced everything in the coolant circuit except for the radiator. Btw don't forget to clean the bugs off the radiator.

 

[Rogue_Bolo]

If you have not done it now is the time to do a coolant service on your bike. Thermostat coolant overflow hose and cap. You already did fan switch so after you do your service you will have replaced everything in the coolant circuit except for the radiator. Btw don't forget to clean the bugs off the radiator.

Thx for the heads up.
I flushed the cooling system before I covered him for the winter. The only Matter I have left is the T-stat. I recently bought an OEM on eBay from a dealer in Seattle. Took the rig for a couple of short hops around the neighborhood. Bike runs hot but is not overheating and fan is turning on, but near the overheating red mark. The overflow line at the cap was corroded closed. I dealt with that using a small drill bit.

 

[Larry Fine]

Exactly. Larry's thought makes no sense at all. An engine with a stuck open, or no thermostat at all, will always run cold.

I completely agree that the coolant will run colder than it should with no restriction. I'm suggesting that the engine metal, not the coolant, can overheat if the coolant doesn't remain in contact with it long enough to absorb heat.

Of course, variables come into play: how hard you're running the engine, air temperature, air flow through the radiator, relative contact areas of engine and radiator, coolant flow speed, etc.

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https://www.garagejournal.com/forum/threads/overheat-without-thermostat.32411/