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My gauge has been reading 185 while driving so I thought everything was fine. Car didn't sound right. Popped the hood. Crack in the bypass hose! I let the motor cool down and topped up the rad.....down 4 litres! $#%&%$! gauge. Lucky I didn't cook the motor. I've always taken it for granted that these gauges were reliable...then again they are 50 years old. I might consider an aftermarket unit for below the dash. Anyone else get fooled by their temp gauge?
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TR2/3/3A Reliability of TR3 Temp Gauge?
- Thread starter karls59tr
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I suspect that part of the "problem" was that the sender for your gauge was no longer in direct contact with coolant due to the loss of same through the bypass hose. I used to have a more serious version of that problem with a Saab 99: when the coolant level dropped, the electric fan sender would not get "hot" enough to trigger the fan (obviously compounding the problem)!
Now that your cooling system is again leak-free (hopefully!), give that poor old Jaeger gauge one more chance! :wink:
Now that your cooling system is again leak-free (hopefully!), give that poor old Jaeger gauge one more chance! :wink:
Don Elliott
Obi Wan
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I agree
TR3driver
Great Pumpkin - R.I.P
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I've certainly seen that happen on other cars, but never with the TR3. In fact, I popped a bypass hose just the other day, and the gauge dutifully climbed for the sky once the coolant got too low to circulate.
My theory is that you caught it just in time, and the coolant wasn't actually overheated.
Of course, although it's not common, it is possible for the gauge to fail such that it will only climb so high. It might be worth testing it in some fashion, to make sure it still works. If you just put some plain water in an old soup can, and heat it to boiling, that's pretty close to 212F/100C.
My theory is that you caught it just in time, and the coolant wasn't actually overheated.
Of course, although it's not common, it is possible for the gauge to fail such that it will only climb so high. It might be worth testing it in some fashion, to make sure it still works. If you just put some plain water in an old soup can, and heat it to boiling, that's pretty close to 212F/100C.
I'll test the gauge just to make sure it's functioning. Anyone know if there is an "L" shaped hose from another vehicle that would work instead of ordering from the big three and having the car sit while waiting. I wrapped the old one in plumber's high pressure tape. Maybe that's as good as it gets for a temporary fix?
prb51
Luke Skywalker
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my original style gauge is off about 18 degrees. Always records low in that manner but does so continuously so I know what temp I'm at. The thermostat always opens at the same point and I pulled the bulb to measure the gauge against another temp device in heated water. Consistantly 18 deg low.
This happened shortly after a new rebuild on the unit and has remained consistant for a few years.
This happened shortly after a new rebuild on the unit and has remained consistant for a few years.
Geo Hahn
Yoda
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My gauge is pretty accurate (checked with a IR thermo).
I always have a spare bypass hose though you may get by with a length of heater hose. Even a kink in it won't matter much (many have that hose mostly blocked anyway).
Apparently ypu don't have the safety feature I have -- when my bypass hose split it promptly drowned the #2 plug and the miss told me something was, well, amiss.
I always have a spare bypass hose though you may get by with a length of heater hose. Even a kink in it won't matter much (many have that hose mostly blocked anyway).
Apparently ypu don't have the safety feature I have -- when my bypass hose split it promptly drowned the #2 plug and the miss told me something was, well, amiss.
I tested the gauge by immersing the sender tube in boiling water. It registered 212F so the gauge is functioning. It appears as if when there was no coolant around the sender because of the bypass leak then the gauge did not register the higher temp but stayed at 185! It follows that I was driving around with the coolant down 4 litres!!! and the gauge not telling me there was a problem. Shouldn't the gauge have indicated a much higher temp? What about installing an aftermarket sender in the bottom rad hose???that way the sender would be immersed in hot coolant from an overheating motor and the gauge would warn me of the problem. Or am I missing something here?
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I don't think that will work; coolant flow is (assuming the thermostat is open) from the bottom of the radiator to the water pump, then to the block, up through the cylinder head and (open thermostat) to the top of the radiator. So the upper part is where the water is hottest, and that includes the area where the sender is located. I still stand by my guess that no sender will read as accurately in air as it will in coolant. :wink: That said, I just don't think you'll get as accurate a reading from the bottom of the radiator...but I could be wrong!?
Geo Hahn
Yoda
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Well it is a potential problem but I agree with Andy that the temp at the bottom of the rad won't tell you much -- might even not tell you that you were down a gallon as at that point coolant wasn't circulating normally and the big heat would have up at the head.
A local club member cooked the engine in his XK150 climbing up to Jerome, AZ a few months back -- had lost a bunch of coolant and, as noted, those senders (capillary or electric) don't work worth a darn measuring air temp. First indication of trouble was a seized engine.
Check the coolant often and be on the look-out for anything unusual.
A local club member cooked the engine in his XK150 climbing up to Jerome, AZ a few months back -- had lost a bunch of coolant and, as noted, those senders (capillary or electric) don't work worth a darn measuring air temp. First indication of trouble was a seized engine.
Check the coolant often and be on the look-out for anything unusual.
jdubois
Jedi Warrior
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Andrew Mace said:
Accurate is sort of a philosophical question since the temperature is not constant throughout the cooling system, but the top of the radiator should (assuming you've got the correct amount of coolant flowing) obviously always give you a higher temperature reading than the bottom... or you better buy yourself a new radiator!
TR3driver
Great Pumpkin - R.I.P
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One way around this might be to fit a cylinder head temperature sensor. It should show the excess heat if the cooling system has failed or there is a big pocket of air. I recall Dad had a Buick wagon with a big "STOP" light on the dash, to tell you that you had failed to work all the air bubbles out of the cooling system.
Still, I've never had any problem with the stock sender location on a TR. If there is any coolant at all left in the engine, it will boil and blow live steam past the sender. And if you don't notice until there is no coolant left at all, the engine is likely toast anyway. Might as well keep driving it until it seizes.
Oddly enough, I just went through Geo's scenario a few hours ago ... bypass hose failed and sprayed coolant all over the ignition. Even if I hadn't noticed the spray onto the windshield, the ignition cutting out would have been an unmistakable indication something was wrong!
Still, I've never had any problem with the stock sender location on a TR. If there is any coolant at all left in the engine, it will boil and blow live steam past the sender. And if you don't notice until there is no coolant left at all, the engine is likely toast anyway. Might as well keep driving it until it seizes.
Oddly enough, I just went through Geo's scenario a few hours ago ... bypass hose failed and sprayed coolant all over the ignition. Even if I hadn't noticed the spray onto the windshield, the ignition cutting out would have been an unmistakable indication something was wrong!
MGTF1250Dave
Jedi Knight
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Aloha,
This is when we need Dr Entropy. It has been awhile since I studied thermodynamics, but water in a non pressurized system at sea level will boil at 212 degrees F and never get hotter, regardless of the amount of heat applied. Altitude and anti-freeze will change that temperature somewhat, altitude lowering the boiling point and anti-freeze raising it. So with the ruptured by pass hose, the cooling system was not pressurized and the cooling fluid would never become hotter than its boiling point. Ambient air temperature would reduce the temperature of any steam or vapor in the thermostat housing so the 185 degree F temperature I believe was fairly correct at sending unit.
If you use a water and anti-freeze mixture as coolant, I think the best sensor to detect coolant loss is your sense of smell.
This is when we need Dr Entropy. It has been awhile since I studied thermodynamics, but water in a non pressurized system at sea level will boil at 212 degrees F and never get hotter, regardless of the amount of heat applied. Altitude and anti-freeze will change that temperature somewhat, altitude lowering the boiling point and anti-freeze raising it. So with the ruptured by pass hose, the cooling system was not pressurized and the cooling fluid would never become hotter than its boiling point. Ambient air temperature would reduce the temperature of any steam or vapor in the thermostat housing so the 185 degree F temperature I believe was fairly correct at sending unit.
If you use a water and anti-freeze mixture as coolant, I think the best sensor to detect coolant loss is your sense of smell.
TR3driver
Great Pumpkin - R.I.P
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Even at 10,000 feet above sea level, water still boils at 194F. And given the amount of energy it takes to liquefy steam, I seriously doubt that the steam is cooled to any extent while passing through the thermostat housing.
Besides, who runs pure water? Even 30% glycol will raise the boiling point signficantly.
At any rate, with my unintentional experiment with a failed bypass hose just this morning, my temp gauge had no trouble reaching 230F!
Besides, who runs pure water? Even 30% glycol will raise the boiling point signficantly.
At any rate, with my unintentional experiment with a failed bypass hose just this morning, my temp gauge had no trouble reaching 230F!
MGTF1250Dave
Jedi Knight
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Thanks for the data from your tables Randall. I agree that the most significant factor affecting the boiling point of the coolant is the anti-freeze. So with a one third anti-freeze and two thirds water mix, the coolant and any steam would never exceed 220F with a ruptured hose. I perhaps over estimated the cooling effect of air flow over the thermostat housing where the sending unit is located.
As your experiment showed, the oily mist on the wind screen and the tell tale odor of hot anti-freeze is a reliable coolant loss detector.
As your experiment showed, the oily mist on the wind screen and the tell tale odor of hot anti-freeze is a reliable coolant loss detector.