Problems with my BN2 Temp Gauge reading

[Martinld123]

In recent years I have had a low water temp reading in my 1956 Healey BN2 so sent to Nisonger for rebuild. My gauge reads 160 most of time even with new 180 Thermostat with an aluminum radiator. If I get stopped at a stop light for three or more changes it goes past 190 on a hot day. When I got it back it still reads the same 160 most of time with 180 stat plus oil pressure now reads 57 instead 50 as before. Okay I guess? When I run engine my aluminum radiator gets very hot even when gauge reads only 160 so my question is why is my stat opening before it reaches 180? This is my second 180 thermostat doing the same thing so should be good. Could my rebuilt gauge be reading 20 degrees low? When moving it is very hard to get temp above 160 even on a hot day here in Florida. Thanks Marty

 

[red57]

It's easy to test the temp. gauge - just pull the sender bulb out and put it in a pan of boiling water, should read 212F when the water boils.

I also wonder if you meant the oil pressure is now 57 instead of 157? If you have 150+ psi oil pressure, you need to check the pressure relief valve.
If it reads 57 as opposed to 50 before rebuilding, I think that would just indicate a re-calibration by Nisonger.

 

[Martinld123]

It's easy to test the temp. gauge - just pull the sender bulb out and put it in a pan of boiling water, should read 212F when the water boils.

I also wonder if you meant the oil pressure is now 57 instead of 157? If you have 150+ psi oil pressure, you need to check the pressure relief valve.
If it reads 57 as opposed to 50 before rebuilding, I think that would just indicate a re-calibration by Nisonger.

Yes 57 from 50. My real question is why when gauge reads only 160 is the radiator getting very hot? I thought it would not open until it gets to 180. Thanks Marty

 

[red57]

"Very hot" could be subjective - have you tested it with an infrared thermometer? 160F is very hot to the touch and would burn you if you left your hand on it for very long. Residential hot water heaters are normally set somewhere between 120 -140F and 140 is not recommended for houses with small children because severe scalding only takes a few seconds if the water is 140F. If you are just using your hand, it may be cooler than you think and still feel hot.

 

[Bob_Spidell]

Both my BN2 and BJ8 behave similarly. On a cool day, they won't go over 160deg or so unless idling for a couple minutes. On a warm day, they cruise at 180 as you'd expect, and heat up at idle even quicker, sometimes approaching 200 or more. Others have reported similar behavior and no one has come up with an explanation. I've tried numerous thermostats, including one with a movable sleeve that covers up the bypass port when it opens.

You could get an infrared 'no-touch' thermometer to get the actual temp of the radiator:

12:1 Infrared Laser Thermometer

Amazing deals on this 12:1 Infrared Laser Thermometer at Harbor Freight. Quality tools & low prices.

www.harborfreight.com

 

[Rob Glasgow]

My BT7 reacts the same. If the outside temp is 70 - 80, the water temp while driving is about 160 -165 even with a 195 degree Thermostat. If I’m driving uphill, it may climb to 180 but cools back to 160 going level or down hill. It’s only when the outside temp is 100 does the water temp reach 190. Of course the gauge goes to 210 once you shut the engine off.

 

[Editor_Reid]

Speaking of checking gauge accuracy, I couldn't resist posting this pic (of a gauge from a BN2!) once again:

 

[Martinld123]

Both my BN2 and BJ8 behave similarly. On a cool day, they won't go over 160deg or so unless idling for a couple minutes. On a warm day, they cruise at 180 as you'd expect, and heat up at idle even quicker, sometimes approaching 200 or more. Others have reported similar behavior and no one has come up with an explanation. I've tried numerous thermostats, including one with a movable sleeve that covers up the bypass port when it opens.

You could get an infrared 'no-touch' thermometer to get the actual temp of the radiator:

12:1 Infrared Laser Thermometer

Amazing deals on this 12:1 Infrared Laser Thermometer at Harbor Freight. Quality tools & low prices.

www.harborfreight.com

Thanks. I feel better now. On a 90 degree hot Florida day when moving still stays under 170 even 165. Will climb to 190 or more if I am stopped for say two long stop lights if outside temp in 90's. Once moving drops to 162 or so in just a block. Came with Aluminum radiator of unknown size. My thought was that oil needed 180 to help keep contaminants out. I worry too much, lol. I will use my infrared on touch next time out. Thanks

 

[Martinld123]

Both my BN2 and BJ8 behave similarly. On a cool day, they won't go over 160deg or so unless idling for a couple minutes. On a warm day, they cruise at 180 as you'd expect, and heat up at idle even quicker, sometimes approaching 200 or more. Others have reported similar behavior and no one has come up with an explanation. I've tried numerous thermostats, including one with a movable sleeve that covers up the bypass port when it opens.

You could get an infrared 'no-touch' thermometer to get the actual temp of the radiator:

12:1 Infrared Laser Thermometer

Amazing deals on this 12:1 Infrared Laser Thermometer at Harbor Freight. Quality tools & low prices.

www.harborfreight.com

Yes, this answers my question. I can see stat opening at 180 but not showing that temp at gauge because radiator is doing it's job. Thanks

 

[Bob_Spidell]

Try as I might, I can't come up with a Law of Thermodynamics that explains this phenomenon. Up to a certain ambient temp, the heavy iron block is able to dissipate its heat, even with a closed thermostat. But, above 80deg or so ambient, even full flow through the radiator allows heat to build at idle. Makes no sense, and even the two different engines--4-cyl vs 6-cyl--act the same. Go figure.

 

[Rob Glasgow]

Speaking of checking gauge accuracy, I couldn't resist posting this pic (of a gauge from a BN2!) once again:

View attachment 75690​

Reid, Quick, shut off the engine. You’ve got no oil pressure…..

 

[John Turney]

Try as I might, I can't come up with a Law of Thermodynamics that explains this phenomenon. Up to a certain ambient temp, the heavy iron block is able to dissipate its heat, even with a closed thermostat. But, above 80deg or so ambient, even full flow through the radiator allows heat to build at idle. Makes no sense, and even the two different engines--4-cyl vs 6-cyl--act the same. Go figure.

The reason temperature increases at idle is the lack of air flow. While the fan will provide some air flow, they tend to be rather inefficient.

 

[roscoe]

Perhaps the speed that the water pump is moving water plays a role. I used to have a 1942 Ford 9N tractor that I used for mowing. Often times, I'd be mowing along on a 90 degree day and everything was fine, there was no water temperature gage but oil pressure was good. I soon learned that when these conditions existed, if I throttled back to get off the tractor there would almost immediately be a boil over. This model had an unpressurized cooling system so there was no thermostat and not a good seal at the radiator cap. The point being, that when the water flow rate through the block dininished as going from high rpm to idle, it alowed the water to boil in the block. If I maintained the higher flow it would keep it just below boiling on most occasions. The water in the block is moving more slowly at idle and thus picks up more heat from the engine. It usually meant the end of my mowing session as the magneto is just below where the rad cap is and it would soak the mag and coil and short it out until they dried. I learned to never throttle back unless I was where I wanted to park it. Old Faithful is now a farm ornament.

 

[Bob_Spidell]

The reason temperature increases at idle is the lack of air flow. While the fan will provide some air flow, they tend to be rather inefficient.

Of course, but that doesn't explain why the temp doesn't reach the thermostat's opening temp at speed on a cool day. A thermostat's job is to maintain a minimum engine temp, for operating efficiency and for an effective heater and defroster. With combustion, the engine should get hotter and hotter until the thermostat opens. From new, my Ranger would never reach nominal operating temp at any speed or idle, until I finally put a new thermostat in it, now the temp bounces around but mostly stays in the 'normal' range. Presumably the original thermostat was stuck open.