[Healeys] radiator thermostat

Wed Sep 17 20:11:05 MDT 2025

Something else to remember is that the temperature bulb is located either in the top tank of the radiator 100's & 100/6 or directly below the thermostat housing where the coolant which has passed through the radiator enters the engine. This means that the coolant in the engine and exiting from the engine is probably significantly hotter.
Has anyone actually measured the temperature of the coolant as it enters the radiator at the bottom?
It could well be that magic 185°F that an engine apparently requires for best operation occurs at a significantly lower indicated temperature.

M

________________________________
From: Healeys <healeys-bounces at autox.team.net> on behalf of richard mayor <boyracer466 at gmail.com>
Sent: Wednesday, September 17, 2025 7:09:14 PM
To: Leach Hank <gradea1 at charter.net>
Cc: Richard Antal <rantal243 at yahoo.com>; Healeys <healeys at autox.team.net>
Subject: Re: [Healeys] radiator thermostat

Hank makes a very good point about where to measure the water temp.  And to get an infrared temperature sensor.  I recently fired up a fresh V8 engine to break in the cam.  I had also bought a new water temp gauge with sensor.  The new  sensor was screwed into a port on the cylinder head.  As we were running the engine I saw the temp climb and approach 220 degrees but fortunately I had my infrared sensor.  The water temp was actually quite lower and I was able to take readings from various places in the system.  If I had relied solely on the gauge I would have freaked out and probably shut the engine down.

Just another example of the garbage that is being sold in the parts stores these days.

Richard Mayor
boyracer466 at gmail.com

On Sep 17, 2025, at 3:47 PM, Hank Leach <gradea1 at charter.net> wrote:

I would like to comment about the position of the temperature "sensor" found in the Healey. All of them-100s and 3000s measure the water/antifreeze temperature flowing thru the radiator. That is not necessarily the temperature of the engine itself. Using a heat detector gun (Harbor Freight) you can actually see the head, block and exhaust readings and they will be different than the degrees indicated which has been read in the water flowing and transferred down a long capillary tube to an analog gauge.

In contrast, most older American cars, and incidentally the Jensen-Healey, measure the temperature of the manifold, or the block, by electronic sensor to an analog gauge.

I'm sure todays' vehicles have more accurate measurements, but they don't tell us what that actual number is unless an icon illuminates on the dash indicating a problem with temperature. I guess that ancient type of measurement is what gives the Healey its charm. Be it Fahrenheit or Centigrade. Hank

--------------------

From: "Harold Manifold" <manifold at telus.net>
To: "Richard Mayor" <boyracer466 at gmail.com>
Cc: "Richard Antal" <rantal243 at yahoo.com>, "Healeys" <healeys at autox.team.net>
Sent: September 17, 2025 at 3:05 PM PDT
Subject: Re: [Healeys] radiator thermostat
Hi All,

Thermostats always generate interesting discussions.

I use a 180-degree thermostat in my car. However, what's equally important is how effectively the thermostat regulates the coolant temperature. A thermostat that is fully closed or fully open is no longer actively controlling the temperature. The normal operating range is typically the opening temperature plus 20 degrees. For example, a 165-degree thermostat should maintain the temperature between 165 and 185 degrees, while a 180-degree thermostat should keep it between 180 and 200 degrees.

If your current thermostat maintains the coolant temperature within its specified range under normal driving conditions, then it's the correct one for your needs.

Harold

On Wed, Sep 17, 2025 at 1:36 PM Richard Mayor <boyracer466 at gmail.com<mailto:boyracer466 at gmail.com>> wrote:
165 is too cold for good running.  Our engines run better in the 180 to 190 range.

Sent from my iPad

On Sep 17, 2025, at 12:13 PM, Robert Markovich via Healeys <healeys at autox.team.net<mailto:healeys at autox.team.net>> wrote:

165 is the one I use

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On Wednesday, September 17, 2025, 2:50 PM, Richard Antal via Healeys <healeys at autox.team.net<mailto:healeys at autox.team.net>> wrote:

Gents,
     What is the desired coolant temperature for optimal engine performance? I've searched the tech articles and can find nothing that specifically answers that question. This summer my BJ8 seemed to run fine with a 160 thermostat which, according to the gauge which I've checked and found to be accurate, kept the coolant at around 165. Thanks to all who respond.
rich antal
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