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IanPatterson

Accurate measurement of coolant temperature

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I want to temporarily measure the coolant temperature accurately. My TR4A <seems> to run a bit hot, but I don't know if its just the gauge or something worse. So I am looking for a bit of kit that I can temporarily install to check the temperature against what the gauge is saying. Then can see if there is actually an issue.

Any ideas?

Ian.

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Infrared gun. About £30 these days.hold it close to the hose, press the trigger and - Make The Noise! - (it beeps). Displays the temp. Not perfect, but better thank ball park.

 

John

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Check the gauge by popping the sender in boiling water. The gauge should read 100 degC/212 degF.

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Same as John - i use an IR thermometer/gun.... works treat.... never tried it on the move though ;)

..... Andy

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With one of these or similar:

 

https://www.ebay.co.uk/itm/Digital-Thermocouple-Thermometer-Temperature-Dual-channel-Backlight-Meter-Tester-/162822487218

 

Just attach the end of the probe to the outside of the thermostat housing with aluminium sticky tape. It can read on the move unlike the optical gun others are recommending.

 

(It might even be possible to loosen the jubilee clip and poke the wire into the hose as its thin enough to seal again when tightened)

 

Since its two-channel you can measure the temperature of the return from the rad at the same time.

Edited by RobH

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I like the idea of the ebay product. Seems to do the job on the TR with the added additional use on my radiators in my house which have never been balanced.

Another job!

Will update when used. Probably more Q's when I find the actual temperatures.

Ian

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Hello, I run my 4a on 4life coolant supplied by MG Owners club with a Revotec fan and bottom mounted controller, perfect, gauge read 70 degrees and only wavered in standing traffic, that was before I fitted Efi, while I was rooting about with the temperature feed (I needed one for Efi) I replaced my old sender, the gauge now reads a steady 75 degrees bit, and it is a big but, the ECU tells me the engine temp is 85 degrees, before I wasn't worried, now I am! Something else to add to the list, cheers, Andrew

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Hi,

 

that's funny, I'm just coming from my workshop and made this for a friend.

 

post-13222-0-01122700-1529954897_thumb.jpg

 

We wants to fit it in the upper hose of his BMW 320 318 Typ E30 because the new BMW instument costs 200 Euro.

This thermometer is about 6 Euros at eBay and 30 minutes work on my late.

 

For a temporary use I would like to recommend to tape it on the hose, put some isolation and more tape around.

 

A laser thermometer is nice to have but how do you want to use it while driving?

And - the display differs very much depending of the surface (alu, rubber, rust, paint) you are targeting.

 

See the attached photo I made with the infrared camera of your office some years ago.

All the valve cover of this Alfa has all over the same temperature but looks different hot.

 

post-13222-0-95972900-1529954886_thumb.jpg

 

And my TR4A is not more hot than the MB 280 SL after 1 h out at 10°C, and the tyre is also not hot.

It only looks like this because the rate of refelction is different.

 

post-13222-0-49513600-1529954903_thumb.jpg

 

Believe it or not - it's true.

 

Ciao

Marco

Edited by Z320

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Now I am confused. As a newbie to TR4's (any), I thought this would be simple!. I have the workshop manual with suggested temperatures hence the original question. Unless anyone has other views I may go with the Ebay solution and just see what it says. For 14 Quid it seems like a reasonable way of getting the <accurate> temperature. But nothings that simple is it?

Ian

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Hi Ian,

what is actually happening to make you think things are a little too hot.

Has this happened just recently

What value thermostat are you using.

What sort of speed

Where are you driving - town/country/

 

Roger

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A few years ago i installed a cheap ebay sourced temp,sensor inside the air tube on my 6

 

The readings were fascinating, up to 70c in traffic !

 

So id recommend something along the lines Marco suggests, taped in place should be good enough for testing.

 

Steve

 

Ps, actually i probably still have that guage, built into a smiths 2 instrument, you could borrow it Ian if youre localish to surrey?

Edited by Steves_TR6

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Slight problem to be aware of with an IR gun is the material you are pointing it at. For example a rubber hose will be "cooler" than the liquid within it.

 

You know that to be true because you can hold a hose containing boiling water, so stick to metals.

 

Alan

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Actually its more complicated than that, as Marco has pointed out Alan. In the case you quote there is a drop in the conducted temperature due to the thermal resistance of the material. For an IR gun The temperature measured will depend on the infra-red emissivity of the material. IR guns are calibrated to read correctly for 'black body' radiators with emissivity of unity and will under-read for everything else. This site has a table of relative emissivities for common materials (note that shiny metals are poor):

 

https://en.wikipedia.org/wiki/Emissivity

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Hi,

 

on most infra red guns you can adjust the emission rate.

Normaly they come with 90 - 95%, you can adjust that due to the material you want to measure.

The manual should tell you more.

 

But the emmision rate also depeneds to the angle you point the material.

You see that in the bumper of the Mercesdes 280 SL: some parts are 13,9°C warm, others -27°C ice cold.

 

To measure the correct temperature of a metal surface is some way like throwing bones in the druid days.

You have to know the temperature of the surface, then adjust the emmision rate on the gun until the display "fitts"

and than can further measure this material in the angle you pointed it when you adjusted the gun.

 

That's why 1) a not adjusted laser gun 2) on metal surfaces is only good to compare "more hot" or "less hot".

 

Problem with too hot cars is often that we are not used anymore the fact that the coolant temperature is rising and falling.

Todays producers protect us from these worries by fixing the display on one temperature, the arrow never moves.

 

Ciao Marco

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Being a retired instrument engineer i do like the look of the ebay item

It will be suprisingly accurate but easy to do a quick calibration with boiling water and ice as a back up check before using

I'd be tempted to fit one of the probes in the top hose permanently...it would slide in under the jubilee connection with a bit if wellseal for good measure

All sorted for less than £15!

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In answer to the question regarding why I think my TR4A is running hot:

The reading on the temp is gauge is quite steady and consistent. On a longish run on dual carriageway the gauge is just over half way in the winter and three quarters in the summer.

In the last few hot days it goes up to about 80% in traffic and back down to three quarters when cruising (60 - 70).

I am investing in the ebay sensor so will test & report next few days.

Ian

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RogerH:

This has been happening since I got the car about 2 years ago.

How do I know what the value of the Thermostat is?

(Remember I am a newbie to the mechanics of the beast).

Ian

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Hi Ian,

 

sorry me causing any confusion.

If you want I can make a thermowell for you to fit in the original thermostat housing

instead of the original sensor for temporary time. All you need to buy is such a sensor with LCD display.

 

https://www.ebay.de/itm/1-5m-lang-Thermometer-digital-LCD-50-110-C-Temperatur-Anzeige-Messer-Termometer/253461963466?ssPageName=STRK%3AMEBIDX%3AIT&var=552637932403&_trksid=p2060353.m2749.l2649

 

Ciao Marco

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RogerH:

This has been happening since I got the car about 2 years ago.

How do I know what the value of the Thermostat is?

(Remember I am a newbie to the mechanics of the beast).

Ian

Hi Ian,

the thermostat, inside the thermo housing on top of the cylinder head, has its value stamped on the thermostat itself. You need to remove it to see.

In theory opening up the thermo housing is easy peasy, but nothing on a TR is what it seems. If the big bolts have not been moved for a while they may be seized in.

It is worth having a look but be prepared for stiff bolts etc.

 

It sounds like you have a winter stat in the housing (82 or 86C). During a hot summer something like 76 C would be worth putting in.

 

Where abouts are you based. If in the UK have you popped in to see your local group.

Roger

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Hi Ian,

at least you now know the value. No need for shrouded stat on your engine.

 

I assume you are running on water + antifreeze; nothing fancy.

 

Has the radiator got a decent duct leading into it.?

 

Roger

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Don't know about the coolant. Its the same as when I got it 2 years ago. It will be replaced when I do the fan.

By duct I presume the top hose? If so it looks new.

 

One thing that disturbs me is that the water at the top of the rad has some brown sludge around the filler cap. There wasn't any sludge in the thermostat housing.

The water in the plastic overflow bottle looks clean and blue.

 

When I get the temperature checker kit I will be able to tell if there is a reasonable temp drop between the top and bottom hoses.

Ian

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