Accuracy Of Tim Temp Gauges Versus Infra-Red Meter

Hi all,

 

I've been trying to get to the bottom of very hot engine temperatures which started occurring a few months ago.

 

I was getting readings of around 75-80% (i.e. halfway between Medium and Hot) on the standard Nippon gauge.

So I flushed the rad+heater,  replaced the coolant, fitted a new 82deg thermostat,  fitted a new 15lb rad cap,  replaced the temp sender with a new one from a well-known supplier,    but to no avail,    the temp was still showing 75-80%.       Coolant seems to be staying reasonably clean and blue after flushing.

 

So I suspected the voltage stabiliser (after all,  I did have the gauges apart a couple of times last year and the workings of the fuel/temp gauge look very delicate indeed,  so could easily have been damaged).

I isolated the built-in stabiliser and connected a new solid-state 10V stabiliser,   but no success - the Nippon gauge was showing 80+%   (with the new sender it seemed to be climbing even higher).

The new solid-state stabiliser was definitely working well,  throwing out 10V according to the multimeter.

 

So getting cheesed off,   I installed a TIM electric gauge supplied with matching sender.

But after just 15 minutes of driving,   this gauge too is showing 100 degC !!

It has an 82deg thermostat so it really shouldn't be running much above 82.

 

Now you would think this just doubly confirms that there's an engine issue,   but my infra-red meter shows considerably lower readings  (see first photo):

 

 mini - infrared readings.jpg   74.43K   5 downloads

 

     - half an inch above sender,  83 deg

     - an inch above sender, 95 deg

     - flat machined surface of cylinder head, 96 deg

     - side of thermostat housing, 96 deg

     - top of thermostat housing, 85 deg

     - radiator header tank, 83 deg

     - meanwhile,  TIM gauge indicated temperature, 102 deg   !!!

 

(I did these readings many times on several occasions and I get these results fairly consistently)

(Interesting, a few locations consistently show 83-85,  which would be about right for my thermostat which is 82).

 

 TIM gauge reading.jpg   51.93K   10 downloads

 

My questions:

 

1. Which is likely to be more accurate,  the infra-red readings or the TIM electric gauge?

2. What is the best place to take an infra-red reading?    They vary so much by location!     (I'm holding it 35cm away as per instructions)

3. Has anyone else had experience of a TIM gauge reading far too high?

4. What is the best way to figure out if my engine really is running so hot?

5. Leaving aside the possibility of gauge inaccuracy,  at what engine temp should you pull over and stop driving?    How hot is dangerous enough to start causing damage?   100deg?   105deg?

 

Also:

 

5.  On the first photo,  it can be seen that my fan is only 1/3rd of the way into the cowl,  as shown by the clean sections on the tips of the blades.    Most of the fan is outside the cowl.    It currently has one 4mm spacer on it,  as per factory standard.   Do I need to add more spacers?    How far in should it be?

 

 

 

 

Does the Tim gauge  need a 12 or a 10v feed? 

The Tim gauge has its own built-in voltage stabiliser, the instructions say to supply it directly from a live feed (ie. 13.8V) so this is what I've done, I've simply taken an extra wire using a ring terminal from the back of the Nippon PCB, on the track where the Nippon fuel/temp gauges get their 13.8V live feed from. Multimeter confirms it's 13.8V.

I feel your frustration but a few things to think about.

82C is what your Tstat is labelled but they are not a very accurate device and the temp can easily go above that anyway.

the infrared "pistol" cannot sample 1/2 inch increments, the laser dot is merely an indicator, the sample area is about an inch taken by the lens so the further from the object the larger the sample area. Think of it as fanning out from the lens.

The accuracy or otherwise of a gauge is all dependant on how it is set. two identical gauges may read differently.

One sure way of finding out if your engine is overheating is with a traditional thermometer tested to prove its accuracy. Run the engine up without the rad cap on and measure the water in the rad using a 120C thermometer.

Do a calibration check of one of your instruments, probably the infrared one would be easiest.

 

Point it at a can of beer, straight from the fridge, but get in about 40 - 50 mm away from them, that'll be around 4^oC.  Then do the same with some just boiled (but no longer bubbling) hot water - the the surface, that will be 100^oC +/- 5 degrees. Don't fret too much if it's out at either end of these ranges, just not what temps it's giving you. Then you can compare your other gauges against the IR Gun readings.

Try and get in close with the IR gun - 40 - 50 mm, the further away you are, the bigger the picture it will measure and usually average over that area.

 

Also, as course as it may seem, I can feel the temp of the air coming through the radiator, I can say what temps they are, but I know what's in the normal range and I know what's quite hot from that. Maybe I've been drinking Petrol and Brake Fluid Cocktails for too long ? But if you say have a feel of the air from your daily driver, that'll have a normal running temp of circa 90 degrees as a guide, but in feeling it, you need to 'feel' past the flow volume of air and seek out the temperature of it.

 

Hmmm,,,, I'm thirst now,,,,,

Is the OP,s fan on backwards?

Is the OP,s fan on backwards?

I would say no. If it was I think we could see more detail of the hub. As we can’t see much detail I would say the smooth side is towards the engine.

Note that the tstat rated temp of 82 deg determines when it should be fully open it does not set the max temp of the engine coolant. It is the heat produced at a given time versus heat removed via rad that determine max temps in the system. Tstat just ensures engine reaches its minimum desired operating temp quickly after start up.

You should always test a new tstat in a pot of water heating on a stove with a thermometer to see when it fully opens. I've had new ones fail to open fully. That will give you high engine temps.

You said you replaced coolant. Did you perform a descaling treatment? This can help restore poor heat removal.
What is the condition of the water pump?

Is the OP,s fan on backwards?

 

Although it's too dark to see in the photo,  I checked this,    the smooth side is definitely facing the engine,   the ribbed side facing the rad.

 

 

You should always test a new tstat in a pot of water heating on a stove with a thermometer to see when it fully opens. I've had new ones fail to open fully. That will give you high engine temps.

 

I did this just before fitting it,  it looked as though it opened fully at around 82-85deg  -  or at least a substantial gap opened up,   I'm not experienced enough to know how far 'fully' is so I could have misinterpreted this.

 

 

You said you replaced coolant. Did you perform a descaling treatment? This can help restore poor heat removal.

 

I used Wynn's Rad Flush which claims to "remove scales and eliminate rust".

Then I fully flushed with water to remove any traces of Rad Flush and replaced with coolant   (approx 30% glycol to 70% water if I remember correctly).

 

 

What is the condition of the water pump?

 

I haven't checked this,   although it was a brand new pump 3 years ago when the engine builder supplied the engine  (it's done 6350 miles since).     I do have another new one sitting on a shelf which I was planning to fit if all else fails,  but I'm never eager to mess with anything that involves gaskets in case I can't get the gasket to seal properly again!!       

 

 

 

 

I'm planning sometime this week to check the temp sender in a pan of boiled water.

To do this I'll need to have the gauge working (i.e. ignition key position 2) without the engine running.

The instructions to my electronic ignition said to never leave the ignition powered without running the engine (and indeed,  after 10 seconds or so I hear a very unhealthy sounding rapid clicking).

What's the best way to disable the electronic ignition?     Simply pull the negative spade from the coil?

Edited by zero_wlv, 12 September 2021 - 09:08 AM.

The temp gauge sender normally needs to ground to engine block to close circuit. So if trying to test it in pot of boiling water you'll have to rig a ground line to engine.
Yes to disable ign just disconnect the power lead running to the trigger board into the dizzy.

You really need to confirm actual coolant or engine temp via something other than the infrared device, which is as mentioned earlier, very dependant on what is in the measuring field of view. The red laser dot is not the measurement area, just a general direction guide. Anything significantly cooler in view will drop the average reading significantly. How about an old fashioned mercury/alcohol/bi-metal type thermometer, like an oven meat thermo, placed on engine block or even dipped in rad fluid as engine is brought up to temp? It will boil a bit above 100 C as its glycol mix, not straight water and not under pressure if cap is off. If it reaches 90-95 or so and holds there you know its not actually running too hot and the instruments are incorrect.

The temp gauge sender normally needs to ground to engine block to close circuit. So if trying to test it in pot of boiling water you'll have to rig a ground line to engine.
Yes to disable ign just disconnect the power lead running to the trigger board into the dizzy.

You really need to confirm actual coolant or engine temp via something other than the infrared device, which is as mentioned earlier, very dependant on what is in the measuring field of view. The red laser dot is not the measurement area, just a general direction guide. Anything significantly cooler in view will drop the average reading significantly. How about an old fashioned mercury/alcohol/bi-metal type thermometer, like an oven meat thermo, placed on engine block or even dipped in rad fluid as engine is brought up to temp? It will boil a bit above 100 C as its glycol mix, not straight water and not under pressure if cap is off. If it reaches 90-95 or so and holds there you know its not actually running too hot and the instruments are incorrect.

 

Thanks for the replies everyone  -  one the nights this week I'm gonna try the experiment with a bowl of boiling water,   letting it cool and taking measurements every so often.

I'll do this for the TIM gauge and also the original Rover gauge while I'm at it  (I still have the old sender).     I have a digital kitchen thermometer and an old fashioned mechanical meat thermometer so will use them both out of interest.

I've noted the advice above about earthing the temp senders when they're out of the car.

 

I'll post the results back here when I get them.

 

At least then I'll have some idea whether I'm actually dealing with an engine problem or just inaccurate gauges.

 

Thanks for the replies everyone  -  one the nights this week I'm gonna try the experiment with a bowl of boiling water,   letting it cool and taking measurements every so often.

 

I know remote temperature sensors can struggle with reflective surfaces and water might well be sensitive to reading angle. Perhaps put some spare engine part in the water and when everything is at 100 degrees take it out and compare readings?

Although your engine is not overheating ( boiling) there are some things to consider that may make it run hotter than before ( I'm assuming the gauge has been at normal after engine rebuild) .

Warm weather, the fan does look as if it should be closer to the rad or the rad closer to the engine.

Advanced timing, If the dizzy has moved a little or the advance mechanisms are stuck.  

Fuel mixture, a lean mixture, clogged filter can heat up the engine.

Although your engine is not overheating ( boiling) there are some things to consider that may make it run hotter than before ( I'm assuming the gauge has been at normal after engine rebuild) .

Warm weather, the fan does look as if it should be closer to the rad or the rad closer to the engine.

Advanced timing, If the dizzy has moved a little or the advance mechanisms are stuck.  

Fuel mixture, a lean mixture, clogged filter can heat up the engine.

 

Hi viz139,  yes the gauge spent about three years at or just below normal after the engine was originally rebuilt.

As for advanced timing,   I recently advanced it to 13deg,  it was previously at 10deg,   I only did this because I thought advancing it a bit might help the running temperature.   Either way, it made no difference to the temp.

The recent MOT test showed 2.68%  CO reading at idle so hopefully the mixture's not particularly lean.

Well I said I'd give an update on how accurate the temperature gauges are so here it is,   the setup I used was just an oven dish full of boiling water:

 

 temp comparison.png   139.72K   0 downloads

 test setup 2 .jpg   75.8K   2 downloads

 

Clearly I can't blame the high running temperatures on a faulty TIM gauge.

If anything the TIM gauge UNDERREADS by about 5degC,  (although I suspect this discrepancy might disappear when it's inserted into a cast iron engine block like it's meant to be, rather than a piece of plywood).

Obviously my Rover/NipponSeiki gauge is hopelessly inaccurate,  I'm not sure why,  I tested it with two different GTR101 senders and the voltage stabiliser is definitely kicking out 10V (9.75V to be precise).

 

Anyway,  it would seem that when the TIM gauge tells me the engine's running at 100-102degC,  it really means it.

Engine should be easy to keep cool as it's only a warmed over 998cc throwing out 60bhp.

 

I already replaced the thermostat and flushed with Wynn's Radflush a few months back,  and also tried adjusting the advance backwards and forwards.    All to no avail.

 

So I'm just gonna throw the boat at it now and:

 

1.  Flush engine by running it with 50/50 white vinegar/water then leaving it for a day before draining.  

2.  Fitting new water pump    (shouldn't really be necessary, it's only 3 years old)

3.  Fit additional fan spacer.

4.  Fitting new 2-core radiator    (although I'm sure the bog standard cheapo radiator should be ok for a 60bhp engine like this.    Only mistake I might have made with the existing rad is using tap water in it instead of distilled,   although our tap water is very, very soft so I didn't think it'd be a problem).

 

If anyone has any advice on how long to leave the vinegar in that'd be much appreciated,    I really don't know whether it should be a matter of hours,  days, or a week.

 

Also I've seen lots of posts on this forum recommending CLR,   so I went and bought a litre of Zep CLR from Screwfix.     However,  it turns out the active ingredient is phosphoric acid.     I think other posters in the States and Australia are referring to Jelmar CLR which it turns out is lactic acid.    So I'm not gonna risk it.     Unless someone has some experience of flushing an engine in-situ with phosphoric acid in which case it'd be great if they could share it.

 

Thanks in advance if anyone can offer any further advice/comments.