Checking Engine Temperature

[richardlamsdale]

The temperature gauge on my Coupe sits at the top of the green / bottom of the red when the engine is at a stable temperature. I have a new temp sensor fitted, and new hoses and thermostat. I realise the gauges aren't very accurate, but I'd like to verify whether it's just the gauge reading high.

Whats the best way to check this, other than swapping the gauge (I don't have a spare)? I have a hand-held infra-red thermometer, but does anyone know the best way to confirm the actual engine temp? Thanks.

[barryr]

Love to hear the answer to this also Richard as mine is exactly the same!
(and like you I point the laser at various bits but have no idea whats the right number to see!

[Phil Nottingham]

Either disconnect the sender and stop worrying if there are no other signs of overheating eg water loss or buy a digital thermometer that you just point at an object

[richardlamsdale]

I have a digital thermometer as mentioned, but where is best place to measure? I'd think different materials radiate heat at different rates, and the coolant will be at different temperatures at different locations. So is measuring at the manifold next to the sender and expecting about 95 degrees about right?

[lagain]

This is a slightly difficult one. I would imagine it is best to measure water temperature away from any other heat source, such as the manifolds, probably the top of the radiator as the water is heating the radiator rather than the engine which is heating the water.
If your guage sits at the top of the green what happens if you get stuck in traffic ? does it then go into the red ?

[enigmas]

Simply fit an additional mechanical temperature sensor under the bonnet either high up on the engine block or close to the thermostat housing.

[dhb5610]

Jun 7, 2019 12:30:39 GMT richardlamsdale said:

The temperature gauge on my Coupe sits at the top of the green / bottom of the red when the engine is at a stable temperature. I have a new temp sensor fitted, and new hoses and thermostat. I realise the gauges aren't very accurate, but I'd like to verify whether it's just the gauge reading high.

Whats the best way to check this, other than swapping the gauge (I don't have a spare)? I have a hand-held infra-red thermometer, but does anyone know the best way to confirm the actual engine temp? Thanks.

Having had my P5B Saloon for 3 years now and had similar experiences with the temperature gauge. I have had all the hoses replaced and the radiator replaced with a slightly larger core it still behaves in the same way. It initially goes up to the bottom of the red and drops back to normal and then stays there for the rest of the time. Having spent time chatting to other Rover owners I now accept that this is what it does rightly or wrongly it never looses coolant and there are no leaks so it's OK 

[Brendan69]

I have experienced this too with mine recently and after changing everything she still did the same albeit absolutely no signs anywhere of coolant loss or engine issues so I took advice from many off here and lived with it UNTIL I recently had mine set up and tuned on a rolling road after I completed a full service.

Now she runs a lot better, starts better and the temp guage reading now sits below the red line section and nearer to the middle of the green albeit just above centre which I am happy with.

Regards,

[djm16]

The colour of an object is the light that is returned to the eye when the object is illuminated with white light. Most materials under the hood will be effectively a "black body" at infrared frequencies, in which case the distribution of emitted infrared will be approximated by Planck's Law.

In other words, the IR scanning thermometer will be reasonably accurate on most surfaces you are likely to encounter.

When I check my engine temperature, there is a small variation of the measured temperature from the nominal thermostat value. The closet to 77C are the thermostat housing and top radiator pipe, and the engine block. The head(s) near the exhaust manifold tend to be a little hotter, 85-90C.

If you are getting 90C+ around the thermostat housing and you have a 77C thermostat in place, then either the thermostat is faulty or the radiator is providing inadequate cooling.

[richardlamsdale]

Thanks everyone - really useful. This seems to be a common issue, and I'm happy to live with it if I can verify the engine isn't actually running too hot. I'll take some measurements and report back.

[richardlamsdale]

Having checked the temperatures with the IR thermometer today I'm thinking (unsurprisingly) the issue is the sender or the gauge, and the engine isn't running hot. At a stable engine temperature I get 85 degrees around the sender, and 75 degrees at the top of the radiator near the inlet. There's no sign of water leaks anywhere.

[Ken Nelson]

I have the same problem with the temp gauge in my Coupe. It wanders anywhere between high normal to mid-red range. I replaced the voltage stabilizer and used a digital thermometer to verify that engine is no more than 180ºF (82ºC) during this, so the fault is with the gauge. Other cars manage to make their electric temp gauges work. How come Rover couldn't, and isn't there someone out there who would be able to repair/correct these gauges??

[Brendan69]

These things are set to  try and test us I say so unless we have coolant leaking out all over the place and or lots of steam and an engine which wont go anywhere i'd say all is well and live with it and carryout regular pre-drive checks from cold each time you take your pride and joy out for a drive and give her a check throughout the trip and once back home after she has cooled down a bit. Its all belt and braces tactics and also has a plus side as if something is amiss under the bonnet your are more likely to spot it earlier than on the move.

I have a small box in my boot with emergency spares too JUST IN CASE as pretty much no AA or RAC man today will have ever worked on a P5B.

Regards,

[Warwick]

Don't forget that those digital infra-red thermometers usually have a conical sensing area. By that I mean that the surface area being measured is circular, and the further away from it the thermometer is, the bigger the circle. They usually have a diagram on the device that shows the diameter of that circle in relation to the distance from the object being measured.
So to measure a small area, you need to be quite close to it, otherwise you're basically measuring the average temperature of everything in that circle. The laser is just to assist in aiming the thermometer. The red dot is in the centre of the circular area being measured.

For example, mine has a ratio of 8:1, Distance to circle diameter.
If the instrument is 200mm away from the target, the area being measured is a circle with a 25mm diameter.
At 400mm it's 50mm. At 800mm it's 100mm. At 1,600mm it's 200mm, and so on.

EDIT:
I should point out that I didn't buy mine to use on the car. It was bought to determine where the insulation batts were in the house ceiling, in the middle of summer. I haven't used it on a car, except out of curiosity, to compare the top and bottom radiator tanks on the old Range Rover.

[Deleted]

I bought one of those infra red temperature thingies but after a while didn't bother as if the thing isn't boiling or blowing out clouds of steam after a long run there can't be much wrong with it. 
I bought one of those cameras with a three foot long probe and spent the next few weeks poking it into all sorts of orifices on my car collection and managing to put the wind up myself countless times until I realised that the picture on its screen can be upside down or at any angle depending on the contortions the lens has performed getting to its destination. I was getting ready on one occasion to weld a hole in a sill section that was in fact a sound,non rusted drain hole.Maybe we sometimes over complicate things.
My water temp gauge isn't accurate,I doubt many are,but if it starts to climb and then drop a bit as the thermostat opens it would seem to indicate all is functioning as it should.

[digger]

With the car just idling in the garage or driveway, roughly how long does it take to come up to temp?  Ambient is around 20 degrees C, bonnet up.
It seems to take ages to move to just above the C in COLD.  I lose patience waiting for it to get higher, the fuel gauge seems to go down faster than the temp goes up!.  It still has the mechanical fan and has a new temp sender.  The top hose is cold while the lower hose is warm.  My next check is to confirm that it actually has a thermostat.  I've got no other cars with 'always blowing' mechanical fans so have nothing to compare with.

[Phil Nottingham]

If the top hose remains cold it will have a stat. It can take some time to heat up just idling. Does the heater warm up?  It is not a good idea to let it it idle for long periods as the oil pressure will be too low and this has to heat up too. If it cannot be driven on the road then a fast idle is better

[lagain]

Best to start and drive. It is not a good idea to just run the engine up to temperature and then turn it off as this causes condensation in the engine and exhaust, with possibly emulsifying of the oil - where it goes creamy and also sooty plugs.
When I lay my car up for the winter I turn her off and do not start up again until the spring, when she always goes first turn of the key. Incidentally, it helps after a long lay up through the winter to turn the engine with the choke pushed in until the oil pressure needle moves, perhaps 10 seconds and then pull the choke out and let her fire up.