Trying to get an accurate water temperature reading

[jazzdude]

I am trying to calibrate my water temperature gauge for the Range Rover sender with an IR gun.

Thought the area just around the otter switch was a sensible place and the fans switched on and off at a measured 92 & 87 deg respectively as the car warmed up on tickover from cold.

I then took the car out for a 'spirited' short drive and when I got back, measuring again at the same place found the fans switching on and off for a similar length of time as before but the readings were between 105-110 deg. I suspect this may be because of heat coming off the manifolds affecting the readings.

The otter switch seems to be working in that the fans are coming on and off but where is there on the car that I can get a better reading?

I have a Rovergauge and know that also measures temp, but I want to check that that is also working correctly.

[Steve_D]

I agree you can't trust the gauge on the dash with the standard TVR setup.
However I find it strange that you seem to want to trust the IR sensor rather than the ECU sensor.

IR can give some quite random readings particularly on bright or reflective surfaces.

Steve

[jazzdude]

Yes I know, it's very random all over the cooling system where you think the coolant temperature on the same side of the radiator would be constant.

I have read quite a few threads on coolant temperature and many have said that the IR gun was useful.

[bobfather]

Although it is possible to read a temperature accurately people put too much importance on it. What is important is to be able to see the engine warm up and to get indication of temperature moving outside of a desired norm, the precise accuracy of the dash gauge is irrelevant and meaningless. The temperature of coolant within a running engine varies greatly, there isn't one exact temperature throughout, that is the purpose of the system. Hot around the cylinders, cooler in the radiator and between places the temperature will be somewhere in-between.

The advantage of the Rover temperature mod is to see temperature changes more quickly and to have the gauge reading from the same location as the ECU sender.

You should also note that the response time between the Rover gauge sender and the ECU sender is grossly different. The ECU sender responds to changes very quickly with the Rover sender following a minute or so later due to brass heat soak so it is impossible to gain the accuracy you seek until the temperature stabilises. That can be achieved very simply by zeroing the reading at normal running temperature. I fitting a link with a 100ohm fixed resistor and a 100ohm variable resistor and zero'd to the ECU reading via Rovergauge once the temperature reached a stable running temperature.



The pot adjuster can be removed when calibrated

Edited by bobfather on Friday 22 July 07:40

[jazzdude]

That's very useful information, thanks.

How likely is it that the ECU sender be inaccurate, ie, if it is not very likely,then I will just use the Rovergauge + variable resistor to find the point on the guage where the temperature reads, say 92 deg, to correspond with the starting of the fans.

A query though, even if the fans come on at 92 deg, how likely is it for a system that is 'working properly' to carry on heating up to say 100 deg and staying up there, regardless of the fans being on? Is there a limit to the cooling capability of the twin fans?

In the case I described in my first post, the fans were cutting on and off even though the gauge, and my 'readings' were over the 92-87 deg range of assisted cooling.

[bobfather]

jazzdude said:

That's very useful information, thanks.

How likely is it that the ECU sender be inaccurate, ie, if it is not very likely,then I will just use the Rovergauge + variable resistor to find the point on the guage where the temperature reads, say 92 deg, to correspond with the starting of the fans.

A query though, even if the fans come on at 92 deg, how likely is it for a system that is 'working properly' to carry on heating up to say 100 deg and staying up there, regardless of the fans being on? Is there a limit to the cooling capability of the twin fans?

In the case I described in my first post, the fans were cutting on and off even though the gauge, and my 'readings' were over the 92-87 deg range of assisted cooling.

I don't think the ECU sender will be accurate, I believe it'll be accurate enough for controlling the fuel mixture

Setting the gauge to read right when the fans cut will not be accurate either, the otter switch is in a different location reading a different temperature coolant and otter switches are not accurate devices

Once the fans cut in I see the temperature via my Rover sender respond very quickly, 60 seconds or so.

Sorry that I haven't got a solution for you, I think the issue here is that chasing ultimate accuracy may be a fools mission. I have fitted Rover sender mods to three cars now and none of them were correct with the suggested 170ohm or 120ohm fixed resistor link. They were all different but all in the vicinity of 120-130ohms. If you have a 120ohm link then false high gauge readings would be very likely

[jazzdude]

After using a variable resistor, I found that the closest was around 120 ohm to read the gauge at 92 deg, when the fans kicked in. The problem is I am driving around and the gauge is showing between 90 deg and about 98.

I will check it against the Rovergauge while driving around to see what the ECU sender thinks the temperature is.

I have a couple of more modern cars, whose temp gauges do not budge from the middle setting whether you are driving up a cliff or down it, and a 320CE cabrio where the temp gauge goes up and down all the time. But at least you know it is right so you dont worry about it.

I cant understand why TVR were so relaxed about what is a major issue on an engine that generates so much heat, with a cat sat in front of it, that they didnt think to get this one part right.

[QBee]

I have had my Chimaera for four years and 32,000 miles.

General spring/cool summer running is around 70-80 degrees, up to 90 if stuck in traffic, but the fans cut in and cool the engine down to low 80s on the gauge.
This week's mini heatwave in the UK it has been 30 degrees air temperature.
Driving around in the TVR, my gauge indicated up to 105 degrees in traffic, fans running constantly, and they struggled to get it back down under 100 degrees until I found some nice straight dual carriageway to cruise at 70 in 5th, when it eventually came down to the mid-80s.

Jazzdude, your profile says "Cyprus".
My wife lived there as a child (Akrotiri of course), and assures me you can fry eggs on the pavement at 6am.
Perhaps that is part of your problem?
Solution?
Move to Rekjavik.

[jazzdude]

That's right we are in Cyprus and the car is handling the heat really well considering it is usually what you had in the UK for a few days, all summer here.

The car hasn't overheated yet and so far it is not looking likely to, I just want to be better informed about the state of coolant temperature and where the limits actually are.

[portzi]

jazzdude said:

That's right we are in Cyprus and the car is handling the heat really well considering it is usually what you had in the UK for a few days, all summer here.

The car hasn't overheated yet and so far it is not looking likely to, I just want to be better informed about the state of coolant temperature and where the limits actually are.

I can second that, I am living at Akrotiri, and Steve treated me to a spin in his chim down in Limassol, he was flooring it as the Cops arnt as keen as our Rossers in the UK, and it never overheated once

[portzi]

QBee said:

I have had my Chimaera for four years and 32,000 miles.

General spring/cool summer running is around 70-80 degrees, up to 90 if stuck in traffic, but the fans cut in and cool the engine down to low 80s on the gauge.
This week's mini heatwave in the UK it has been 30 degrees air temperature.
Driving around in the TVR, my gauge indicated up to 105 degrees in traffic, fans running constantly, and they struggled to get it back down under 100 degrees until I found some nice straight dual carriageway to cruise at 70 in 5th, when it eventually came down to the mid-80s.

Jazzdude, your profile says "Cyprus".
My wife lived there as a child (Akrotiri of course), and assures me you can fry eggs on the pavement at 6am.
Perhaps that is part of your problem?
Solution?
Move to Rekjavik.

Pardon the Pun Anthony but was your wife a "Scaley Brat" as we call them when her parents were blue suiters at Akrotiri?

[QBee]

portzi said:

Pardon the Pun Anthony but was your wife a "Scaley Brat" as we call them when her parents were blue suiters at Akrotiri?

I asked her, she laughed and said "no, but I know what he means by that!". I asked what it means and she wouldn't tell me.
Her father was a flight sergeant in the operating theatre there in the mid-70s, and she and her three sisters were there as teenagers. Best days of her life, she says.

[portzi]

QBee said:

portzi said:

Pardon the Pun Anthony but was your wife a "Scaley Brat" as we call them when her parents were blue suiters at Akrotiri?

I asked her, she laughed and said "no, but I know what he means by that!". I asked what it means and she wouldn't tell me.
Her father was a flight sergeant in the operating theatre there in the mid-70s, and she and her three sisters were there as teenagers. Best days of her life, she says.

Yes Anthony your wife is correct she is'nt , and yes Cyprus is gods hidden country, the people are amazing, even the Ruskies that live here.

[QBee]

portzi said:

QBee said:

portzi said:

Pardon the Pun Anthony but was your wife a "Scaley Brat" as we call them when her parents were blue suiters at Akrotiri?

I asked her, she laughed and said "no, but I know what he means by that!". I asked what it means and she wouldn't tell me.
Her father was a flight sergeant in the operating theatre there in the mid-70s, and she and her three sisters were there as teenagers. Best days of her life, she says.

Yes Anthony your wife is correct she is'nt , and yes Cyprus is gods hidden country, the people are amazing, even the Ruskies that live here.

I googled it and found a lovely blog post by someone called Blodwyn, who was a child there about 5 years before my wife. Showed it to Erin Dawes, who said it brought back very fond memories of her time there.