Thread: VDO water temperature gauge - electrical or mechanical?

Originally Posted by Aaron IIA

Most pressure gauges now come with a nylon capillary, but even if you have copper, if can be replaced with nylon.

Aaron

I recently did a mechanical oil pressure gauge install using nylon tube. The nylon tube has a tendency to kink if not well routed which is a worry as it presumably weakens the tube and increases risk of rupture.

That said, I was replacing the tube as the previous copper tube had been torched due to the end of it once falling onto a live terminal at the starter solenoid, which immediately heated the oil inside so it ran out and ignited and burnt all manner of wiring nearby. It also shorted along the tube and caused all sorts of issues at the gauge binnacle!!! At least nylon tube will not do that!

Having fun.....
Chris

Reviving this very helpful discussion, thanks all. I’m looking at fitting a coolant temp gauge to the puma. Assume all of the above applies.

Dumb question 1: Where is the best location for the sensor itself? In the expansion tank?

Dumb question 2: What’s the consensus on the reliability of OBD port scan type guages - Engine Temp readings? Are these more reliable? Or are they reading from the same sensor as the original temp guage?

Hi Zeros, I can't comment on the Puma which would obviously have coolant sensors for operation. One of these locations may be the spot to use with a two way fitting, I will read what others advise with interest.

I don't think the tank would be a useful location. You need a reading from the coolant which is in the head.

Thanks, yes I assume it would be more a coolant loss sensor than temp in the expansion tank.

I’ll have a closer look at where the sensor might be on the head. Any advice much appreciated.

Originally Posted by Zeros

....

Dumb question 2: What’s the consensus on the reliability of OBD port scan type guages - Engine Temp readings? Are these more reliable? Or are they reading from the same sensor as the original temp guage?

Dunno about reliability, but so far my experience with accuracy has been good, or excellent!
I've used cheapo OBD plugs for a few years now on various cars(couple of Japs, and recently a Peugeot(dads) and my own D2 V8 .. all been within a couple of degrees(using an IR temp gun).
Actually, the temp gun is the device most likely to give 'false readings' in a manner of speaking as the engine will have hot spots .. ie. some spots hotter than others.

The OBDII devices read the sensor readings that all go to the ECU.
The cars temp gauge also reads from the ECU .. not directly from the sensor.
So yes, in a manner of speaking, the OBD device reads the same info as the temp gauge.
But note that as has been claimed many times over that many temp gauges are dangerously inaccurate, and may show overheating after the overheating event .. it's not due to the sensor.
It'll be due to the way the temp gauge is set to display .. whether that means the temp gauge itself is slow to react, or the ECU is programmed to show temps that way.

And note that it's not just LR temp gauges that display this way.
Brother used to have a Patrol a few years back, and it blew it's hoses and overheated way after the temp gauge rose to the red mark too!

Originally Posted by AK83

Dunno about reliability, but so far my experience with accuracy has been good, or excellent!
I've used cheapo OBD plugs for a few years now on various cars(couple of Japs, and recently a Peugeot(dads) and my own D2 V8 .. all been within a couple of degrees(using an IR temp gun).
Actually, the temp gun is the device most likely to give 'false readings' in a manner of speaking as the engine will have hot spots .. ie. some spots hotter than others.

The OBDII devices read the sensor readings that all go to the ECU.
The cars temp gauge also reads from the ECU .. not directly from the sensor.
So yes, in a manner of speaking, the OBD device reads the same info as the temp gauge.
But note that as has been claimed many times over that many temp gauges are dangerously inaccurate, and may show overheating after the overheating event .. it's not due to the sensor.
It'll be due to the way the temp gauge is set to display .. whether that means the temp gauge itself is slow to react, or the ECU is programmed to show temps that way.

And note that it's not just LR temp gauges that display this way.
Brother used to have a Patrol a few years back, and it blew it's hoses and overheated way after the temp gauge rose to the red mark too!

Thanks Arthur. Reliability as in can you rely on them? and/or accuracy.

Ok so OBD devices should be better at reading the temp as read by the ECU. And you can watch the temp live, rather than rely on the flicker of a needle. ....So does that mean that an OBD guage temp reading would be just as reliable as a separately installed aftermarket temp guage?

I recently fitted a VDO mechanical water temp and had a few issues come up after the install. I installed mech VDO gauges where I could during the rebuild (oil,boost, water).

Almost straight away it would bounce around between 75-85 deg when you hit a bump. Outside of this temp range the needle is stable as you expect.

On longer journeys I had the needle climb to 115 deg relatively quickly whenever the truck was pointed up hill ( and at other time but less frequently), very worrying at first. But would immediately drop 2-4 deg when shut off and sometimes come back to 85 faster than it would be possible for the engine too cool down....if it was actually that hot, which it was not. It didn't feel hot and certainly didn't smell like a hot engine should.

It gave me grey hairs whilst away on a maiden voyage post rebuild (engine/gear box/full re-wire/new interior etc etc)...as soon as I could I got a heat gun on it I did and confirmed what I thought. The engine ran at 80-85 no matter what, every heat gun reading was just above 80 when the VDO guage read something above 100.

Given the limitations with the water temp gauge (once it's in that's it...good luck getting it out without damage) and the troubles I've had, I'm somewhat soured on the mech water unit in my 130 and will fit an electronic jobby shortly. This is a big thing for me as I am a big believer in keeping things non-electronic where possible ie I swapped out a Td5 for a 4BD1

Originally Posted by Zeros

Reviving this very helpful discussion, thanks all. I’m looking at fitting a coolant temp gauge to the puma. Assume all of the above applies.

Dumb question 1: Where is the best location for the sensor itself? In the expansion tank?

Dumb question 2: What’s the consensus on the reliability of OBD port scan type guages - Engine Temp readings? Are these more reliable? Or are they reading from the same sensor as the original temp guage?

There is never a dumb question

I'll play devils advocate here - you already have a water temp gauge in the puma which should provide about the same response time as a second gauge so what is the problem you want to solve?

My direct responses...
1. I would not drill into the expansion tank.
a) it is plastic and bad mojo to tamper with it.
b) even if you replaced it with a metal version it is "away" from the main flow of water from the engine and would report a lower temperature than the main water flow.
c) so a secondary sensor should go somewhere around the radiator/water pump/engine block

2. Having a digital readout more precise.
a) This will make it easier to learn the nuances of the car ..eg sits at 85-87C pottering around the city. Can go up to 95C under load. etc etc ... so it helps you spot strange behaviour
b) most analogue meters have a very slow response time (just the way they work/part of the ruggedness)
c) some good commentary in the link below

Value of a Nanocom for 'Light' Work