Coolant temperature sensor changing

Hi de hi,

In an effort to get the temperature gauge working, I've bought a new temperature sensor (genuine Ford one no less!).

It's the one under the coil pack near the top of the engine.

My question is, how much coolant am I going to have to drain before I can change it, or is it worth giving it the old switch-a-roo - slapping it in there and catching any spillage?

Hi Lee
That's what I'd do, have the new sensor ready to go straight in and you'll lose next to nowt.
Barry

The Arch Bishop said:

[post]346981[/post] My question is, how much coolant am I going to have to drain before I can change it, or is it worth giving it the old switch-a-roo - slapping it in there and catching any spillage?

Click to expand...

Either switch-a-roo and fast hands or clamp off the pipes from the expansion tank, with artery clamps or similar, and then a slower switch-a-roo. You'd lose under half a litre and get no air-locks.

System holds 6 litres in total and the idea of clamping is that water can't get out if air can't get in - you do it with central heating systems, etc. Maybe you've seen the trick with a full pint of beer with a beer mat on it and then turned upside down and the beer mat slid away? Same thing.

A man after my own heart Barry! I mean, what's the worst that can happen eh? :grin:

Cheers Frank, that's a good idea - I've a set of mole grips that should do the job on the pipe. I did think of cling-filming the filler and then putting the expansion cap on, but then realised that there was too many other breathers running off of the bottle. Clamping it further down the system is a far better method!

The Arch Bishop said:

[post]346985[/post] Clamping it further down the system is a far better method!

Click to expand...

Effective hose clamping can be tricky *, but you'll slow the flow for sure. That high up the engine you're looking at 3 litres max, so a washing up bowl already under, will be your fall back position.

* central heating stuff is done using bungs or temp. compression stop-ends.

A cup full at most I'm sure you'll manage it Lee.
Barry

I'll be sure to let you know!

Ooo - about half a cup. It chucked that out and then just stopped (probably because of Frank's advice)!

Quick switch and back together. Gauge still dead on the dashboard... Pants.

First thought - air lock from changing the sensor. The level in the expansion tank hasn't moved yet so it could be that the sensor is operating in a pocket of trapped air.

Second thought - I'm not great on electrics, so is there any chance that this sensor gets to the dash by way of the ECU? Wondering if there's a corroded pin on there that's blocking the signal?

Fairly sure that the dash itself is OK as it comes up from rest to just under the first denotation, so it does move!

The temperature needle gets its signal from pin 75 or 80 on ECU (depending on year, 75 before 09/2000, 80 after that date for the digital IC). On the same IC the signal for temperature goes in on PIN 19 if I am not mistaken.
All the sensors on Ford operate with 5V. I guess if you tried getting some smallish voltage to that pin the needle should move?
Just thinking out loud...? Hope it helps

I was going to try bridging the connector to the sensor to see if that moves it (just to check the dash isn't at fault).

My thinking with the ECU is that it sits where I had some major water ingress before I plugged the leaks. It was always sopping around that area.

The Arch Bishop said:

[post]347000[/post] I'm not great on electrics, so is there any chance that this sensor gets to the dash by way of the ECU?

Click to expand...

Yep. ECU then operates 'choke', various temperature sensitive ratios and fan speeds, dependant on sensor input.

The Arch Bishop said:

[post]347010[/post] I was going to try bridging the connector to the sensor to see if that moves it

Click to expand...

I seem to recall that with these cars, that if you just unplug the water temp. sensor lead (not with the engine running!) then the ECU's fall back is full speed fan mode. So, you can test like that.

So, problem is apparent over-cooling on temp gauge? Few things come to mind -

#1. Puma temp. gauge is different to most, which have a 11 - 1 o' clock Normal range - the Puma has a much wider 10 - 2 o' clock Normal band. It is possible that in this cold weather that there is actually nothing wrong with your setup (OBDII looking at the actual temps received by the sensor and sent to the ECU would be good ...but you can't do that one)

#2. As so many people mention (almost proudly, for some bizarre reason) that their gauge is always halfway, then it's possible that later Pumas use flat response calibration there (simple software change done on ECU that basically puts the needle in the middle unless it hits the fan, metaphorically).

I say that, because my early Puma only goes up to a third in this weather, then around half or more in normal weather. It's possible that your ECU connections need cleaning?

#3. Old temp sensor can be easily tested with a multimeter on resistance and probe in hot/boiling pan of water. Just look for the change on the meter and the temperature increases. That will tell you if your original one was working (it's possible that it was working, but at the incorrect variable rate, but that's another matter)

#4. Usual advice on over cooling is to change the thermostat - very easy to write on a forum, not so easy in real life, I reckon. Eliminate all other possibilities first, maybe even blank off the radiator with cardboard and running with very frequent stops to check. I recall you changed your thermostat housing couple of years back? I'm reckoning your would have changed the thermostat at the same time.

Damn your OBDII connection! In Live Data mode, I'd figure this one out in 10 minutes.

Just realised. You can't be that far from one another, nor me? East sussex, Hurstpierpoint, Gatwick.

Not that that helps you much right now.

That fact that the gauge moves however when you first turn the key unfortunately doesn't prove anything as mine still moves and nothing is present, which can only suggest it's doing that from power to the instrument panel alone? I would like to get it working again though if anyone thinks that's possible.

Hopefully you can figure it out - the the sensor screw into plastic or alloy originally? And I guess it's a two wire sensor? As far as I know (and I think this has already been mentioned ^^^^) the sensor goes to the ECU then to instrument cluster.

Frank said:

#1. Puma temp. gauge is different to most, which have a 11 - 1 o' clock Normal range - the Puma has a much wider 10 - 2 o' clock Normal band. It is possible that in this cold weather that there is actually nothing wrong with your setup (OBDII looking at the actual temps received by the sensor and sent to the ECU would be good ...but you can't do that one)

#2. As so many people mention (almost proudly, for some bizarre reason) that their gauge is always halfway, then it's possible that later Pumas use flat response calibration there (simple software change done on ECU that basically puts the needle in the middle unless it hits the fan, metaphorically).

I say that, because my early Puma only goes up to a third in this weather, then around half or more in normal weather. It's possible that your ECU connections need cleaning?

#3. Old temp sensor can be easily tested with a multimeter on resistance and probe in hot/boiling pan of water. Just look for the change on the meter and the temperature increases. That will tell you if your original one was working (it's possible that it was working, but at the incorrect variable rate, but that's another matter)

#4. Usual advice on over cooling is to change the thermostat - very easy to write on a forum, not so easy in real life, I reckon. Eliminate all other possibilities first, maybe even blank off the radiator with cardboard and running with very frequent stops to check. I recall you changed your thermostat housing couple of years back? I'm reckoning your would have changed the thermostat at the same time.

Damn your OBDII connection! In Live Data mode, I'd figure this one out in 10 minutes.

Click to expand...

The temp gauge sits below the very bottom, well below the normal range. It moves slightly up to this when the ignition is switched on.

The themostat was changed last year to try and solve this issue and the cooling system is in very good nick. It was flushed at the same time and new pink coolant put in. This was my last gasp effort in terms of parts to change that would affect the gauge.

Interesting regarding the choke status - I've long complained about a lack of general power and a sooty exhaust. It does make me wonder whether this is all part of a larger problem!

moondustka said:

[post]347024[/post] Just realised. You can't be that far from one another, nor me? East sussex, Hurstpierpoint, Gatwick.

Not that that helps you much right now.

That fact that the gauge moves however when you first turn the key unfortunately doesn't prove anything as mine still moves and nothing is present, which can only suggest it's doing that from power to the instrument panel alone? I would like to get it working again though if anyone thinks that's possible.

Hopefully you can figure it out - the the sensor screw into plastic or alloy originally? And I guess it's a two wire sensor? As far as I know (and I think this has already been mentioned ^^^^) the sensor goes to the ECU then to instrument cluster.

Click to expand...

Yep! Not far away at all - 15 mins on the A27!

It's the two wire sensor that sits in an alloy casing attached to the side of the head under the coil pack. If it goes to the ECU, then at least that's the next place to look regarding potentially dodge connections.

Hi Lee
I haven't re-read all the posts again so I might have missed something. It strikes me that either the gauge is not working (or other connections) or the engine is overcooling. Did you run the engine for long enough for the fan to kick in? If you did and the fan kicked in I reckon that clears the temp sensor and the engines cooling system, including thermostat and probably the ECU leaving very little to be at fault.
Barry

I honestly can't remember the fan ever coming on in my ownership. I left the engine to idle on the drive for about 15 mins then went for a short drive.

Does the sensor earth through the head? Someone once told me that I wouldn't be able to get it working on mine because the 2.0 blacktop engines have plastic thermostat housings. I could be barking up the wrong tree but maybe it's not earthing well enough through the housing?

The Arch Bishop said:

[post]347027[/post] Interesting regarding the choke status - I've long complained about a lack of general power and a sooty exhaust. It does make me wonder whether this is all part of a larger problem!

Click to expand...

Hang on....inputting new information........tick, tock...

#1. Bad earth on engine block - run car for 10 minutes. Cut engine. Jumper lead from - ve terminal on battery straight to good earth on block. Ignition on, see if gauge has moved. Simple earthing faults can cause a lot of problems.

If no joy, then -

#2. Check water temp. sensor connection by just removal from sensor and then check gauge with ignition on. Do not bridge the connection without proper checking of relevant wiring diagrams - at the other end of those wires is a very unforgiving ECU.

Anyway, those are a couple of quick elimination steps that spring to mind, but really you need someone who knows these particular engines in detail...

Cheers Frank, definitely worth a go. The strap at the back of the engine looks ok, but looking ok is no guarantee. I'll be taking it to work tomorrow to see if that helps burp the system. After that, it looks like I've got plenty of avenues to explore!

The Arch Bishop said:

[post]347039[/post] Cheers Frank, definitely worth a go.

Click to expand...

No problem.

You've got a good range of symptoms and, troubleshooting-wise, that's great as elimination techniques can be used. Nothing worse than almost no symptoms, apart from an intermittent fault. Cars aren't my area, but the general principles of problem solving are pretty universal tools.

If you get stuck, I'm 95% certain your problem falls under the expertise of an auto electrician. A mobile one charges about £40.

As they say in The Great Escape - 'Good luck'.