Water Temperature Gauge Fault

[so8]

Driving my Griff into work today I watched as the water temperature gauge went from the 80 or so indicated down to almost zero and then up to 60. Down to almost zero again and then back up to 80 as though nothing had happened! It did this twice over about twenty minutes - the engine was running absolutely fine.

Any ideas - loose wire, dodgy sender ? Anyone here had similar ?

[GreenV8S]

The sender is a simple thermister, more resistance corresponds to colder, so I would guess either the sensor or the wiring went open circuit briefly. Check out the condition of the wiring loom by the sender and make sure the connection to the sender is sound. The sender is screwed into the water jacket at the front of the inlet manifold, follow the top hose back to the engine and that will take you to the inlet manifold.

[GJR]

I've had the same intermittent fault since I bought mine. On each service at a TVR main dealer it was mentioned, and on each occasion I was told that the connections and parts had been cleaned/checked and were working fine.... A few days later they'd start plying up again!!!

I was told (on here I think) that it could be a bad earth..??
But, is it likely to be the earth?? thermistor?? wiring?? gauge??... or something else I haven't thought of yet??

G

[Griffit]

My temperature gauge wanders up and down erratically sometimes too. I'll be interested in all of the options posted too as its the next job on the list after I've put the door back together. I'll need to dig out a multimeter from somewhere to test the sensor itself as well as the wiring continuity. Mine only worries me because it gets more erratic once the engine is up to temperature and I'd like to know when I'm closing in on the fans starting to run.

[david beer]

If you have a serp you use the spare sender(if fitted), saves draining water etc. Using a variable resistor you can calibrate it. SO8, you have not done the hot start mod, i see !!!

[Griffit]

Mine's a serp - where would I find the spare sender if it's fitted - presumably its neare the other one? I don't recall a mention of this in the bible but it would be a good way to test whether it is the gauge or sender that is at fault.

[david beer]

It on top of the head, next to the ECU temp sender, it has a single 4mm round connector. Usually a 120 ohm resistor will be right but you are better off with a 200 ohm variable. As this one is in water flow, it doesnt under read on a cold day like the original that is not in water flow, just on the end of an old bit of pipe.

[that daddy]

SO8, my car as done this since i purchased it i know its the sender,just have not got round to doing it,because i know it does it i dont worry,it climbs to around 90 in traffic then drops to 0 once moving when the temp as dropped it registers to normal,then behaves itself,take the others posters opinions there right.

[FlipFlopGriff]

david beer said:

It on top of the head, next to the ECU temp sender, it has a single 4mm round connector. Usually a 120 ohm resistor will be right but you are better off with a 200 ohm variable. As this one is in water flow, it doesnt under read on a cold day like the original that is not in water flow, just on the end of an old bit of pipe.

Another plug and play mod David for us numpty's????
FFG

[david beer]

Only for the last 5 years since my 18 month old Griffs sender began to top out at 70 ! Just plugs in, but iam not allowed to "plug" !, stealth post it is.

[Gremlin500]

Just to add my 2p...
Installed new Leven stainless dash into Gremlin Saturday, got it all in, lots of polish and swearing, thought ooops, better check all instruments are working before lifting steering column up & installing my new Pioneer CD, and guess what? Yup! turned ingnition on, and Temp gauge shot up to 130 deg! Whoa! that's pretty hot for an engine that's not been running for 2 weeks...
So, today dash back out, (More cursing and swearing)checked all wires/connections, all OK compared to digital pics of old dash, just so happened I had spare new otter switch, so plugged it in place of the old one and, bingo! the problem went away. I might add that the resident switch was brand new only 6 months ago. Just so weird that a component can fail even when the car is left unused, I was so sure it would be a wiring problem!

[spend]

Gremlin500 said:

...Temp gauge shot up to 130 deg! ...I had spare new otter switch, so plugged it in place of the old one and, bingo! the problem went away...I was so sure it would be a wiring problem!

I think you may well have had a wiring problem. The otter switch controls the fans, it has nothing directly to do with the temp gauge.

Dave

[Gremlin500]

spend said:

Gremlin500 said:

...Temp gauge shot up to 130 deg! ...I had spare new otter switch, so plugged it in place of the old one and, bingo! the problem went away...I was so sure it would be a wiring problem!

I think you may well have had a wiring problem. The otter switch controls the fans, it has nothing directly to do with the temp gauge.

Dave

Doh! Thanks!-yes, that's right, so why should pulling the wires off the old otter, and plugging them on to a new one (not screwed in) drop the needle back to zero again? I'm confused, could it be an earth fault? Some of the wiring on the car is a knife and fork job, tho'. Car has not moved since engine warm-up 2 weeks ago, and all dash wires are 100% back in the correct place, took it all out of the car, back home, checked each instrument against digital pics before replacing again. May have disturbed something else somewhere, will check all again at the weekend.

Phil

[GreenV8S]

Are you sure the thing you're replacing is definitely the otter switch?

[Gremlin500]

Sorry been away a few days, yes, the 1 with 2 terminals at the bottom of the Swirl tank. Other 1 is mounted horizontally top front of engine, only 1 wire (so why are there 2 wires (+2 black) on the back of the gauge?
(I am not talking about the ECU water temp sender, which screws in vertically and is hidden behind all the little hoses top front of engine)
Does anyone have a proper Pre-Serp Griff wiring diagram? The Bible has one from a 400, and is difficult to read...
Decided to book the car into HHC for some dignostic checks, as the idling problem I had has returned big style, will report back end of next week, thanks Peter.

PhilR

[spend]

Its more than likely just a bad connection (single spade) to the temp sender. The Otter switch shares the sub loom ~ so your 'wiggling' may have affected performance. Just fettle the single spade terminal (prob with green corrosion) on the top front of the engine.

Dave

[so8]

Thanks for the comments people ..... in typical TVR fashion the gauge has performed in faultless manner since I put this post up !

Maybe it didn't like being left unused for a couple of weeks and is now happier things are back to normal ....