Possible temp sensor problem

[dave_p]

Hi Guys

I fitted a new otter switch to my 99 T Chim 500 last weekend and since then the fans have been cutting in at 80 DegC I thought I had a lower rated otter switch but on inspection it is a 95/86 DegC which I believe cuts the fans in at 95 DegC and switches off at 86 DegC. I thought that it may be a faulty one, so I tried another with the same rating 95/86 and still the fans are cutting in at 80 DegC according the the temp gauge! Is it possible it could be a faulty temp sensor? if so what is the easiest way to test the sensor? or could it be the temp gauge at fault??

Anyone had the same problem? any advise would be a good help.

Cheers
Dave

>>> Edited by dave_p on Tuesday 17th February 12:53

[mongoose]

hi dave.this is very normal behavior.the problem is that the otter switch is located on the swirlpot,and hence is on the outlet side from the engine.so the water is oviosly hotter than when it went into the engine,which is the side that your temp gauge sender is on.hence there is a difference in that your not comparing temps in the same place.its technically wrong to have the otter switch on the outlet,and nearly all other manufacturers will have there fan switch on or near the rad outlet.i think its nice for the fans to cut in at about 85-90ish btw.trouble is the point at which the fans cut in will never be consistent due to otter location,ie mine cut in around 70 at the mo,but in summer itll be ok.best remedy is to have a rad specialist tap a thread for the otter on the outlet of the rad,or buy a hose insert with variable temp switch fitted from demon tweaks(from £40) and fit it in the outlet hose.cheers,mv

[dave_p]

Hi mongoose

Thanks for the reply.

The otter switch on mine is located on the radiator (passenger side) just below the inlet pipe. Should this make any difference? before I changed the otter switch the fans cut in about 90 DegC ish.

I know what you mean for summer driving it's perfect but I have also just bought the 2 stage cooling system from Mod-wise so I am now wondering what to set the fans to cut in on the control box. I think the guy bases it on the fans cutting in at around 90 DegC.

Any ideas?

Cheers
Dave

>> Edited by Big Al. on Tuesday 17th February 20:37

[mongoose]

i also have this otter switch location,as i had my rad replaced,and now have the later type.its basically the same problem though,as the coolant has yet to go through the rad and be cooled before the switch senses its temp.id leave it how youve got it at the mo,then follow its progress as the climate changes towards summer.the discrepancy you describe sounds right from my experience.

[dave_p]

mongoose said:

i also have this otter switch location,as i had my rad replaced,and now have the later type.its basically the same problem though,as the coolant has yet to go through the rad and be cooled before the switch senses its temp.id leave it how youve got it at the mo,then follow its progress as the climate changes towards summer.the discrepancy you describe sounds right from my experience.

Cool thanks for the advice!

Any ideas on what I should do with the 2 stage cooling system? ie what temp to set the controls for the fans?

Dave

[david beer]

Not sure if iam allowed to comment, i guess i will be binned if not. The new sensors(adjustable) are now on the outlet of the rad, try 70 for the half speed and 80 for the full speed.Of course these temps are after the rad so are not engine temp. The temp sender is on the output from the engine though,as was your otter, they do go and usually show a low reading before giving up.

[dave_p]

david beer said:

Not sure if iam allowed to comment, i guess i will be binned if not. The new sensors(adjustable) are now on the outlet of the rad, try 70 for the half speed and 80 for the full speed.Of course these temps are after the rad so are not engine temp. The temp sender is on the output from the engine though,as was your otter, they do go and usually show a low reading before giving up.

Thanks David

Will be installing this weekend!

Cheers
Dave

>> Edited by Big Al. on Tuesday 17th February 20:38

[mongoose]

david beer said:

The temp sender is on the output from the engine though,as was your otter,

im surprised at that.i was told that the sender is situated just after the pump and is therefore before the coolant has travelled around the engine.visually this looks correct so now im about that part.sorry david,but i didnt realise your kit came with alternatively situated temp.sensors,and didnt get much of a clue with dave changing the otter switch.the kit sounds like a great improvement,the way it should have been done in the first place

>> Edited by mongoose on Tuesday 17th February 20:13

[dave_p]

the kit sounds like a great improvement,the way it should have been done in the first place

Totally agree!

cheers

[wrinkly]

Is a hotter otter notta lotta good then?

[david beer]

Over my glass of madicinal wine, just a thought.If you have drained the system to replace the good old" rotter otter", you may of not cleared any airlocks,so the the temp sender(at the end of a bit of old pipe)may be in an airlock and reading low.
Edit. the sender is positioned just before the water is let out of the thermostat area, but it is not directly in the flowing water. Much better to use the Range Rover sender on a serp, its the spare sender on top of the block, a resistor to calibrate and you will no longer see "my car runs at 50 in winter".

>> Edited by david beer on Tuesday 17th February 21:24

[Ballistic Banana]

david beer said:

Not sure if i am allowed to comment, i guess i will be binned if not.

David why would you be worried about commenting..
Your Upgrades/Mods have been most helpful to many a Owner(including Me) and we are always thankful to hear from you and your Knowledge of TVR electrics, coz we all know what they are like..

Regards

Simon

[mongoose]

david beer said:

Edit. the sender is positioned just before the water is let out of the thermostat area, but it is not directly in the flowing water. Much better to use the Range Rover sender on a serp, its the spare sender on top of the block, a resistor to calibrate and you will no longer see "my car runs at 50 in winter".

aha,now where really getting somewhere,both my tivs have been serp engines,so the sender is poorly located on serps.first question:my car does run at 50-60 in winter,as did my last one,but why is it then ok in summer? i dont understand how it can change in accuracy from winter to summer?Q2:how do i convert then please? is it a trial and error thing with the resistor?how do you know the exact water temp to set the gague by,is it just remove the sensor and insert thermometer for comparison?all words of wisdom greatly appreciated,cheers-mike.

[Ballistic Banana]

Mike I set mine when the Fans come on I looked at the guage. I turned the adjustable resistor (That is where David suggested put it) until I had The correct reading on the guage with the Fans On/OFF.
The other way is to put a seperate Temp sensor Around a pipe somewhere and then Calibrate your Guage via the Adjustable resistor with this other Temp Sensor.

Hope that made sense

Simon

[shpub]

Has been known for otter switches to

1. Be marked incorrectly.
2. Go wrong and not come on at the appropriate temps.

I would chcek the otter switch externally with a meter and hot water. If everything else was fine before you changed the switch... then I would be very suspicious of the switch. Failing that, it could simply be that changing the switch has bled some air out of the system so that the otter switch is now fully immersed and while working correctly is switching at a lower indicated temp. As many give their right arms for this lower temp, I would not necessarily worry.

[dave_p]

As many give their right arms for this lower temp, I would not necessarily worry.

Steve

I have bought two new otter switches last weekend marked as 95/86 DegC from Christopher Neils (Northwhich) and both otters cut the fans in at 80DegC..How fortunate is that? Think I might do the lottery this weekend..is it a rollover?????

[david beer]

Mike
if you use a variable as BB said, you can just twiddle until its correct.A 120 ohm seems about right, i have a couple kicking around. The winter summer thing must only be the cold air cooling the pipe that the sender sits in, if you take a look its about 4cm long. Alternatively, wrap it in a nice little jacket. My Griff is virtually the same as the Rangie now.

[mongoose]

david beer said:

Mike if you use a variable as BB said, you can just twiddle until its correct.A 120 ohm seems about right, i have a couple kicking around. The winter summer thing must only be the cold air cooling the pipe that the sender sits in, if you take a look its about 4cm long. Alternatively, wrap it in a nice little jacket. My Griff is virtually the same as the Rangie now.

cheers david,ill try the jacket first,sounds like a good idea.if i end up down the variable resistor route,im assuming you put it behind the dash to avoid the affects of the engine heat?

[david beer]

Its fine in the engine bay, on the new sender, its ok for something like 125c. Its very quiet on this subject, we must be the only few with concerns. I also set up my oil pressure guage as it used to read minus 10, ignition on, before starting. So when started it was reading low,ok "it aint exactly broke" but if you have something not quite right and you can do it, i say do it.

[mongoose]

david,can i just ask one more question please?what did you make your 'jacket out of? this heat sheilding sheet stuff costs £30ish,which seems a little ott considering what ill use.that metal tape stuff any good or is there something else?-cheers,mike.