Mk 1V cooling problem

[nick Godridge]

The temperature gauge on my MK 1V is giving wildly variable readings, which make driving a tense experience.
   
   Some background facts;-
   
   The car is not losing water.
   The std top hose filler has been replaced by an inner wing mounted header tank linked to both top and bottom hoses.
   I have put an electric fan 182 deg water temp sensor in the bottom of the top hose near the radiator joint.
   I have put tell tale strips on top of the top hose near the thermostat housing, on the bottom of the top hose near its entry point to the radiator, and on the radiator next to the temp sender. The one by the thermostat housing shows the highest temp at 87 deg. 84 deg at the top hose near rad.
   The water seems to be circulating properly with top and bottom hoses getting hot and warm respectively.
   
   However, the gauge seems to have a life of its own, which is very disconcerting.
   Sometimes it settles down for a while around 82 deg sometimes in the 90's.  Quite often it will quickly move from mid 80's up to around 100, and back, sometimes settling back to a different temp than its start point.
   
   The fan cuts in, I have to assume at around the correct temp, because of what the tell tales suggest.
   
   Has anybody out there suffered similar issues, and if so what is the fix?
   
   I am currently leaning towards replacing the gauge, but as it is inaccessible behind the centre console, is not something I look forward to attempting.
   
   Please let me know your suggestions.

[linklaw]

I had a similar problem and corrected it by replacing the voltage stabilizer. The gauge needs a relatively constant voltage to function properly and when the stabilizer goes bad, the voltage fluctuates too much and causes erratic readings. This drove me crazy as I thought the car was always overheating. I replaced the stabilizer with a solid state unit and the problem was resolved.

[REV]

Images posted by Nick Godridge.
   
   
   
   
   
   
   
   

[cobham cobra]

Hi Nick,
   My thoughts would be to replace the sender unit before you pull the gauge out of the dash. Also check and possibly replace the thermostat. FYI – the chaps at Thunder Road fitted an adjustable temperature switch in line to the cooling fan on my car which allows me to fine tune when the fan kicks in. I think they have new ideas for an automated switch and will check with them and update this thread next time I visit. FYI – before my MkIV I had a 5 litre TVR Chimaera which can be far more marginal regarding engine cooling. I had that car fitted with a two stage switch which helped keep temperatures in line.
   
   http://www.chimaerapages.com/resources_fan.php
   
   John.

[nick Godridge]

Thx REV, your comments appreciated.
   Is replacing the VS something I could do?  that is, do I need to be an auto electrician or is it a bolt on replacement?
   
   Nick G

[nick Godridge]

Thx also to Chobham Cobra. had'nt considered the rad sender. I have replaced the thermostat with a Stant superstat.
   
   Nick G

[REV]

If the fan is not cutting in all the time and your strips are not showing high temperature then all appears well.
   
   I'd try the sender first as it's an easier and cheaper option.
   
   As John says guage out should be the last resort.
   
   Replacing should be fairly straight forward, but I personally would get someone to do it for me. I always find it easier and more reassuring if a pro does it!
   
   Fingers crossed for you.
   
   Nick

[SB7019]

Thunder Road also fitted an adjustable rad sender to my car which works fine.  Sat in stationary traffics for 1 hour last week with no problems whatsoever.

[nick Godridge]

Thankyou to those who sent responses to this post and my post about dashboard removal.
   
   Erratic temperature readings turned out to be a loose earth contact at rear of the gauge.
   
   Nick G

[BBK]

While we are on the topic of fans and cooling, a few months ago when my Mk IV was in the shop, I had the radiator removed and rodded out.  The car's temperature reading is pretty much spot on now at 90 degrees C, even on the hottest days (it was running hotter than this prior to the radiator work).  The fan kicks in when it reaches 90 degrees.  However, the fan stays on once it reaches that temperature and never turns off.  This would be expected with around town driving, but on the freeway when it is cooler such as it is now, with lots of air flow into the radiator, the fan does not turn off.  I have noted that the temperature on the gauge (while driving with good air flow into the radiator) reads a touch less than 90 degrees in this cooler weather.  Is it normal for Mk IVs to have the fan stay on at all times once it reaches the initial operating temp, or should it kick off once there is good air flow and the operating temp seems to back off a bit from 90 degrees?  My concern is that with the fan running all the time that it will impact the life of the fan motor.  I would hate to have it burn out prematurely!

[French Frie]

Usually, the thermoswitches have two temperatures marked on them : one for the cutting in (say 90°c), and one for the cutting off, which is lower (let's say 82°c)... So, in your case, it seems logical that it doesn't cut off if the gauge needle is  only just before 90° ...

[BBK]

That makes sense.  I guess the car never cools down such that the fan kicks off.

[French Frie]

No, especially if the weather is warm out there ! My problem is that my fan cuts in too early, and as the temperatures are low those days (<10°c), the engine temp never rises higher than 70/75°, which is not a good thing ... I checked with an IR thermometer, and the gauge seems to be accurate.

[French Frie]

BTW, i'm still looking for the origin & reference of the push-in thermoswitch [:I] ...

[BBK]

quote:Originally posted by French Frie
   
No, especially if the weather is warm out there ! My problem is that my fan cuts in too early, and as the temperatures are low those days (<10°c), the engine temp never rises higher than 70/75°, which is not a good thing ... I checked with an IR thermometer, and the gauge seems to be accurate.
   

   
   Does it make sense to switch to a different thermostat in the cooler months where the car will run warmer?  Probably a bit of a hassle though!