AC Owners Club Forum
AC Owners Club Forum => Mk IV, Superblower, CRS and other Continuation Cars Forum => Topic started by: nick Godridge on September 24, 2012, 11:35:44
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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The std top hose filler has been replaced by an inner wing mounted header tank linked to both top and bottom hoses.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.
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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.
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Images posted by Nick Godridge.
(http://i616.photobucket.com/albums/tt244/ak1023/No_zps0d3c9495.jpg)
(http://i616.photobucket.com/albums/tt244/ak1023/No2_zps54461515.jpg)
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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.
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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
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Thx also to Chobham Cobra. had'nt considered the rad sender. I have replaced the thermostat with a Stant superstat.
Nick G
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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
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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.
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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
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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!
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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° ...
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That makes sense. I guess the car never cools down such that the fan kicks off.
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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.
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BTW, i'm still looking for the origin & reference of the push-in thermoswitch [:I] ...
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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!
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You could have the issue where the fan & the `stat are fighting each other, rather than working together, so maybe worth considering!
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@BBK: I can't see the sense of switching thermostat ! neither to remove it, as I've often seen on british cars that I've bought in the past ...
regarding the thermostatic switch, I found on Club Cobra website that the Lucas SNB748 may fit our radiator, and it looks so :
(http://cdn.media.oscaro.com/jpg/zoom/240/36080.jpg)
I'll order one and let you know...
PS: BBK, you can see on this picture the cutting in/cutting off temperatures [;)]...
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One thing to check is the location of your fan thermo switch .
My CRS (Stroked 302 non standard) has it on the highest point of the engine (not on radiator)in the metal heater hoses right above the water pump. Not ideal as this area will allways be the hottest part of the system,and explains why my fan runs on a lot when I stop. Saying that its also close to where the gauge temperature sensor is mounted.
Some schools of thought say wire in your fan to a dashboard switch and junk the automatic system.
Another CRS (and MkIV?) thing to watch is airlocks. The bleed on the top of my CRS radiator did not run back to the expansion tank-so I fitted a long rubber hose that I can vent to air then block off. The MKIv engine bays I have seen show a bleed hose back to an expansion tank.
A lot of the aftermarket kits have a thermo couple that slips under the radiator top hose and an adjustable setting.
Incidentally I run a milodon full flow thermostat that I got from performance unlimited.
http://www.summitracing.com/search/Brand/Milodon/Product-Line/Milodon-High-Flow-Thermostats/
One other thing to consider is that in an effort to fix "so called " running hot problems,your timing may have been adjusted in the past (more advance dialed in),so thats worth checking. (Retarded ignition timing causes overheating)
I concluded that the installed gauge & sensor are relative junk-crudely calibrated at the 90degc point(20DEGC INCREMENTS?) ,all electrical so placing ones faith in this as gospel is foolhardy. I also bought an infrared gun (Fluke) and it confirmed that my gauge is showing about 10 degc to hot. (And it measures AGA temperatures!)
Graham
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quote:
Originally posted by French Frie
@BBK: I can't see the sense of switching thermostat ! neither to remove it, as I've often seen on british cars that I've bought in the past ...
regarding the thermostatic switch, I found on Club Cobra website that the Lucas SNB748 may fit our radiator, and it looks so :
(http://cdn.media.oscaro.com/jpg/zoom/240/36080.jpg)
I'll order one and let you know...
Thanks for the information!!
PS: BBK, you can see on this picture the cutting in/cutting off temperatures [;)]...