Fan Control Change

[UKPhilTR7]

Over the weekend I replaced the fan controller on my 2lt 7. The on that I had on was going as there was a bad connection and sometimes the fan came on and then sometimes it would not until I moved the cables on it. So I thought it time to change it.

I got one of the Revotec controllers that came with a new relay, so replaced all the old with the new. All went OK, but I previously has two cables going to to the fan, but now I have one. That is OK as they boch did the same thing when a power supply was connected.

So, new controller in (not much coolant lost) as on the top hose, all wired up and the car running up to temperature. Previously on the old fan controller the fan would kick in at half on the gauge and stay on until the original gauge needle went to 1/4.

So when setting the new controller up, I waited till the gauge got to 1/2 and was about to turn the fan on. However, then (as the expansion tank cap was off) she started boiling out of the tank and going out of the overflow pipe.

Was this just due to the fact that the cap was off or was there something more serious going on? I do not think it was a bubble as did not empty her out.

I am replacing the gauge sensor and the thermostat, change things over before I put new coolant in.

I am going to flush her but was wondering what position on your dash temp gauge your car runs at? Mine is just standing still at the moment, but if she was running with the air flowing through, would you expect her not to go past 1/4 on the gauge?

[saabfast]

Is the fan controller not adjustable?
I changed to an electric fan when the original got noisy. I have the controller set so that it comes on at just below half on the gauge and switches off at just above 1/4. (With the original fan it always ran at between 1/4 and 1/2, mainly just above 1/4 unless in heavy traffic congestion on a hot day).
You system could be boiling due to not having the rad cap on as the cap allows the system to pressurise and run hotter without boiling (ie raises the boiling point). You do still need to go through squeezing the top hoses prior to putting the cap on though to get all air out of the system.

[Hasbeen]

I don't believe the tank fitted to the 7 is an expansion tank, I believe it is a simple remote header tank.

I never liked the fact that my 7s water level stabilised at about 2.5" below the filler cap, as this is below the highest point of the cooling system. When we retired a Toyota Cressida I fitted it's expansion tank to the 7. It fits perfectly beside the radiator on the inner guard, filling the gap previously somewhat closed by a waxed cardboard panel.

With a redrawing radiator cap the level has now stabilised at less than an inch below the filler cap. The car has not ever required a coolant top up since I fitted this, other than at a couple of coolant changes over the last 5 years.

Hasbeen

[FI Spyder]

Whatever it's called the difference between when the system is hot such that expanded coolant flows out of the overflow tube and when the system is cool and the contracted coolant is below the point where the low sensor turns on the light on the dash (1980 and later) isn't very much. I do get a warning sign however as when I go up my steep driveway the low coolant light will turn on and then go out when I am horizontal again. Where the temperature needle should sit is like asking how long is a piece of string. As the gauge is analogue, it depends on the resistance in the circuit and other things. Any poor/bad connections in the circuit, from where it gets the 12V current to where it grounds it to complete the circuit, will raise the resistance. Depends on the characteristics of the particular heat sensor, same with the gauge, The voltage of the system (alternator, etc.).

[dursleyman]

I have a Revotec on mine and set it to come on just below half way on the gauge. It usually runs at just over the quarter mark.

[busheytrader]

Where the temperature needle should sit is like asking how long is a piece of string. As the gauge is analogue, it depends on the resistance in the circuit and other things. Any poor/bad connections in the circuit, from where it gets the 12V current to where it grounds it to complete the circuit, will raise the resistance.

Agreed. I removed the capillary adjustable fan controller on mine and replaced it with a fixed temperature on / off switch screwed in to an in-line housing. 95c on and 85c off electric fan control, combined with a 82c coolant thermostat, an aluminium radiator and a new coolant sensor. It’s a V8.

Instead of looking at the gauge for the temperature, I calibrated the gauge from the thermostat’s opening point and the electric fan’s activation. At a steady 40mph on a cold day the gauge holds steady around the 1/4 mark (82c). At about the needle’s width from touching halfway, the electric fan is switched on (95c). If idling whilst stationery, it can take about 60 to 90 seconds for the temperature to fall to the switched off temperature (85c), at about a needles width off the 1/4 mark.

I changed to a fixed temperature switch as I was fed up with the hose weeping around the previous capillary tube. Today’s thinner walled radiator hoses don’t seal as well around it.

[stevie_a]

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.For years I had an adjustable thermostat with the gauge (aftermarket not TR7) needle sat half way fan came on just a needle width over half and off a needle width before half.

TimePhoto_20190512_125530.a76ef047d8d24c03823acdf41c4ee7c8.jpg (79.25 KiB) Viewed 4688 times

But when I put a brand new old stock dash in and decided to change to a fixed 95c on and 85c off and attached it to the radiator.

20210409_105316.jpg (140.1 KiB) Viewed 4688 times

Now the needle sits either side of the quarter.
I would love it sit half way again.
Is there a way to adjust the gauge?

[saabfast]

Have you tried changing the gauge sender to see if that makes a difference?

Mine almost failed altogether and was getting dodgy and erratic so I changed it and it was back to running with the needle between quarter and half as most originals seem to be. When I changed to an electric fan with capillary sensor (adjustable) I set it to switch on at just under the half and it switches off at just over the quarter. I have never checked the actual temperatures but just replicated as close as possible the original running temperatures.

[stevie_a]

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Yes i have actually tried 3 different ones

[Beans]

Did you measure the actual temperatures?

[Hasbeen]

In normal running, hot day/cold day, [33C/15C] Air conditioning on or off, my 7 sits at a needle width above 1/4.

This is with everything stock, radiator, fan, water pump & thermostat but all new 5 years ago when the engine was rebuilt. The only non stock feature is the overflow bottle, which keeps the coolant about 2" higher in the header tank than without it.

That reading is given when the top of the radiator reads 89C on my infer red hand held temp gauge. I can only assume it is the thermostat controlling the system, as it should if the system is adequate & in good condition.

The 4.6L 8 had really bad problems in heavy traffic, despite a big 4 core alloy radiator big fans front & rear of the radiator & all the rest. No problem when being driver really hard, or out in the country cruising.

Finally traced to running very lean at low throttle openings at low revs. It was perfect up top end as tuned on a dyno. With the mixture tuning fixed, no further trouble.

Hasbeen