Standard engine thermostat temperature & other Q's.

[TomLS]

Hi all, been a while since I was here!

I will be replacing the mechanical fan with an electric one (I know the arguments, but I have decided...)

I can get thermostatic switches with varying hystereses, for various temperatures. I have read that in a road car, the optimum operating temperature for the A-series is 85-90DegC. Does this mean I need a thermostat with the on-off temperatures of 90-85, or would 90-80 be safer for hot days?
Is there a significant thermocline between the block and the top radiator hose? (where the switch will be located). If so, then a thermostat of 85-80 or 85-75 might be more suitable?

I will be fitting an "On-Off-On" toggle switch and a parallel LED to the circuit, so that the fans can still be used in the event that the thermostat fails.

[mike.perry]

A simple engine needs simple answers. What do you hope to achieve with the extra technology?

[chrisryder]

The standard engine thermostat is 88 degrees if i remember rightly.

I have a Kenlowe electric fan on my minor, which is conveniently adjustable to ensure it comes on at the desired time. According to the kenlowe paperwork, the fan shouldn't need to come on whilst driving at normal speeds, just when in slow moving traffic on hots days, or when stationary for prolonged periods of time. I've no idea what temperature it's actually coming on, as the adjuster is just a 1-10, and my temp gauge on the dash is just a H-C.

In conjunction with a gauge on my dash it was easy to set the activation point and see if the fan was coming on too early or too late. I can now sit in traffic and watch the gauge creep up so that the needle just passes the N and then the fan kicks in and it creeps back down again.

My minor is also set up so that the redundant light on the speedo (change oil filter light) comes on when the fan is running. I also have an extra switch on the dash (the same as a windscreen wiper switch) to over-ride the thermostat in the event of its failure, or if i think the fan should come on and it hasn't yet.

It's also worth considering how you mount the fan, and how easy it is to remove. If the fan is fixed semi-permanently to the rad, then it's worth cutting the wires and putting spades or bullets on so that you can unplug it easily if you need to remove the rad, or the whole front panel. (which i seem to do quite often...)

This paragraph is more for Mike's benefit than yours Tom: The lack of an engine driven fan on my minor has meant that the engine warms up much faster, especially notable in winter months where the temp gauge is up to 'Normal' within 2 miles, rather than 4 or 5 before i converted. It's also notably quieter with less noise being generated by the fan blades. i'd also imagine it's more powerful and more economical, but i've got no quantifiable results on that front.

The only real downside i've found with the fan is the draw in places on the battery. In traffic, in the dark, in the rain, when you've got wipers going, lights on, and you've been stationary long enough for the fan to come on, my voltage gauge does tend to plummit rapidly... often causing me to have to increase the engine revs to get it charging.

[bmcecosse]

I always ran my Minor (and Mini) without the fan (but without electric) - indeed quieter, although the warm up time stayed the same - with a working thermostat- why would it improve ?? I would set the fan to only run just before the engine boils - so 95 degrees - something like that. And assume hot water rises - so top hose should be fine.

[chrisryder]

I always ran my Minor (and Mini) without the fan (but without electric) - indeed quieter, although the warm up time stayed the same - with a working thermostat- why would it improve ?? I would set the fan to only run just before the engine boils - so 95 degrees - something like that. And assume hot water rises - so top hose should be fine.

surely the engine driven fan is cooling the engine before it gets up to temp. and that's the benefit. an electric fan only cools when it's needed. the engine driven fan is always turning, always cooling, always drawing power from the engine, and always noisy!

[bmcecosse]

The thermostat should be closed - hence no water should flow to the radiator. Of course - there will be 'windage' from the fan over the engine - but hardly significant cooling from that. Only problem I had with my present car was that I presented it for MOT - they started it, put it up on the ramp and left it idling there for nearly an hour, with no fan...... Next day - it blew the head gasket on me. Obviously it had a good 'roasting'........

[Alec]

Hello Tom,

be aware that the temperature marked on the thermostat is it's opening temperature and fully open is about 8 to 10 degrees higher.

Alec

[MikeNash]

Couple of thoughts, Tom. If you're running the usual 4 psi pressure radiator cap then boiling is raised to about 105C (I don't have steam ables at hand but that's about right.) So you've more "head room" than you might think. Secondly, I think Alec's wrong; in my experience thermostats open fully over only 2-3 degrees above their nominal value.
And, for interest, I run an 89C successfully on an unmodified 1098 with its original 1963 radiator winter and summer even at full bore with a trailer and rarely exceed 95C. Regards, MikeN.

[Alec]

Hello Mike,

the figures I quote are from my workshop manual, not aguess.

Alec

[MikeNash]

Hmm. They probably vary, then. I've tried them in a saucepan with a good mercury thermometer and I've usually seen them open v quickly. Am away for a while but later I'll give it another go to check and see if I remember right and get a more accurate fix, MikeN.

[TomLS]

Thanks for all the replies folks!

Based on the given information then, I am leaning towards Intermotor Part # 50240, which comes on a 90deg, and switches off at 80deg. I have recently replaced the radiator cap, and the temperature shouldn't go much above 95.
I am tempted to go a bit cooler, but I think I will appreciate the few extra degrees when I'm stuck in traffic in the winter! (If it can even get that hot).
I also managed to pick up some cheap exhaust heat wrap, which will hopefully help to keep the temperature under the bonnet down.

[MikeNash]

Did some checks and Alec is right about the temp rise needed to get full opening.
Two thermostasts were slowly heated in a pan on the stove and watched closely. Obviously its too hot to measure openings directly so the gap was compared visually with a ruler held as close as possible. Both cracked open at their nominal opening temps but needed quite a rise for full opening. This is what I saw;

82C stat at 84C 87 89 90 92 95 98
opened (mm) 1 2 3 4 6 8 9

89C stat at 91C 92 94 95 96 97
opened (mm) 1 2 3 3 4 5

As the pan colled both stats fully closed at their nominal temperatures.

Regards, MikeN.

[MikeNash]

Sorry about the lack of proper spacing on the opening measurements above. They're right on the layout when I put in the new post but bunch up after I submit it. If I did it in Word and pasted it in would it make it better?
Regards, MikeN.

[bmcecosse]

It would - but it's perfectly understandable as it is. These readings show the stats to be remarkably accurate. A switch that doesn't go off until 80C will likely never switch off once it goes on. Why bother ? Just put a manual switch and flick it on in heavy traffic - you won't need it any other time.. ...

[linearaudio]

I'm with the Flying Scotsman on this one! Having put a much smaller capacity Metro radiator on, with its associated thermostatic fan, the temperature gauge still never gets over 80 this time of the year, even with half the rad blocked off with cardboard, and the fan has only ever switched on VERY occasionally in summer when caught in stationary traffic for more than about 5 minutes. Use a simple switch- if you are stuck in a traffic jam in summer, you will know to switch the fan on!The engine DOES warm up more quickly with a switchable fan- possibly just slightly attributable to the fact that a fixed fan will have an unavoidable throughput of cold air which will be fighting the engine, carb & exhaust manifolds efforts to warm up, and from what I vaguely remember from history, the fan will work best at a particular speed, such as when most needed, such as at slow speeds (traffic situations), so the good old school run/down to the shops is when it will be working hardest against the thermodynamics of the internal combustion engine.
And I am going to ditch my "big W" brakes as soon as I can sort some discs out, for the exact opposite reason- they heat saturate when you most need them, in an unexpected stop from 70ish

[bmcecosse]

You must have rubbish linings in them LA - I've never had the slightest suggestion of fade despite some hefty stops and long downhill runs at fair speed!