My SE6a Over Heating Cure

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spegru
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My SE6a Over Heating Cure

Post by spegru » Tue Jun 19, 2018 9:58 am

Had my car running (not yet driving) for quite a while over the weekend. Please to see rock solid 90 on the gauge but surprised that the fan keeps spinning up over and over. The Thermostatic Otter(?) switch on the radiator is clearly working as the fan is slowing down, but never actually manages to stop, as it's coming every few seconds. Most fan switches have something called hysteresis which means that they switch on at a certain temp but them wont switch off until a much lower temp - which should prevent that
Incidentally my new fan is a multi bladed, ducted affair connected directly to the radiator which works very well but I don't think that is relevant
This is not really a fault but it does seem odd



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My SE6a Over Heating Cure

Post by philhoward » Tue Jun 19, 2018 11:11 am

The latest Otter switches have less hysteresis than the originals (I gather) but as water flow is quite low at tickover, your fan is cooling just the water in the radiator (and quite quickly, at a guess), rather than dropping a larger amount of water over a longer time.

Just a guess - but do you have a new Aluminium radiator per chance?


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Post by spegru » Wed Jun 20, 2018 8:57 am

No it's justa standard one as far as I can tell. Yes it could be just the water in the rad but still a bit surprised



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Post by giddo » Wed Jun 27, 2018 11:53 pm

& BMW ?


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Post by giddo » Thu Jun 28, 2018 1:52 am

It seems to me that this link is relavent to this discussion
http://www.scimitarweb.co.uk/sgwrs/view ... 14#p450914
My GTC has been suffering with overheating problems and so I have been toying with the idea of doing something like justfur has done. My car also has the fan switching on and off and on again in what seems to me to be very quick succession. Since having a new core in the rad -claimed to be 20% more effiecent than the original - I've done around 100 miles and the water is steady at 90-95 deg leaving the engine.

What we dont know is how much cooling capability is in reserve in the system. Remember the thermostat will not allow water colder that its changeover temperature ( 85 / 90 deg or whatever) to enter the engine. The temperature sensor reads the temp of water leaving the engine, so engine heat has to be removed with only a differential of 85 to 95 deg. It is true that we do have a bit more 'elbow room' in that a13psi pressure cap will allow operation up to almost 120deg ( water boils at 100 @ 0 psi ; 115 @ 10psi; 121 @ 15psi [apologies for mixed units] ). So to provide more heat removal capability we must either increase water flow, or increase water temp spread. As an aside here this issue will be very relavent to anyone thinking of tuneing the engine as "heat to cooling water is proportional to BHP produced".

So I think the aeronatical engineers and the motor engineers are both partially right; Ian's variable temperature switch for the fan will allow control of the cooling power of the radiator letting it deliver back to the engine water at a lower temperature. However this needs, in my view, to be complemented by a lower temp thermostat. Remember thermostats were only introduced to cars to improve the thermal effiency of the engine so that they did not run far on cold water. My dad used to put a piece of cardboard in front of the radiator of the old Hillman in winter.

Sorry its been a bit long, and I'm open to comment and correction.


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Post by Dennis Nicholas » Thu Jun 28, 2018 10:51 am

Just a reminder to all....The GTC cologne engine thermostat has two valves. When below opening temperature the main through-the -radiator valve is shut but the extra disc at the bottom .....the second valve ....allows water from the pump to flow in the by-pass hose to the engine so that water is only circulating within the engine. When engine operating temperature is reached and the thermostat opens to allow water to the radiator then the disc at the bottom closes off the by-pass so water is NOT recirculating directly through the engine ..........if that by-pass is not closed off then hot water is pumped round the engine (as well as to the radiator) and over heating can occur........so very important to have the correct thermostat.

Reliant figures are:
Opening commences 84 to 88 C
Fully open 102 C
opening distance 7mm.


A Ford part No 73TF8575 A1A.
Other equivalents:
CALORSTAT BY VERNET TH1439.87J
BEHR TX1387D
BEHR THERMOT-TRONIK 1.130.87
BEHR THERMOT-TRONIK 1.130.87.307
FAE 5303987
MAHLE FILTER TX1387D
You will notice they all have "87" featured in the part number.....I am guessing that refers to start opening temp which is in the range between 84 to 88C.

The Ford Granada manual with Cologne engine shows start open 89 to 93 C and fully open 107 to 108 C (+/- 3 deg for used ones).

Final thought....the cars ran a long time in standard form......mine now done just over 100,000 miles and no overheating ....indicating just under 90 on gauge most of time and slightly over in this hot weather........temp confirmed with laser temp gun and thermocouple on a test meter. Do we really need
extra fans/gismos??......see my previous comment re fan running at end of journey. Rebuild cooling fan with new brushes and re-lubricate/renew the bearings for many more years use.

Dennis


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Post by Dennis Nicholas » Thu Jun 28, 2018 10:59 am

Just in case anyone did not understand the reference to aircraft engineers having nothing to do with motor cars......Bristol built some very good vehicles as well as their fine aircraft.....also the other manufacturers mentioned.

Jim has a very long successful history with Reliant Scimitars rebuilding/helping others rebuild and fault finding.

Dennis


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Post by scimitargtc » Thu Jun 28, 2018 11:55 am

Quickie. I want to “heatproof” my 6a auto ready for the road after 4 years and wish to reinstate the mech water pump in addition to the Craig Davies electric pump but cannot for the life of me remember how to plumb what to where. The existing pump spins freely and wasn’t leaking before I added the electric pump years ago. Can’t see it n the workshop manual and would gratefully receive a drawing or photo tia :D


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