Heat Soak cooling time request.

[DMT]

Evening Folks

I am soon fitting a cooling fan as a back up which I will have running off a fused permanent supply. I will keep the mechanical fan and plan to have the electric fan coming on only above normal running temperature. I assume if the system is very hot, it will run on after the ignition is turned off, but I assume as it is switched from the top hose sensor it will not run on too long.

My problem is when I do short 4 ish mile trips to the shops the water has not reached normal temp but the exhaust manifolds have got very hot and 15 mins later when I try to start her she is a bit reluctant to start.

I plan to have a push button that sets a timer to run the fan for a predetermined time to get rid of the hot air around the carb.

My question is how long do you think I should run the fan? I am thinking 2 mins.

Any ideas would be gratefully noted.

Dave

[singapore stag]

Get an Infra-red thermo (they are cheap) get a before and after reading in several places. Get an idea of the temp........then switch off and take several readings of temp. Thats what I done to set my fan.

[DMT]

Cheers Sukhi, I already have a thermo, just not thought to us it.

[StagJonno]

Sounds reasonable, though if you've an option of up to 3 min it might be useful.

I'm going by my experience with the Davies Craig EEWP, which is not quite the same as the DC controller keeps both fan and water pump going for up to 3 min from switch-off or until the water temp reduces to 10C below the set point (which is near enough the target running temp). It has usually got to a low enough temperature within a couple of minutes. Lifting the bonnet at that point, there's no wave of heat coming off the engine/ exhaust manifolds.

[DMT]

Thanks Jonno, I have ON or OFF delays from 0.5 sec to 6 hrs. I would have guessed 2 to 3 mins would seem OK pulling 20A. I am thinking of having the Fan running from the ignition supply from the sensor and direct from a fused battery supply from the timer.

I must admit I do like the idea of the fan running after the ignition is off as per the modern cars. I would expect they are on some sort of timer or monitor to stop battery draining.

[jbuckl]

My electric fan does this. 12v supply is from battery fused. The thermocouple is on the fuel pipe. It has been set as low as 40 degrees C. But now 55 degrees c.
on a hot day (32 degC) it took 6 cycles & 30 odd minutes to stop operating the fan.
it did not drain the battery, helped with hot fuel handling
started fine.
hope that helps.
the fuel circuit is also currently & securely modified to take a bleed return to the tank.
fuel supply line is all non metal / pvc / nylon from pump to filter & has silicone fibreglass heat shielding. l/h exhaust silencer has a heat shield as supplied, but less reach than was supplied on original mild steel system. ( some don’t have a heat shield at all !)
Fwiw the above wouldn’t be necessary if:- 1 fuel didn’t boil at 36 degrees c
2 our float valves shut off properly…. Have tried all types available…. ( cheap, viton , grose ) Currently on zenith kit type & 1.9 psi fuel pressure.
IIRC floats are set to 17mm.

[DMT]

My electric fan does this. 12v supply is from battery fused. The thermocouple is on the fuel pipe. It has been set as low as 40 degrees C. But now 55 degrees c.
on a hot day (32 degC) it took 6 cycles & 30 odd minutes to stop operating the fan.
it did not drain the battery, helped with hot fuel handling
started fine.
hope that helps.
the fuel circuit is also currently & securely modified to take a bleed return to the tank.
fuel supply line is all non metal / pvc / nylon from pump to filter & has silicone fibreglass heat shielding. l/h exhaust silencer has a heat shield as supplied, but less reach than was supplied on original mild steel system. ( some don’t have a heat shield at all !)
Fwiw the above wouldn’t be necessary if:- 1 fuel didn’t boil at 36 degrees c
2 our float valves shut off properly…. Have tried all types available…. ( cheap, viton , grose ) Currently on zenith kit type & 1.9 psi fuel pressure.
IIRC floats are set to 17mm.

Wow, cheers. I will start with a battery feed and monitor the situation. Thanks for the help.

Dave

[trunt]

I have the Davies Craig and the 3 min/10 degree it does seems fine, no issues even on 100deg f days after a hard drive, I have no mechanical fan.

[Wheelz]

Wow, cheers. I will start with a battery feed and monitor the situation. Thanks for the help.

Dave

If you have a Weber 38 carb there is an 8mm fuel hose outlet which can be connected directly back to the fuel tank. This helps cool the fuel, and also prevents any fuel pressure build up which causes flooding.

[DMT]

If you have a Weber 38 carb there is an 8mm fuel hose outlet which can be connected directly back to the fuel tank. This helps cool the fuel, and also prevents any fuel pressure build up which causes flooding.

Cheers, I hadn't thought of that. I use this port as the pressure reading to set up the regulator in the boot.

Is it just a pipe connection from the port to the tank?

[RNF]

Couldn't you use a phenolic carb spacer or if you have no clearance you could cover the float bowl in heat resistant tape or possibly make a heat shield to protect the float bowl?
Get all McLaren-like and use the gold tape. https://www.amazon.com/dp/B0039Z5TRC...ing=UTF8&psc=1

[DMT]

The carb comes with a insulating lower spacer about 5mm thick, I believe most of the heat is in the stationary hot air surrounding the carb and fuel pipes mainly from the exhaust manifolds.

I have shielded the fuel pipe in an insulated sleeve.

My theory is to remove the heat with the fan.

[Wheelz]

Cheers, I hadn't thought of that. I use this port as the pressure reading to set up the regulator in the boot.

Is it just a pipe connection from the port to the tank?

Yes, thats all you need as there is a restrictor jet already inside.