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MG TD TF 1500 - TF Radiator Cooling

My TF has a brand new, high efficiency radiator and 80w electric fan, controlled by a thermostat in the top tank. The water temp stays at a constant 85 and the fan never comes on whilst driving. However, park the car after a run and within three minutes the fan switches on. I know this isn't an issue but just wonder why it happens.

Jan T
J Targosz

I would suspect Convection, Jan. The Coolant is at an increased temperature around the Cylinders and Head. When the flow is stopped, it takes Convection a while to move those Hot Temps through the cooling medium (Water)to the Radiator. The Heat is sensed and the switch transfers. Not an issue as you state.
That Radiator sounds sweet!
Mike TF-8257
M Brand

Jan, we know that it's from the heat of the engine being transferred to the coolant (Mike's convection). I'll bet that the hot coolant getting into the top tank is a good demonstration of the thermo-siphon that we hear so much about. This 'after shutoff' running of electric cooling fans is not at all uncommon. It's a bit unnerving to be walking past a car and have the noisy cooling fan come on. Bud
Bud Krueger

I'm betting your electric fan sensor is one of the push-type ones that are mounted between the radiator fins. As the radiator temperature rise once the water stops moving, the fan switches on.
The electric fan will cool the water in the radiator, which will sink, drawing hot water in from the engine, and continuing the cycle until it is all cooled sufficiently to no longer trip the temperature sensor on the electric fan.
Geoffrey M Baker

The engine and coolant always gets hotter once the engine is switched off and there is no airflow around the engine itself. I read somewhere that only 25% of the heat is removed by the liquid part of the cooling system.

D Moore

Jan - Do you have any pictures of your radiator you could share with us? Sooner or later we will all need a replacement, recore, etc. Any information you would be willing to share about it I'm sure would be of interest to us all.

Thanks in advance,

John
John Mitchell

Sorry John but the radiator is fitted to the car and there isn't much to see. I had a brand new, original MG radiator that came with the box of bits. I took it to a radiator specialist in Glasgow to get the electric fan thermostat boss soldered in. They found the radiator to be useless. Despite being unused the core was totally furred up. Apparently if it had been filled with coolant it could have been OK. Being empty, dampness had combined with oxygen and had corroded the tubes. The specialist said that modern radiators are much more efficient than ones from the 1950s so I had one fitted. The cost was only £120. It is the same as the one fitted to my MG M Type. This originally had a honeycomb core but they are inefficient and very expensive. The specialist sold me a dummy honeycomb mesh for the front of the radiator shell. M Types don't have a fan and are notorious for overheating. I never had and problems with the new core. I think that anyone who is having cooling problems should consider a new radiator core.

Jan T
J Targosz

Jan - Thanks for taking the time to answer my questions. Your thread got me thinking about what options were available if and when I had to replace my radiator. The radiator specialist I've used to repair my Arnolt heater core also recommends the modern core over the old honey comb. He will do both, but when and if the time comes, I'll go with the modern more efficient route. Thanks again fo sharing.

John
John Mitchell

My Jaguar 3.8S has an electric pusher fan controlled by a thermostat and it also will cycle on and off after the car is shut down from hot. Sometime 3 times over a 15 minute period, but I like this as it ventilates the engine compartment and reduces the likelihood of fuel boiling out off the carb float bowls.
John Quilter (TD8986)

When the engine is switched off the heat from the exhaust manifold rises to the top of the engine compartment and is slow to dissipate. My 1955 TF 1500 shows a typical temperature gage reading of 175 to 180F in the hot weather in Florida prior to switching off after a run. After shutdown the reading will generally rise to 200F as the heat from the exhaust manifold radiates into the engine compartment. This is why your electric fan switches on

The original TF temperature sender fitted just before the thermostat in the 1500 has a 3/8 NPT thread. I wondered why a 3/8 BSPT plug would not fit when I took my temperature sender out to get the instrument repaired
I Massey

I installed a 10" Hayden that I bought at Pep Boys for abt. $62. I had to guess at the size when I bought it and realised when installing, that I could have gotten away with a 12" fan.

Below is a pic of my installation. Note that I have let in a VW 180° temperature sensor that I have directly wired to the fan - no switch. I intended to install a 'Manual-Off-Auto' switch, but never got around to doing it because it worked so well as is.

I should have placed the sensor in the bottom tank instead of in the header tank, but I wanted access to the switch. So I actually measure vapour temperature as the switch is rarely covered with coolant

Note too that I have mounted it as a 'puller'. This required removing the fan and the fan hub. At the time, I fitted a new, segmented fan belt. The installation is so tight, that I will have to slacken the rad to replace the fan belt, if I live that long!

But irrespective of the poorly thought-out installation, it has worked well since 2003 when I did the job.

Gord Clark
Rockburn, Qué.

Gord Clark

Jan, do you still have the old radiator (the complete unit including frame, but not the shell) and eventually looking forward to sell it? I am asking because the complete thing is missing, so I have not the opportunity to fit a new core. Or does anybody know, where to buy a new one? Thank you for reading. AlexP
Polaschek Alexander

This thread was discussed between 07/09/2015 and 19/09/2015

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