overheating

[allan horsfall]

Gentlemen,

In the absence of being able to do anything of substance recently, Ive been concentrating on the teething problems of the car (not that there have been that many).
However, although at a steady 55-60 all remains stable, once I get to 70-80 she overheats quite rapidly.
Im running a tuned 3.5 with a MGB V8 radiator.I dont think there are any restrictions in the system and Im sure the instruments and thermostats are all OK, so I think its the fan.
Im running a blower fan on the front of the rad? Im wondering if a sucker on the rear of the rad would be a lot more efficient?
Its surely got to be better to pull the air through, than have an obstruction on the front of the rad blowing it?
Is there any difference in the design of blowers and suckers other than the wiring and rotation direction?
Im also wondering about changing to a Kenlow fan.

Any views would be appreciated

Regards
Allan

[Karl]

When a car overheats when travelling fast this has nothing to do with a fan. You can travel without the fan working, no problem. Fans are only for slow traffic and when the car is not moving. In this situation for me a sucker is better. When your car gets hot during driving, there must be something blocking, restricting the waterflow. Can be the thermostat not opening enough, part of the cooler blocked or the return hose collapsing. Thermastat you can take out and check the opening in hot water, volume of cooler (capacity) can be checked by draining and measuring whilst refilling and the bottom hose you can watch when the car is stationary with the engine at high revs. Trapped air can alsohave an influence on the water circuit flow.
Karl

[Paul Blore]

What Karl said.

[clive]

I think the bottom hose is probably the most suspect. Is it a single length of rubber hose? If so try using a length of tubing with short rubber hoses at each end, this will prevent the hose from collapsing when there is a high demand from the engine.

[allan horsfall]

Hi Karl/Paul,

My thinking is, does a fan on the front of the rad impede the airflow through the rad when its not working?
Whereas a sucker on the rear of the rad wouldnt impede the airflow?.

Allan

[allan horsfall]

Hi Clive,

Thats what I've got.

Allan

[Karl]

Allan, my son has a MGB GTV8 with a slightly uprated engine. It has a sligthly bigger oil cooler in front of the rad and two different sized sucker fans. When he had a problem with the otter switch he did a lot of driving without the fans, only connecting them when he came into city traffic. In this car some of the cooling area is behind body parts, so not all of the area is exposed to the wind and also the air does not escape the engine compartment easily. The temp gauge only went higher when he would hit slow traffic or traffic lights. If it is a pusher or a sucker does not make much difference, as both obstruct airflow.
Karl

[Paul Blore]

I suspect you would get a better airflow through the radiator with a non-running fan behind rather than in front due to the more linear airstream, whereas a fan in front of the radiator will cause turbulence. However, I have absolutely no proof and it's no more than a gut feeling.

I also think that fans in front of radiators look pretty ugly, unless they're period fans with aluminium blades as fitted to 427 S/C Cobras, but they're next to useless at providing cooling.

Paul

[289 Baz]

Just something else to think about, at that speed it could be down to the engine running lean, have you had the car set up on a rolling road?
At that speed your carb should be just transitioning onto the main system and the idle circuit (remember that it not only controls the idle circuit but also the low speed running circuit) is just phasing out.

Barry

[allan horsfall]

Hi Barry,

Not ignoring you, just a bit tied up this week. Thats an ineresting thought, I have had it rolling road tuned, (I had to get emissions down for IVA) , but Im now wondering how well it was done. I think Im going to look at the fan position issue first and then the carb set up if its still playing up. The temperature increase is not radical, its just a slow and steady rise until its to hot at the higher speeds. So I feel its something quite small that wiould make all the difference?

Regards
Allan