• Hi Guest!
    You can help ensure that British Car Forum (BCF) continues to provide a great place to engage in the British car hobby! If you find BCF a beneficial community, please consider supporting our efforts with a subscription.
    There are some perks with a member upgrade!
    **Upgrade Now**
    (PS: Subscribers don't see this gawd-aweful banner
Tips
Tips

Improving BJ8 Cooling

Share this page

[ QUOTE ]

Spinning the water pump faster will generally cause even more overheating, as the flow of the coolant through the radiator is too fast for proper heat transfer.

Jeff

[/ QUOTE ]

You know this has had me thinking for a while - and I'm convinced it cannot be true.

The rate of energy loss from the radiator is approximately proportional to the absolute temperature difference between the air and the radiator. If the water is pumped faster and the radiator thus heats up as more energy is going into it, more heat will be lost from the system not less. To maximise the loss from the radiator you want to get its temperature as close to engine temperature as possible - taking it to extremes, pumping infinately fast means that the water will be at the same temperature in all parts of the system ie engine temperature /ubbthreads/images/graemlins/confused.gif
 
Andrew,
I tend to agree with you. With one exception. Water flow restriction between engine water outlet & radiator is usually necessary. To sum up the situation, from a good reference, "The Engine Cooling System" by C.A. Mesa, published by "Technology Transfer Systems Inc."

If the coolant spends more time in the radiator to lose heat, it also spends more time in the engine to gain heat.

The "real" reasons that a restrictor at the engine outlet helps are two fold.
1- The restrictor puts higher dynamic pressure on the block & head. The local pressure in the block will be much more than the static cap pressure. Often 10 psi or more higher. This increases the local nucleatic boiling point at the hot spots, especially in the cylinder head. Once the nucleatic boiling point is exceeded at a hot spot, the steam forms a very efficient insulator between metal & coolant. (Steam pockets) High performance engines often have higher flow pumps, with the resulting higher localized water jacket pressures & velocities to minimize steam pockets.

2- The restrictor causes back pressure on the water pump inlet. (Reduces the suction) At high water pump (engine) speeds this has the benefit of reducing water pump cavitation & the resultant bubbles that are formed in the coolant. The bubbles of course reduce the coolant effeciency.

Reducing the coolant flow by slowing the pump will reduce this cavitation but at the same time reduce the dynamic pressure in the water jackets which adversely reduces the hot spot boiling temperatures. Sometimes, on modified engines which are run at much higher than design rpm, slowing the water pump to reduce inlet cavitation is the lesser of the evils.

A side issue is that high flow into a downflow radiator increases the local pressure cap unseating pressure & can cause coolant loss. This is the main reason that cross flow radiators have the filler/pressure cap on the low pressure/suction side of the radiator.
D
 
Andrew, Dave, and others. I had a long discussion with a cooling engineer, and my statement regarding speeding up the water pump was in error, although, for the reasons Dave mentioned regarding cavitation.
A bunch of us had been having overheating problems on the RACE engines, and underdriving the water pump solved the problem.
I apologize for erroneous information, and I assure you there was no malicious intent.
I'll do a bit more research next time.
Thanks,
Abashedly, /ubbthreads/images/graemlins/blush.gif
Jeff
 
[ QUOTE ]
I just had mine recored with a 4 pass.

[/ QUOTE ]
So did I & quite a few others. It helps a lot, but in 100 degree weather, heavy traffic driving still requires a very good fan, as Michael Oritt has attested to.
D
 
I am getting ready to install the new engine and recored radiator and was wondering if an overflow can would help any. This car came with a 5 bladed fiberglass fan and I was going to reuse it but after reading all this I am not so sure. Does anyone have any suggestions. Skip
 
I'm starting to sound like an old broken record.
As far as I'm concerned, the only way to go is a six staggered blade steel, engine driven flex fan. 15 inches in diameter. A fixed pitch fan with a clutch drive would be even better, but there isn't room to fit one.

A coolant recovery can, as opposed to a catch can, will assure that the system is completely full of coolant at all times with no air in the system to reduce efficiency.

A previous discussion on recovery tanks is here:
https://www.britishcarforum.com/ubbthread...mp;page=0#67134
D
 
Back
Top