Cooling system diagram help.

[Dave Bilyk]

I searched a couple of times, here and on the net, but never found a diagram. The attached diagram shows is how I think the standard cooling circuit is set up. I left out the expansion tank, what I am more wanting to establish is the circuit through the block / heads and how the bypass works. Is this right? any comments?

regards
Dave

 

[Jac Mac]

MAIN COOLING CIRCUIT:From Radiator lower to large pump intake then into both banks of block, along block into heads at rear, out front of heads into intake manifold, then bypass back into pump until t/stat opens to allow flow thru to top of radiator.

HEADER TANK: feed by small line(-3 or -4 ) immediately above t/stat on manifold side to high up on header tank ( but below cap ). Take 5/8" or 3/4" hose from bottom of header tank to lower fitting on pump ( you may have to use a TEE if also using this point as heater return.)

RECOVERY/EXPANSION TANK: This is fed from fitting at filler neck of radiator cap on header tank to the expansion tank- this should be mounted higher than header tank if possible to enable easy recovery of excess coolant after shutdown--- I see some cars on the forum with this tank mounted down around trans etc, IMHO this just makes it that much harder for the coolant to be recovered.

OPTIONS: If motor is fitted nose down then it may be necessary to fit a small (-3) bleed line from each side at rear of intake manifold to header tank, also from top tank of radiator to header tank.

 

[Dave Bilyk]

Thanks Jac,
the diagram seems consistent with that.
Reason for asking, - despite alloy radiator, correctly operating fans, and a high flow thermostat, and rear head bleed, indicated temperature still climbed to over 100degC in traffic. The fans cut in at 80degC, but fail to stop, the inexorable climb in temp. I know the cooling capacity is there as I get 65degC with a drilled thermostat.
So, one possibility is that the bypass flows slightly too much, (sized for front engine/rad), with smaller alloy rad, and with long flowpath in GT40, the resistance to rad is greater and so at low rpm, all bypass and very little flow to rad.
Now what I want to do is experiment by introducing a valve or orifice in the bypass, and see if that does the trick.

best
Dave

 

[Ian Anderson]

Dave
Where did you find traffic in Scotland?
Now believe it or not opening the valve to allow water to flow through the heater matrix in the cabin will not assist the cooling - in fact the opposite as it again causes an easy route for the water and reduces the flow through the rad.

Something found a number of years ago when people were fitting the Rover V8 into MGB's and the instruction was not to open the valve at all on a warm - hot day thereby forcing the water through the radiator core.

So along these lines I would think a restrictor in the bypass would assist with the cooling

Ian

 

[Mike Drew]

Thanks Jac,
the diagram seems consistent with that.
Reason for asking, - despite alloy radiator, correctly operating fans, and a high flow thermostat, and rear head bleed, indicated temperature still climbed to over 100degC in traffic.

At the risk of asking the obvious, are you sure your 'correctly' operating fans are in fact doing so?

The reason I ask is that it's quite possible to induce overheating problems like the ones you put forth by having the cooling fans spinning *backwards*. Sure, they operate, i.e. they turn on and off at the proper time. But a fan spinning backwards will lead to these kinds of problems straightaway.

It sounds silly, but quite a few Pantera guys have been caught out like this. Some of the most popular aftermarket fans we use have a black and red wire; the black wire is for 12v and the red wire is for ground. Yet the assumption among most people is that red is always hot, which leads them to rig them up backwards.

If your car isn't overheating when on the move, then that validates the rest of your cooling system (water pump, radiator etc.), and the problem seems to be caused by a lack of airflow through the radiator at low speed. So take a hard look at those fans. There should be a jet of hot air coming from the bonnet vents when they're on, and they should be able to suck a piece of paper against the front of the radiator.

Let us know how you get on.

Cheers!

 

[Mark Clapp]

Dave, sorry if I missed it, but I don't see that you have a bleed line from the top of your radiator back to the header tank (fill tank, highest place in the system). It may be that you're building steam air there after a bit and getting reduced flow. I just saw that Jac Mac suggested the same thing.

 

[Brian Durbridge]

Hi Dave
this might be of some use

Brian

 

[Dave Bilyk]

Ian,
yes I know, sometimes I have to pretend that there's lots of traffic and drive slowly just so I dont feel lonely:laugh3::tongue2:.
The overheating occured in traffic jams on the way down south and in France around Le Mans.
You're right, path of least resistance is the way I'm thinking too.

Mike,
thanks, yes I checked fan rotation and they seem to blast well, there's not much back pressure either as the chassis is not panelled at the sides, so air exits freely into the wheel area.
Mark,
you are right, I don't have a radiator bleed line, and that maybe should be on my to do list, but I have religiously bled the radiator, and never had any sign of steam or air. The temperature builds up very slowly once the thermostat opens at 80deg, and on tickover so I don't believe that it could be steam or air. The fact that temperature increases so slowly suggests that it wont take much of a change to fix this, that is why I think that a small change in the balance between bypass and rad circuit might do the trick.
Brian,
nice diagram, thanks. I have to get working on this too, as I am shamed by my plastic header tank held on with cable ties at present:embarassed:.
best
Dave

 

[kiwi ka]

Jacmac Thanks for the drawing offer,
I seemed to remember this article so searched under `cooling sytem diagram` and it appears to answer what my question was to you. Basicly it is easy to get into the system in those two points to install a by pass hose which I thought would have been around the 1/2 to 5/8 dia. Whilst open, I planed to drill a few holes in that thermo, say 5 or 6 at 6mm....good or bad? Out of curiosity, what is the relative difference in oil and water itemperature in the same block as a ageneral rule.

MAIN COOLING CIRCUIT:From Radiator lower to large pump intake then into both banks of block, along block into heads at rear, out front of heads into intake manifold, then bypass back into pump until t/stat opens to allow flow thru to top of radiator.

HEADER TANK: feed by small line(-3 or -4 ) immediately above t/stat on manifold side to high up on header tank ( but below cap ). Take 5/8" or 3/4" hose from bottom of header tank to lower fitting on pump ( you may have to use a TEE if also using this point as heater return.)

RECOVERY/EXPANSION TANK: This is fed from fitting at filler neck of radiator cap on header tank to the expansion tank- this should be mounted higher than header tank if possible to enable easy recovery of excess coolant after shutdown--- I see some cars on the forum with this tank mounted down around trans etc, IMHO this just makes it that much harder for the coolant to be recovered.

OPTIONS: If motor is fitted nose down then it may be necessary to fit a small (-3) bleed line from each side at rear of intake manifold to header tank, also from top tank of radiator to header tank.

 

[Jac Mac]

Knew I done it somewhere,
Russell, by drilling holes in the T/Stat you virtually eliminate the need for a bypass, but the motor will take longer to warm up & in some cases may never reach full operating temp with the result that the t/stat will then not open properly & allow full flow- thereby virtually making the t/stat into a restrictor--Not Ideal!!!

By positioning the by-pass take off point as close to the t/stat bulb as possible it makes the t/stat function as designed.