MD7A cooling water flow rate

[penfold]

As far as I can make out the pump on your engine is a 3/8" Johnson type but I have not been able to get any data on the 3/8" Johnson howver the Jabsco website give a flow of 10 l/min at 1500 rpm at 3 m head for a 3/8 pump and as the pump on your engine is (I THINK) driven off the camshaft and that runs at half engine speed then you be pushing out 10 l/ min at full speed and say 7 l/min at crusing speed (ish)

Added. I have just read your original post and noted that you are getting 2.5 l at 1200 engine rpm. This would give a water pump speed of 600 rpn so that would equate to about 3.3 l/min (assuming the graph was linear) at that engine speed.

Is your engine overheating when under load?

Those figures for 3m head are not much use in a zero head installation; that said I was basing my expectations on the HP rating and the assumption of indirect cooling. The posts from those with direct experience of the MD7 are probably the most relevant.

OP, don't write off your thermostat housing and exhaust manifold just yet; depending on how much meat is left it may be possible to build up the the mating surfaces using filler; epoxy will stick best, but car body filler may work depending on the geometry of the repair. The most long lasting repair would be to use one of the metal loaded fillers but they are expensive; how long do you think the rest of the engine will last for?

 

[Lodesman77]

Yes indeed. Ours is at the age where putting a lot of money into it might not be too clever. Having said that, if I could get manifold, thermostat housing and exhaust elbow second hand then the top end is in pretty good shape. Might then be worth having the head off to clear all the cooling passages and get the valve seats seen to as well.

Still hoping I'll find some specific fault to cause such a sudden change in behaviour, but I've ruled out all the simple ones that I can think of.

Exactly where I've just been with mine - second hand parts are scarce to say the least, and not usually in great condition. But some time and effort cleaning up what you have will pay dividends. Would suggest you pull the manifold first, which should give you a good idea of the condition things are in. I can sort some photos if it would help. And I can confirm that plastic metal can work...

 

[gandy]

I am afraid your figures are meaningless as you do not say if you have indirect cooling or if the engine is unloaded. these both make a big difference.

It's direct cooled, I had forgotten that some MD7As have been installed with indirect cooling. It appears to increase slightly once the engine's hot, maybe 3 litres/minute or slightly less.

 

[Bilgediver]

It's direct cooled, I had forgotten that some MD7As have been installed with indirect cooling. It appears to increase slightly once the engine's hot, maybe 3 litres/minute or slightly less.

Would be interesting to get a comparison from another engine. Is the 3 LPM at
tickover or 2500 RPM. That is about what I probably get at 800 RPM on my MD2B.

 

[gandy]

Would be interesting to get a comparison from another engine. Is the 3 LPM at tickover or 2500 RPM. That is about what I probably get at 800 RPM on my MD2B.

All my measurements were at 1200 rpm. At tickover there are such long pauses between gobs of water that I'd have to measure it over a much longer period, that's why I settled on a faster speed.

 

[DerrickHigton]

MD7A

Just a thought, but does all the cooling water go into the exhaust? On my boat there is always just a small trickle out of the exhaust, but some of the water is diverted through the prop-shaft Cutless bearing to help with its lubrication.

One other thing, my water pump stopped self-priming after wear on the pump cover. Replacing the cover cured the problem and increased the flow a bit.

I converted my MD7 to indirect cooling some twenty years ago after internal corrosion led to a head gasket failure.