Water pump pressure - 1970 Merc 800

[Moody Blue]

Want to install a water pressure gauge for this motor but have no idea what pressure range gauge to buy.

The Seloc manual I have (P.O.S.) only states that there were two versions, a high pressure and a high volume types covered in the book but does not tell what years had what type. I hate this book. Should have bought Clymers, but thats another topic.

So, what pressure gauge should I be looking for? Most I've seen are 0-30PSI. Should I be looking for lower pressure, higher pressure or the 0-30PSI range?

 

[SeaKaye12]

Re: Water pump pressure - 1970 Merc 800

I think that a guage that reads 1-15 PSI is about right.

 

[emckelvy]

Re: Water pump pressure - 1970 Merc 800

I think that a guage that reads 1-15 PSI is about right.

I'll second that. An 800 with a coolant system in perfect working order will never see 15 psi so there's no point in getting a gage with higher range. The lower range gage will give more accurate readings for the pressures you'll encounter.

 

[Moody Blue]

Re: Water pump pressure - 1970 Merc 800

THanks alot for that. Found some -new-old-stock 0-15PSI units for a good price and thats what I'm going with.

Any point in having a temp gauge with the pressure gauge or is it a waste of money?

 

[emckelvy]

Re: Water pump pressure - 1970 Merc 800

A temperature gage won't save you in a case of sudden loss of water, by the time you see a rise in temp it'll be too late.

A water pressure gage will show loss of pressure almost immediately, if you happen to be looking at it at least there's a chance of shutting down the engine before it destructs.

Water pressure gage is also nice for showing a declining trend (or a sudden increase) in water pressure, this'll pick up wear in the water pump or silt/debris in the powerhead plugging water circulation.

A temp gage and water gage together might be worthwhile, you'll have a good idea of what the normal operating temp is and if it starts slowly increasing you may have time to do something about it..........ed

 

[jimmbo]

Re: Water pump pressure - 1970 Merc 800

In the 60s, 70s, and early 80s for sure, the inline engines used the low pressuse gauge, the V6s used the high pressure ( 1-30 ) type.
7 psi was about the best a new low pressure pump would put out, a bit of wear on the pump and 5 - 6 was normal.
If your engine were to lose water pressure/flow for a few moments the wter still in the block could boil and flash to steam resulting in a pressure higher than normal. I saw it happen when my friend over trimmed his engine lifting the water intake out of the water and starving the pump. Pressure gauge pinned itself and 30 or 40 seconds later a slow down followed by Silent Forward.

 

[Moody Blue]

Re: Water pump pressure - 1970 Merc 800

Great information. Thanks.

Will go with both gauges.