Engine cooling early 80's 70 hp Mercury/Mariner

aarrjimlad · #1 October 1st, 2008, 08:51 AM

Hi my recently purchased early 80's 70hp 'Mercmar' (its a mongrel) runs well. However when started from cold it takes some time before water starts to flow through the 'tell tale' presumabley this is thermostaically controlled?

However, water droplets/vapour is ejected from two oblong slots at the top of the leg this discharge seem to be proportional to engine speed and also appears to be an exhaust type gas, is this normal?

I appreciate that the exhaust gases exit via the propellor.

Any guidance please.

Regards

Chris1956 · #2 October 1st, 2008, 10:31 AM

Most of the inline engines did not have thermostats. You might find the year by serial number at Maxrules.com, and find the exploded parts pictures at Crowleymarine.com. See if it has a thermostat.

Most motors have backpressure relief high on the midsection. These are for water and especially exhaust gases to escape, while in neutal.

There should be a grating above the AV plate, behind the prop. This and the prop are the normal water exits. if these are flowing, the water pump is pumping. Telltales get clogged easily.

aarrjimlad · #3 October 2nd, 2008, 09:41 AM

Thanks for that, not wishing to appear to be dumb, but, what's the AV plate?

Chris1956 · #4 October 2nd, 2008, 04:55 PM

The Antiventilation plate is the horizontal plate above the prop. Above it there should be some gratings, at the rear.

aarrjimlad · #5 October 3rd, 2008, 09:42 AM

Thanks for your help

willey · #6 October 4th, 2008, 05:11 PM

My 82 3cyk, Merc. takes 30 sec. to a minute before there is a solid stream, I know it sometimes seems like forever.

aarrjimlad · #7 October 20th, 2008, 12:39 PM

Had previously thought that the water pump was shrouded in an aura of mystique, a very complex component buried within the depths of the of the outboard that required expensive special skills to dismantle and replace, then again perhaps not.....
With Clymer guidance, eventually bit the bullet and dropped the lower unit, removed the pump top cover to discover that the impeller was breaking up. have ordered a replacement impeller and will refit at weekend.
Phew - I was very close to wrecking the engine, I'm really water pump aware now and will renew the impeller at regular intervals.