Mercury Black max Compression

Firstly hello as this is my fi

Firstly hello as this is my first post and just wanted to say great site.
I have just bought my first boat and it has a Mercury Blackmax 150hp V6 to assist me in getting around in a timely manner. I decided to do a copression check just because i wanted to get to know my engine a bit better and dinner was out of the question. I am getting bang on 100psi on odd bank and 110psi on even. I know that this is a good reading as far as differences in cylinder pressures but overall is 100-110psi good for this mid to late 80's engine. Any responses gratefully recieved.

"Mark, those numbers sound ban

"Mark, those numbers sound bang on.

The compression range of these motors brand new from the factory would have been in the range of 110-135 psi with a variance of +/- 15 psi being acceptable.

There were a few different versions of the 150 Black Max over the model run including the XR2, XR4, XR6, XRI, ProMax and Super Magnum (plus probably forgot a couple).

Some were based on Merc's 2.0 litre block (121.9 cubic inch) and others on the 2.5 litre (153 cubic inch).

A couple of the models had some minor issues and overall the 2.5's tend to outlive the 2.0's by a bit simply because the larger displacement is better suited to producing 150 horses - but personally, I really liked Merc's 2.0 engines better.

If you post the serial number, can give you the exact model you have..."

Thanks for the info graham. Wi

Thanks for the info graham. Will look for the serial number next time i have the cowl off. Just out of interest i have noticed a rubber bung in the top of the head with a single wire coming out. It is between the 2 top sparkplugs and is cooroding. Any ideas what it might be.

"Those are temperature switche

"Those are temperature switches, mark. One of those is a switch to the overheat alarm/buzzer. The other is a sender for a temp gauge."