Tech Help on a 1980 Mercury 200HP 2.4
 

Due to a water pump failure, my engine overheated and hoping to make it back to port, I continue to navigate until the rubber grommet on the temperature sender melted and started to smoke. Shut it off and it did not start again. Compression tested all cylinders and got about 65 psi, way below the 120 psi I should be getting, but then again, all of them at 65 psi, very interesting. By the way, I do the compression test with all plug out. Inspected the pistons and found no scoring on the sleeves. Replaced both cylinder head gaskets and still the same compression. :cry: Any suggestions? Thanks!

Man that sucks!!!

Sounds like you are in for a trip over to Ferms place for a rebuild.

Get a new compression tester also make sure it's screwed in all the way and your battery is charged.

Both batteries and the tester are good - however I noticed that with plugs installed, the motor drags when cranking. Dismantled the starter and brushes are good. Checked all piston with the cylinder head off and they are working. What a bummer...:fight:

How does it turn over by hand with the plugs out? Any signs of aluminum on the sleeves when you pulled the heads? The uniform reading across the board makes me think the same as BS does, bad guage. IIRC them there 2.4's are chrome bore engines(or NICASIL for the XR4). Pretty tough to tear em up, but if you do it's normally cheaper to find a good used powerhead to swap out. You either have to re-plate them(NOT CHEAP), or have sleeves put in for around $200 a hole.

THEFERM, It turns over very easy by hand without the plugs and I found no sign of aluminum when I pulled the heads.The sleeves are smooth and shiny with no scoring whatsoever. Could it be the piston rings going bad due to overheating?

The rings could have collapsed, but that is not very likely with keystone beveled rings. If your want to find out if it's the rings, put a tablespoon of oil in the cylinder then do a compression test and see if the numbers go way up. If they do then it could be your rings.

With all electrical components out, I was removing the manifold and I got to thinking... Since the cylinders and the exhaust are interconnected, is it possible that the overheating burned parts of the two gaskets that go in between the cover and divider plate creating a leak and thus the reason for my low compression on all cylinders? What do you think...maybe, possible or just wishful thinking? :head:

I doubt that is it. But you can get a better look at the pistons by removing the exhaust plate and divider. Rotate the crank by hand and look at the sides of the pistons thru the exhaust ports. Its just odd that they are all down the same amount

Sorry Builder. That's definitely not the problem.