1986 Mercury Black Max 175 overheating

**Dayton12** · 05-31-2018, 10:22 AM

Sorry, was 35 psi ( gauge pegged) at WTO, at idle or just off 5-10 psi, and 2000 rpm about 20 psi

**Bruce2** · 05-31-2018, 10:25 AM

Originally Posted by bullet123

I'm not sure if it would create enough pressure to open poppet. I just reread this entire post. In post #1 you said you had 35 psi @3000 rpms and in post#13 you had 20 psi @2000-3000 rpms. Two totally different situations. Ideally you want 20-30 at WOT and 5-8 at idle. If you have a good psi gauge and your poppet is working properly, you should see pressure drop at around 2000 rpms when poppet opens (if my memory serves me right). Have you pulled poppet and made sure all parts are there?

This is why i asked him if he pulled the poppet valve out and put the housing back on the block and then try flushing to see if there was water coming out where it should be.

**Dayton12** · 05-31-2018, 11:05 AM

Just to confirm, and as stated in long test list, when poppet is out and flushed either back or through the water inlet lots water out of the poppet hole. With poppet valve in place, cover on, and full garden hose water pressure through the water inlet pipe, the poppet valve did not open.

**bullet123** · 05-31-2018, 12:30 PM

Pressure that high points to restriction as stated earlier. Since you have flushed everything and you think poppet is working proper. Take it for a test drive. If you still have high pressure and overheat problem, then you need to find the restriction. Could be blockage in plates under powerhead or in the block itself. You said poppet and waterpump looked newer. Maybe previous owner replaced those parts in hopes it would fix problem and decided to throw in the towel.

**nitro_rat** · 05-31-2018, 12:41 PM

Originally Posted by bullet123

You said poppet and waterpump looked newer. Maybe previous owner replaced those parts in hopes it would fix problem and decided to throw in the towel.

I’m thinking it’s not something simple.

**rock** · 05-31-2018, 01:30 PM

If you look at my first post you will see that is more or less my thinking also. Adapters plug and when they do you get ridiculous pressure and very hot very quick at wot. I suggested as a last resort since everything else is easy and quick to do. Fixing plate is fairly easy just a bit time consuming and will require a couple gaskets. Hopefully it don't get hot now so removal of the powerhead not necessary.

Rock

**Dayton12** · 05-31-2018, 02:06 PM

Ok, spoke to bullet (thanks) thinks W pump might be incorrect. After looking and more research, my serial number off the welsh plug shows it is XR6 (i have to add a zero in front of B otherwise search shows nothing), seems same as black max but merc cruiser parts diagram shows my water pump without the seal that slides down the driveshaft and sits on the top of the waterpump.

**bullet123** · 05-31-2018, 02:13 PM

#36 in the diagram for your motor

Click image for larger version.

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**rock** · 05-31-2018, 03:42 PM

If you have one or are in a position to get one I would love to see a picture of this powerhead.

Rock

**Tripps** · 05-31-2018, 06:49 PM

I had one that had massive wip but ran real Hot ,it was a pwrhd. I found ,the block. Head surface was not flat between cylinders and the compression was going into water jacket !!! That had me going for a few days,but not as bad as the flywheel that caused massive misfire after I changed every ING piece, then swapped wheel easy fix