1995 Mercury 200 EFI Overheat

mram10us

Cadet
Joined
Feb 9, 2015
Messages
25
Rebuilt my fuel pump and went to test it in a large container. Didn't see any water coming from the drain and blamed the new thermostats not being up to temp. Took it outside with the ear muffs to test and it worked fine. You see where this is going.

Got out to the lake and started her up. Ran great. I noticed the water pressure gauge read 13psi, but nothing coming from the drain. The alarm went off in the middle of the lake and steam was coming from under the engine cover. It was 45 degrees out with 50 degree water. Let it rest for a couple hours and idled it again, noticing the alarm going off even when it was cool. Tried starting it again after 3 hours of rest and it just turned over. No start. Luckily a guy towed up in to save a long trip with the trolling motor.

Got it home and tore into it. Noticed there was a wire(orange and white) coming from the starboard side head, just below the thermostat housing, that was melted to the head. Also a couple other wires that were slightly melted.

What should I expect?
 

Faztbullet

Supreme Mariner
Joined
Mar 2, 2008
Messages
15,589
Drilling the t-stats was a bad idea...water may be moving it thru it to quick to cool.
 

Faztbullet

Supreme Mariner
Joined
Mar 2, 2008
Messages
15,589
Make sure the t-stats are Merc inverted flow and not OMC as they look alike but will not interchange. Was the 13psi at idle or WOT?
 

mram10us

Cadet
Joined
Feb 9, 2015
Messages
25
I bought Sierra 18-3553 thermostats. I am going to the local mercury dealer today to get the oem. The psi was at idle, but the gauge didn't move. I plan on disconnecting it from the back of the gauge and blowing out the hose. Hope that helps.
 

Dukedog

Captain
Joined
Oct 6, 2009
Messages
3,235
if you have "melted wiring" ya might wanna do a comp check plus think about oiler delete..............
 

mram10us

Cadet
Joined
Feb 9, 2015
Messages
25
Working on the oil delete. Still need to find a how-to with pics to verify I have removed all I need to. Good idea with regards to the comp check.
 

mram10us

Cadet
Joined
Feb 9, 2015
Messages
25
I think the gauge is out to lunch. It reads 13 psi with the key off. I will mess with it and see if it will zero with the tube removed.
 

wired247

Lieutenant Commander
Joined
Oct 8, 2011
Messages
1,557
The Sierra 18-3553 thermostats are the wrong thermostats for that motor. They are OMC thermostats. They will never open on a V6 Merc despite what Sierra says or if they do they open the wrong way and they block flow. You need the quicksilver 75692Q2 kit with both thermostats and gaskets. Do not use the Sierra interchange units
 

mram10us

Cadet
Joined
Feb 9, 2015
Messages
25
Thank wired247.
I went down and got the correct ones. Works like a charm. Now I just need to drop the lower unit again because I didn't line up the freaking gear shift correctly :( Motor worked great though....
 

mram10us

Cadet
Joined
Feb 9, 2015
Messages
25
Dropped Lower Unit again. Lined up everything CORRECTLY this time. Now my water psi is fluctuating a little (+/- 3). I am going to take it down again and see what I did this time. Trial and error is the best way to learn as long as I am not cooking expensive parts :)
 

mram10us

Cadet
Joined
Feb 9, 2015
Messages
25
Took it back apart and everything seemed to be in good order. I will test it again in the morning and verify timing again while on hose.
 
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