Engine Overheating at Higher Speed/RPM, Helpful Solution

W

WayneP

Member
Aug 20, 2019
32
Boat Info
2003 245 Weekender
Engines
383 MAG MPI
Hello All:

2002 245 Weekender with 6.2 MPI.
Been driving me crazy and tried everything. Engine would overheat at higher RPMs/speed, typically over 10 MPH. Slow down and it would cool down. Tried flushing forward and backward, checked impellor, etc. etc. . Finally noticed a junction connector in the water line coming up from port side to thermo housing? What is that thing? Well found out it was a one way anti flow back valve that was totally clogged with old impeller, sticks, small stones/hard mud etc. Seems like just enough water could get thru at low RPM but not at high. Removed valve, cleaned input side, replaced and no more overheating. Valve was not shown on a lot of manuals so not sure if all have them and if they are needed? Has anyone removed it and run OK with just a junction connection between hoses? I think it is anti flow back for the fuel cooler? Appreciate any comments.
Wayne
 
Glad you found the cause.

I'm not sure exactly what this does, but I would not remove it. It may help insure that any trapped air gets forced out of the system when the water is circulating, or make sure there is some balance between the feeds to both manifolds. Is this raw water cooled or freshwater cooled?
 
Raw water. It is yellow with a typical Merc drain on the side.
 
Pirate Lady said:
Like Bravoitis but not. Needs new name.
6.2itis ? Or Wayneitis ?
Click to expand...
Drove me fonking crazy for months. Luckily I typically zip around at LT 10 MPH but would have liked to run the engine near max for awhile clean it out.
I thought this yellow thing was just a standard M to M junction with drain port.
My name is Wayne Pleasant so how about UNPleasantitis? Now I am famous!
 
You should have followed my all summer thread last year chasing an overheating problem. Started June 5, resolved mid September. Missed the whole dam summer. Was epic. After months trying everything, we took to real mechanics who found problem in 30 mins and fixed in 2 days. ALL FKN SUMMER!! Never again. Now I found an outdrive lube leak. Did I investigate? Oh hell no. Going straight to the guys that fixed it last year next week. Boat season too short to spend chasing problems. Just pay the man. You were good you found problem.
 
I truly hear you. I had three excellent boat mechs look at it and not one found the problem. Re lube leak. On Bravo drives the thru hull fitting is easy to break plastic and the hose barb breaks off very easily. Also gimbal ring thru fitting may also be plastic barb. I had my mech replace the thru hull with the older brass fitting. Not an easy job but worth it not to worry about lube leak.
NOTE: If anyone, even the best mech, was working anywhere near this fitting, it will break. Looking at it and it will break. Thinking about it and it will break....Talking about it in this forum and it will break.....
 
Last edited:
When it was fixed last September, everything in the upper portion of the drive was replaced. Hoses, bearings, cables, sensors, everything. pretty sure it’s the prop seal. Only leaking when running.
They will find it.
 
WayneP said:
Hello All:

2002 245 Weekender with 6.2 MPI.
Been driving me crazy and tried everything. Engine would overheat at higher RPMs/speed, typically over 10 MPH. Slow down and it would cool down. Tried flushing forward and backward, checked impellor, etc. etc. . Finally noticed a junction connector in the water line coming up from port side to thermo housing? What is that thing? Well found out it was a one way anti flow back valve that was totally clogged with old impeller, sticks, small stones/hard mud etc. Seems like just enough water could get thru at low RPM but not at high. Removed valve, cleaned input side, replaced and no more overheating. Valve was not shown on a lot of manuals so not sure if all have them and if they are needed? Has anyone removed it and run OK with just a junction connection between hoses? I think it is anti flow back for the fuel cooler? Appreciate any comments.
Wayne
Click to expand...


Hello, I have 5.0 mpi having the same issue. Can you describe the location of this yellow valve you are talking about. I’ve replaced the impeller, flushed the hoses that lead into the t stat, how do you flush as you mentioned ? His just started about 3 weeks ago. Out of no where. Boat has been running great all summer. Now if I go over 3500 rpm I get over heat and pressure alarm.
 
Hello: Ok On top front of engine is the thermostat housing with hose distribution. There should be a hose coming up from the PORT side of the engine, to the thermo housing. Mine was located just after the bend to go down the front of the engine, but was an aftermarket, thus the color yellow. The anti drain back valve can also be in the same hose but lower under the side of the motor. It is after the fuel cooler. Basically you have the power steering cooler across the top back of the engine, then output to the fuel cooler , then anti drainback valve then thermo housing. You need to remove it completely to clean it out, it will not backflush. Then I ran engine for a few seconds with it removed to clean the rest of the system out. Be prepared for water to flow into the bilge so just enough running to flush a gallon or two out.
There was also a blue Mercury drainpoint on my valve. Send a pix of front of engine if you need help.
 
NOTE: I just totally removed mine and replaced with a aluminum tube the same ID as the hose. Cools even better and water does not drainback in any case on my motor.
 
WayneP said:
Hello: Ok On top front of engine is the thermostat housing with hose distribution. There should be a hose coming up from the PORT side of the engine, to the thermo housing. Mine was located just after the bend to go down the front of the engine, but was an aftermarket, thus the color yellow. The anti drain back valve can also be in the same hose but lower under the side of the motor. It is after the fuel cooler. Basically you have the power steering cooler across the top back of the engine, then output to the fuel cooler , then anti drainback valve then thermo housing. You need to remove it completely to clean it out, it will not backflush. Then I ran engine for a few seconds with it removed to clean the rest of the system out. Be prepared for water to flow into the bilge so just enough running to flush a gallon or two out.
There was also a blue Mercury drainpoint on my valve. Send a pix of front of engine if you need help.
Click to expand...
 
Thank you. If I have one I don’t believe it is yellow. Is it this ? See pic. This is located on the right hose coming out of thermostat goes down to a cooler I believe with a T connection. Hose come up to this thing just below the 2 and 3 spark plug ? I could get the front hose off. It is off in this pic. I could not get the back off. This is going into the manifold I believe ??
 

Attachments

  • 4A83F9D9-2D1B-4992-8CD0-F8B8D2CC92F0.jpeg
    4A83F9D9-2D1B-4992-8CD0-F8B8D2CC92F0.jpeg
    101.4 KB · Views: 114
Yes, that is the Mercury OEM version. My yellow one was aftermarket. inside that cup like structure is the drainback valve that can get blocked. If you cannot remove it you might try flushing each of the openings with water from a garden hose.
You might also flush the cooler while you are at it. Just a little piece of impellor and that valve can get partially blocked. since it is one way, back flushing does not seem to work. I had to take mine totally out and unjam impellor pieces with a screwdriver. Amazing the difference it made.
 
James Lee said:
Thank you. If I have one I don’t believe it is yellow. Is it this ? See pic. This is located on the right hose coming out of thermostat goes down to a cooler I believe with a T connection. Hose come up to this thing just below the 2 and 3 spark plug ? I could get the front hose off. It is off in this pic. I could not get the back off. This is going into the manifold I believe ??
Click to expand...
That's a drain back valve and has nothing to do with cooling unless it gets stuck open and prevents the full flow of water to the exhaust manifold
 
WayneP said:
Yes, that is the Mercury OEM version. My yellow one was aftermarket. inside that cup like structure is the drainback valve that can get blocked. If you cannot remove it you might try flushing each of the openings with water from a garden hose.
You might also flush the cooler while you are at it. Just a little piece of impellor and that valve can get partially blocked. since it is one way, back flushing does not seem to work. I had to take mine totally out and unjam impellor pieces with a screwdriver. Amazing the difference it made.
Click to expand...
 
Ok thanks WayneP I was able to get the front hose off but not the back one? I’ll try again I guess. How does it come out if I need to remove it. Does it screw in or is it a plug. So do I twist or pull. Lol
 
Last edited:
Could that cause my over heat issue. This thing being stuck open ?? Yesterday I pulled every hose I could get to flushed them all out. I could not reach the back steering cooler. This is the first cooler after the impeller. I was thinking a clog could be there. I couldn’t reach the damn clamps. So, I used a shop vac and tried sucking out any pieces from the impeller hose sucking back. Thought I’d get some pieces. But saw nothing.

anyway. After doing all this did take it out and it ran great. It’s running hotter the the starboard engine. But no alarms!! Star runs right around 161. Port is much higher 170-175. But no alarms. So maybe I fixed it ?
 
WayneP said:
Yes, that is the Mercury OEM version. My yellow one was aftermarket. inside that cup like structure is the drainback valve that can get blocked. If you cannot remove it you might try flushing each of the openings with water from a garden hose.
You might also flush the cooler while you are at it. Just a little piece of impellor and that valve can get partially blocked. since it is one way, back flushing does not seem to work. I had to take mine totally out and unjam impellor pieces with a screwdriver. Amazing the difference it made.
Click to expand...
 
You must log in or register to reply here.

Forum statistics

Threads
113,238
Messages
1,429,077
Members
61,119
Latest member
KenBoat
Back
Top