Mercruiser 4.5 overheating

[Drnick]

2016 sea ray with 4.5 250 hp V-6 with 40 hrs, went into safe
mode with overheat alarm,just made it to dock, have
mercruiser platinum warranty,service mgr. suspects risers and exhaust manifolds, took risers off and cats out, all looked ok, looked into exhaust manifolds and noticed port side carboned up uniformaly (normal) and starboard I noticed small spots where carbon didn’t adhere? Boat has been meticulously maintained. Before I remove the exhaust manifolds myself ( because warranty isn’t worth the paper it is written on! any advice. Thx

 

[Bondo]

Ayuh,..... Welcome Aboard,..... The impeller in the raw water pump is always the 1st place to look, in an overheat situation,......

 

[Drnick]

Bondo, no, my water temperature was normal when I got alarm,when I opened engine hatch I noticed a haze,and the smell of burning paint I also noticed paint discoloring on starboard header,I’m assuming that after I removed and inspected risers and cat elements,and all appeared normal, I suspect it’s the actual exhaust manifold on starboard
40 hrs!! Unbelievable

 

[Lou C]

Check water supply to the hot manifold.

 

[Drnick]

I removed both risers and manifolds, pressure tested all,
everything flowed ok,poppet valves on both were free of any
corrosion,and were working ok, exhaust system in its entirety
looked excellent (only 40 hrs!) I have no idea why starboard
side overheated, and neither does Merc tech! The only
thing I can think of is the rear poppet valve that has 4 hoses
connected to it? From what I can see, it’s none of the
exhaust components!!

 

[alldodge]

No matter what it has reduced water flow to the starboard manifold.

The only thing I can think of is the rear poppet valve that has 4 hoses connected to it?

Only thing I can see with 4 hoses is with the open cooled system and its for draining during winterization. Where is the rear poppet valve you mentioned? My thought is the check valve on the SB side got stuck and now its free.

This is 4.3 but should be similar

 

[Drnick]

All dodge, 4.3 looks a lot less complex then the 4.5, each manifold has a tee fitting on bottom which incorporates a poppet valve and 3 hoses! Bottom hose on tee is a “drain”
and the other two hoses go to other areas, those 2 poppet valves are ok no rust, no corrosion, the other poppet valve is much larger, has 5 hoses connected to it!, one is supply, the other four go to risers and bottom of manifolds ( that tee fitting)
ill try to post pic of flow diagram, it’s somewhat complex, and I truly believe it’s that poppet valve with the 5 hoses attached.

 

[Bt Doctur]

If thats the "quick-crack" drain system ,remove it completely and use manual drain plugs

 

[Drnick]

How do u post pics on this forum, it’s telling me on pic is to large?

 

[Drnick]

Better pic?!

 

[alldodge]

Thanks for the pic,
I think that system is a problem waiting to happen. Appears to work off resistance flow, so if one area starts clogging the other side gets more flow, same goes if one side has less resistance then the other side gets more.

The mans get flow from 2 places, and excess goes to elbow and out. Item P can make or break the system from my thinking

The single point drain (will crack) does look better then the old style

 

[Drnick]

I’m gonna check “p” if I can reach it! It’s buried I. The back of the motor! 5 hoses are connected to it, I’m surprised that no one else has this problem, but then again, it’s a newer motor
and had no history.

 

[alldodge]

ok sounds like a good plan

 

[Ken Stephens]

All most the same problem here I Have a 2017 Mercruser 4.5 250 horse Bravo 3. Showing low block pressure alarm occasionally after a long run. Temp never gets above 149. It starts out with good block pressure at 18 to 20 as the day goes it may drop to 7 or 5 psi. at the same rpm. Always shows 2 to 3 psi at idle. Sometimes it alarms and goes into guradian mode. No showing any code checked by dealer. Is my boat haunted. Driving me crazy. Oh and it only has 50 hours on engine.

Thanks Guys

 

[jdinner]

Hi all, I am new to the forum. Had the same issues. Here is the history.
A friend bought boat with twin 4.5L 250hp mercs in it. He was getting Port engine/starboard exhaust overheating alarms on this first run. Previous owner had TWO sea pumps replaced under warranty on the same port engine. First week of using it the oil pan filled with water and was hydro-locked. I inspected (mechanic for over 45 years) and found starboard bank cylinders full of water. Cranked without plugs to clear the water, replaced oil and filter and started the engine. Runs perfect. Went for 20 minute cruise, idled for 5 minutes, then shut it down for gas. It was hydro-locked again after filling with gas.
I removed the starboard cylinder head and found the headgasket in perfect shape. I then made up a water pressure tester for the starboard exhaust manifold, it was leaking internally. I replaced with a used manifold. Reassembled, tested all good.
Ten minutes at WOT on the lake the same alarm comes back on and engine power is reduced. Starboard exhaust is over temperature. I replaced the sensor with the used one. Same problem.
I replaced the sea pump impeller - old one looked in perfect condition.
I then started measuring the exhaust temps with a laser temp gun. Both engines show the starboard manifolds about 40*F higher than the port manifolds. My suspicion of a major design flaw built into the rear water distribution Tee (5 hoses going to it) seem to be correct. ('P' in the above pictures)
I have worked on older Lamborghinis with the same sort of tee that always overheated so I wanted to test my theory.
On the port exhaust riser coolant hose feeding the riser between Q and O in the diagram, I attached a pair of needle nose locking pliers to the hose to restrict the water flow slightly. I tested at WOT multiple times and tested the manifold temperatures until I dialled in the locking pliers so both manifolds were the same temperature. PROBLEM SOLVED.
Now for a permanent fix I am going to make an electric control system that will regulate the water flow to the port manifold riser/elbow. This way the manifolds can stay at the same temperature. This design flaw should be addressed by Mercruiser.

 

[GA_Boater]

@jdinner

All you're doing is adding more complication to an already over-complicated cooling system.

And you managed to cause the thread to be closed because it has been inactive far longer than our customary 90 days. Please read our rules.