Mercruiser 5.0 MPI overheating

[russvanatter]

Have 2006 5.0 MPI Bravo one that consistently runs about 205 degrees f. Idle temperature hangs out just slightly above 175. Once underway water temp slowly rises to around halfway on gauge between 175 and 250 degrees f. Returning to idle doesn’t seem to bring the temperature down much. Running WOT for more than a couple minutes sounds over temperature alarm on engine. Sea water pump has new impeller and seals and is in good condition.

 

[QBhoy]

Did it overheat before the water pump was replaced ? If so, you may have a blockage caused by a melted exhaust flapper. Is one riser hotter than the other ?

 

[alldodge]

Have 2006 5.0 MPI Bravo one that consistently runs about 205 degrees f. Idle temperature hangs out just slightly above 175. Once underway water temp slowly rises to around halfway on gauge between 175 and 250 degrees f. Returning to idle doesn’t seem to bring the temperature down much. Running WOT for more than a couple minutes sounds over temperature alarm on engine. Sea water pump has new impeller and seals and is in good condition.

When was the last time the raw water ump impeller was replaced and inspected?

What is your motor serial number?

Has any codes been noted?

 

[russvanatter]

Sea water pump impeller replaced late last season. I pulled the pump and inspected it and it look new. Just starting through troubleshooting matrix in manual. Will get back to you on serial number.

 

[russvanatter]

Haven’t checked the risers yet, but will do.

 

[alldodge]

Place a clear tubing between thermostat housing and seawater pump. Your checking for air bubbles.

If your in salt water it may be bravoits

 

[russvanatter]

Serial number is 0W35727. Not running in salt water. Found kinked hose from starboard exhaust manifold to cool fuel manifold. Replaced it, however no change. Removed and cleaned thermostat and housing. Lots of crud in there, but no change. Water discharge from transom housing is noticeably warmer on starboard side than port side.

 

[QBhoy]

Serial number is 0W35727. Not running in salt water. Found kinked hose from starboard exhaust manifold to cool fuel manifold. Replaced it, however no change. Removed and cleaned thermostat and housing. Lots of crud in there, but no change. Water discharge from transom housing is noticeably warmer on starboard side than port side.

Really good reason to check that flapper in exhaust.

 

[alldodge]

Serial number is missing a digit but close enough
Do you have the multi port or easy drain system?

Assuming open cool?

 

[russvanatter]

Open cool. Air actuated drain system with single point. Starboard flapper is gone, however port side is still intact.

 

[russvanatter]

On the engine mounted raw water pump, should the inlet hose be on top and supply line on lower nipple?

 

[russvanatter]

Exhaust risers are cool to touch, manifolds are warm to hot. Seems like an engine core water circulation problem. I remove drive belt and spun circulating pump and can hear it sloshing water around.

 

[alldodge]

These easy drain systems are great when new, but over time they have some real issues. IMO wish they never would have developed, but I digress

The primes is restrictors and check balls allows everything to fill with water, and those restrictions cause water to flow in the correct directions (water flows to the area of LEAST restrictions).

The issue is when things get more restricted or less then water flows other directions.

This is what I think is going on.
Item 20 is a Tee which is used to create a slight restriction so water will flow easier toward the bottom of the manifolds. It does allow air to escape and fill with water so elbows are full.

When thermostat opens this allows more water out thru the mans then up thru the elbows.

The check balls item 10 in lower pic is there to seal off any water going up thru when motor is running. This keeps cooling in the block and the mans and stops cooler water from just escaping out thru mans. If the check balls get to the point they do not seal shut then more water passes by them and not going to the block

The check balls are there for easy winterization





Suggest get something to clamp off the hoses (item 3) going up to each manifold so water can not pass. Then take for a run and see if temps change

 

[russvanatter]

The water line that you mentioned above (item #3) was completely collapsed with two kinks. I replaced this hose and it seems to have flow, however I think I will remove the check valve fitting from the engine and clean and inspect. I have new thermostat arriving today, however I believe a full engine flush is necessary. Can you explain what "Bravoits" is and how do I recognize this condition and treat it?

 

[russvanatter]

Since the flapper from starboard exhaust is missing, what I a good way to retrieve the missing pieces ?

 

[alldodge]

Bravoits is when the inlet water hose swells and collects crud so flow is reduced. It normally doesn't happen in fresh water, mostly in salt. Its the connection at the transom



The retrieve the flapper, get a grabber
https://www.homedepot.com/p/GrabEas...7Mwm-MWnJ-Nl66SCUb4aAiJzEALw_wcB&gclsrc=aw.ds

 

[juhasev]

These easy drain systems are great when new, but over time they have some real issues. IMO wish they never would have developed, but I digress

The primes is restrictors and check balls allows everything to fill with water, and those restrictions cause water to flow in the correct directions (water flows to the area of LEAST restrictions).

The issue is when things get more restricted or less then water flows other directions.

This is what I think is going on.
Item 20 is a Tee which is used to create a slight restriction so water will flow easier toward the bottom of the manifolds. It does allow air to escape and fill with water so elbows are full.

When thermostat opens this allows more water out thru the mans then up thru the elbows.

The check balls item 10 in lower pic is there to seal off any water going up thru when motor is running. This keeps cooling in the block and the mans and stops cooler water from just escaping out thru mans. If the check balls get to the point they do not seal shut then more water passes by them and not going to the block

The check balls are there for easy winterization


View attachment 271974

View attachment 282700
Suggest get something to clamp off the hoses (item 3) going up to each manifold so water can not pass. Then take for a run and see if temps change

This is fantastic reply! And the only one advising to check these check valves! My other riser runs 30 degrees cooler than the other one (and also the other engine), I could almost guarantee that the check valve is malfunctioning! Thanks again!