Detective needed Overheating one side only?
 

2000 7.4L MPI



Overheating on left side



Right side is cool as can be



210 on water temp gauge



Hoses on left at bottom of manifold and exhaust appeared close to melting. Could not hold hand on manifold or elbow for long at all.



Hoses entering and exiting the T-stat housing were filled with boiling hot water when I drained them to check for a blockage. Right side hoses cool.



1. Impeller- perfect and installed correctly

2. Thermostat- replaced with Merc 160 degree

3. Elbow- looks clear

4. Manifold- looks clear seals were replaced 7/6/7



My thinking on the one side hot one side cool is that the inflow of water doesn't split until the water circulator pump.



In my motor (I believe) seawater follows this flow:



-Enters thru the bravo

-Passes thru the seawater pick-up pump

-Passes thru the power steering cooler, oil and fuel coolers.

-Pases thru the T-stat

-If below 160 degrees it passes thru to exhaust manifold

-If over 160 is diverted to the circulating pump and then splits and enters the block

-Exits motor passes back thru T-stat housing exits to manifolds



I would not think it would be any of the coolers clogged, or both sides should be hot....the flow of water doesn't split until the circ pump.



Is there any secret to removing the hose from the oil cooler? It looks like removing it to check for blockage would be difficult, due to obstruction of oil cooler etceteras.



The boat is being looked at by the pros this afternoon.



I showed them the impeller, so they could skip that step.



They are going to:



-Backflush

-Check the internal exhaust flapper

-Check circulator pump



Then what?



Hoping to get back on the after for Sat or Sun....although there's a 60% chance of rain again. It has actually rained in the Austin area 33 of the last 37 days! haven't had the boat running properly since end of May!



What is the function of the bypass hose that comes off of the top of the block and re-enters the circulating pump?

What style of exhaust manifolds? If aluminum like a Gil, look for PC that has delaminated and is blocking the flow.

Suspect a blockage on that side exhaust. Water will flow in then stop, with no flow, it overheats.

Pull the hose off the t-stat housing that goes to the hot side manifold/riser. Stick the garden hose in there and see if it will run water through. Chances are it's blocked and you'll get water coming back at you :D

Manifolds are OEM original.

They have the standard light rusting on the inside, but this doesn't limit water flow.

Won't the internal exhaust flapper cause the water to backflow even if there is no blockage?

Where would I see the blockage?

I have pulled it apart at the elbow and the manifold and I cannot see any blockage?

It could be anywhere in the hose, manifold, riser...
I doubt an exhaust flapper would be water tight at garden hose pressures. If I have flappers, they're way worn out because when I run water through, it comes out no problem :D
Do you have thru-hull or thru-hub, or switchable exhaust? I'm not familiar with thru-hub or switchable, but I don't think they have flappers?
BTW, the bypass helps prevent pressure build up in the block/heads when the t-stat hasn't opened up...at least that's my understanding.

handfulz28

I have thru-hull exhaust

Thanks for the insight on the bypass

This is the diagram of my cooling system:

You must have a clogged exhaust elbow . Did you flow check it like handfulz28 suggested? I did lot read your answer. You will not see the blockage it must be flow tested. Elbows don,t last forever and the catch all the debris that goes thru the motor in addition to any scaling the motor releases.
Jim