Mercruiser 5.0 EFI Temperature hot

I have twin 5.0 L EFI Bravo II engines. The starboard engine gets up to 170-175 degrees within 5 minutes at idle at the dock. The port engines takes much longer to warm up and never gets above 160 during cruise. I replaced both impellers which seemed to be in good shape. I replaced the thermostat housing on the starboard engine. I also swapped the temperature sending units and got the same result. The thermostat on this engine is a 160 degree. Does this temp seem okay? It seems high to me. I also when changing the impellers blew through the hose that has the oil coolers and no contaminants came out. Any info would be a great help.

Re: Mercruiser 5.0 EFI Temperature hot

anssec66 said:

I have twin 5.0 L EFI Bravo II engines. The starboard engine gets up to 170-175 degrees within 5 minutes at idle at the dock. The port engines takes much longer to warm up and never gets above 160 during cruise. I replaced both impellers which seemed to be in good shape. I replaced the thermostat housing on the starboard engine. I also swapped the temperature sending units and got the same result. The thermostat on this engine is a 160 degree. Does this temp seem okay? It seems high to me. I also when changing the impellers blew through the hose that has the oil coolers and no contaminants came out. Any info would be a great help.

Click to expand...

Ayuh,.... Welcome Aboard,... Is this a Saltwater boat,..??

While water has to be able to get into the system, 'n yer changing the impellers is a Good thing,...
Water also has to be able to get Out...

Have ya pulled the risers lately to see if they're gettin' plugged up,..??

Re: Mercruiser 5.0 EFI Temperature hot

It is a fresh water boat. Its a year 2000. I have not pulled the risers off yet to see if they are plugged. I just bought an infared temperature gun to see the temps of the different parts of the engine.

Re: Mercruiser 5.0 EFI Temperature hot

have you checked the thermostats themselves. simply looking at the numbers on the bottom doesnt mean anything. use a thermometer and a pot of water. put them in the water, put the pot on the stove, and raise the temp until they start opening. use the thermometer to read the real temp.

the ability of a massed produced pellet of wax to be perfect to exactly open at 160 would be a miracle.

Re: Mercruiser 5.0 EFI Temperature hot

I replaced the thermostat and it did exactly the same thing. I did forget this one piece of evidence. When I pulled the temperature sender out and swapped them, the water felt like bath water (100 F). Right before I took them out, the engine was ran and the temperature showed 170 F. Shouldn't that water be still around 170 degrees after I shut the engine down and took 2 to 3 minutes to remove the sending unit?

Re: Mercruiser 5.0 EFI Temperature hot

I have just had the pleassure of replacing a number of parts in search of a Overheating engine issue.

I have a 2005 searay 240 w merc 5.0 MPI Bravo 3LEG.

I spoke with a Australian mechanic who i could not get the Boat too who suggested that it is common that salt build up around the hose and Grommits which goes through the transom and constricts water flow. This was also suggested on a coulple of forums - and in posts here.

The Mechanic i am forced to use due to the boats location told me there is no way it was the Salt Build up or constriction in the transome.
"i have been working on Mercruiser engines for 50 years!!!" so who am i to argue.

Anyway having replaced thermostat, checked manifolds, replaced water pump, bypassed the fuel cooler which was (not needed in Victoria Australia) leaking,
starter and alternator for other reasons. We / i have paid for the final cause and discovery of the problem which is infact the Transom grommit.

The Engine had to come out to work on the back of the transom, which in searay's is incredibly difficult to access!


The hose which goes through transome is NARROW! The Grommit fittings further constricts waterflow.
This is a point where high waterflow is required.



Examining this fitting and the size of hoses through out the engine, it is very tight considering the importance of HIGH flow here !!!
Mercruiser should be looking at redesign! I know this is unlikely, considering the investment Mercruiser have sunk into the Bravo 3 leg.


Has anyone relaced the thru transome hose on a searay sundeck without pulling the engine out ?

I would Buy another Searay but wouldnt do it without knowledge of the state of this fitting and waterflow.


Bring on Summer DOWN UNDER !

Hope this helps!

Regards Andrew

Re: Mercruiser 5.0 EFI Temperature hot

So, today I spent the whole day working on this thing.
1. I checked the newly install impeller to make sure it was still together and installed properly.
2. Checked all oil coolers and made sure they were clean with no blockages.
3. Replaced leaking water circulating pump
4. Tested 160 degree thermostat. It opens at 160 and is fully open at 180
5. Replaced water temp gauge.
6. Swapped temp sending units from starboard to port engine
7. Ran engine. Idle within 5 minutes the temp was 175. When I got on plane it was stabilized at 190. The risers remain cool. While thermostat housing shows 155 with the infra red temp gun.
8. Removed thermostat. Ran engine at dock and the engine never came up to temp.It was showing 95 to 100 degrees for the 15 minutes i ran it at idle.
Not too sure what to do next. The boat is 10 years old, and has never been in salt water.

Re: Mercruiser 5.0 EFI Temperature hot

trust the heat gun, not your gauge. you engine is running at 155 based on the heat gun. your gauge is off by 35 degrees.

you heat gun is manufactured out of higher quality parts than the cheap air-core gauge used as a temperature gauge.

and yes, without the thermostat the engine will NEVER come up to temperature.