Engine Runs hot coming off plane

[Espos4]

Engine runs at 158-161 degrees on plane all the time. Cruising at 3,000-3,600 rpm.
Water pressure has always been 1 psi at idle 9-12 psi cruising. Does not overheat while cruising although max water pressure this year is around 9 psi.

Since I bought it in 2016, When I Come off plane, temps would to rise to 166-170 and quickly cool back to 158
THIS year, coming off plane to 1,000 rpm (2.5 psi water pressure) engine temp has risen to 180 - 188, and on 2 occasions hit 195 and the alarm sounds.

2007 240 Sundeck 350 MAG B3 raw water cooled 575 hours
Salt water boat its whole life
Water inlet inspected every year, no bravoitis.
Fresh water flush kit installed and used after every trip
160 thermostat new his year
raw water pump impeller new last season 75 hours on it since installed
Raw water pump housing has 300 hours on it.
Circulating pump replaced spring 2021 and now has 150 hours on it.
Manifolds and risers installed Spring 2018 at 300 hours.

I’m leaning towards raw water pump housing or circulating pump impeller issues.


any thoughts?

 

[Strecker25]

I’d pull the elbows and get a good look at the risers and manifolds first. That’s a lot of time of them and maybe they’re clogged enough to slow water flow at particular RPMs

 

[techmitch]

Does your cooling system have that odd plastic check valve or what ever they call it that I have seen in other running hot threads?

 

[Espos4]

Does your cooling system have that odd plastic check valve or what ever they call it that I have seen in other running hot threads?

No, not the plastic check valves. But I do have the brass valves that screw into the center hole underneath the exhaust manifold. I did consider that they could be clogged and affecting water flow.

 

[Espos4]

I’d pull the elbows and get a good look at the risers and manifolds first. That’s a lot of time of them and maybe they’re clogged enough to slow water flow at particular RPMs

I did consider that too.
But I thought that clogged exhaust would give me higher raw water pressure. I haven’t seen an increase in raw water pressure.

Gaskets alone are over $200, if I am going to remove 6 year old elbows, I’d probably just replace the manifolds and elbows.

 

[jmcdboater]

I’d pull the elbows and get a good look at the risers and manifolds first. That’s a lot of time of them and maybe they’re clogged enough to slow water flow at particular RPMs

I like @Strecker25’s thoughts, and would definitely check the impellers, they’re prone to malfunction…..

 

[Espos4]

I like @Strecker25’s thoughts, and would definitely check the impellers, they’re prone to malfunction…..

I did consider that my circulation pump impeller may be deteriorating. Is it possible for the raw water pump to supply enough water flow to keep it cool at 3,000 rpm even with a bad circulation pump impeller?

 

[jmcdboater]

I don’t have enough experience to answer that, but someone in this club does, keep asking.
I will say I’ve had overheating issues twice, one was an old manifold that was leaking, and the other was an IMPELLER!

 

[Golfman25]

I did consider that too.
But I thought that clogged exhaust would give me higher raw water pressure. I haven’t seen an increase in raw water pressure.

Gaskets alone are over $200, if I am going to remove 6 year old elbows, I’d probably just replace the manifolds and elbows.

6 years, saltwater -- might be time, no?

 

[mrsrobinson]

I did consider that my circulation pump impeller may be deteriorating. Is it possible for the raw water pump to supply enough water flow to keep it cool at 3,000 rpm even with a bad circulation pump impeller?

Good ole Gary/FourSuns got after me about this many years ago with my 330DA that had the same symptoms. I don't recall the "science" around it, but your impeller has to do more of the work at lower speeds/when the boat is not moving thru the water. Check your impeller, actually, if you have to check it just replace it. That fixed my same symptom issue.

 

[Espos4]

Good ole Gary/FourSuns got after me about this many years ago with my 330DA that had the same symptoms. I don't recall the "science" around it, but your impeller has to do more of the work at lower speeds/when the boat is not moving thru the water. Check your impeller, actually, if you have to check it just replace it. That fixed my same symptom issue.

Just to clarify, are you referring to the raw water pump impeller or the circulating pump ?

 

[Scott215]

Does the boat sit on salt water the whole season

 

[Espos4]

Does the boat sit on salt water the whole season

Yes. Wet slipped 6 months a year since new.

 

[Scott215]

I can always put the scan tool on it and make sure your numbers are The same as what the scan tool says

 

[Espos4]

I can always put the scan tool on it and make sure your numbers are The same as what the scan tool says

Not sure what that means?

 

[Scott215]

Sorry you can always put a scan tool on it and make sure your gauges and everything is reading correctly Merc mechanic would have it

 

[Espos4]

Sorry you can always put a scan tool on it and make sure your gauges and everything is reading correctly Merc mechanic would have it

I believe the data is correct because it has Smartcraft. The temperature and water pressure readings are digital displays of info from the computer.

 

[Scott215]

Look into the raw water pump is my guess

 

[ZZ13]

Just a data point in case you want to consider it, not necessarily related to your issue. I am in 24/7 salt environment. I have several friends with Mercruisers that pushed their manifold/riser replacements into the 6 year mark. Most around here just preventatively replace at the 5 year mark. There have been several sudden hydrolocks among that 6 year group. Sample size isn’t large since most boats here are diesel inboard or trailered outboard.

 

[Scott215]

I flush my boat motor and outdrive after every use with salt away