Port engine overheating - advise please

majoma

Member
Oct 10, 2008
284
San Francisco
Boat Info
2000 340, V drive
Engines
Twin 7.4
I have a problem with my port engine (2000 7.4 fresh water cooled). Up to 2000 RPM the temp stays normal but going up to 3000 RPM the temps slowly goes up to about 180 F. I had the mechanic check the hoses and change the impeller. Also I had the diver check the sea water intake which turned out to be clear from any debris. I went out today and again the temp was better but still went up at 3000 RPM. Could the heat exchanger be one of the possible causes? I normally cruise around at 2000 RPM but I would feel better if the problem gets fixed.
Thanks
 
A clogged heat exchanger could be the issue. It’s the next thing that I would check.

Can you remove the end cap and see the condition of it inside?
 
your info shows the boat as a 2000-- is it fuel injected? and if so it is normal for the operating temp of the fuel injected motors to run around 185.
 
When was the last time manifolds and risers where changed. If they are older sometimes the passages start scaling with rust and clog the passageways.
 
Thanks for your comments.
Yes, they are fuel injected engines. Great to know that the temperature could go as high as 185.
Manifolds and risers have been changed about three years ago.
Does anybody know how high the temp must be to trigger the alarm?
 
You are getting pretty close to alarming at 185. Personally I don't like seeing temps over 175 on my 8.1s. Most engines have no hotter than 170 stats. My brother in laws 7.4s have 160s in them, my 8.1s have 170s. Just some numbers for comparison.
The culprit probably is the exchangers as mentioned above. Definitely look there next. How is your raw water psi readings? Is that engine higher than the other?
 
Well, the heat exchanger turned out to be very clean. Now what? The last thing could be the riser and the mechanic recommended to try to flush it with fresh water. Any advise still very much appreciated.
 
Check your oil cooler. That is wear water goes when leaving raw water pump. What is your PSI gauge read at idle? Is it higher or lower than you other motor n by how much?
 
What you do is check the water flow volume from the raw water side. There is a spec for that. Then if that checks out, move on to the closed cooled side.
 
Well, the heat exchanger turned out to be very clean. Now what? The last thing could be the riser and the mechanic recommended to try to flush it with fresh water. Any advise still very much appreciated.
The internals of the manifolds can be checked by removing some of the plugs and poking around into the water passages. There are a few underneath too.

You can remove hoses and plugs from the risers as well.
 
Just pop a (Elbow) Riser off and check for blockage. If its clear scrap off old gasket and replace. If they are 3 seasons old its good to check them anyway. Passages should be clear and the edges of the passages should have a good edge on them.
 
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Another thing you can try is compare the temperature of the tops of Elbows to Starboard engine. You should be able to touch the tops of them. DON'T touch the sides or manifold.
 
Did you check the anti freeze in the closed system for age and temperture? If it is discolored and not a nice green color(or what ever brand you use) and needs to be at a 50/50 ratio. Old Anti freeze can cause over heating. Have a 77 240 sundancer with twin 470's and the stbd engine was running warmer than comfortable and port a little high also. So I changed both thermos,flushed the system, added new antifreeze, replaced both risers and flushed out the stbd heat exchanger. Haven't had it out to the lake since but on muffs they both run alot cooler that before. The antifreeze was old and discolored, heat exchanger had scale in it, and both risers were wore out, oh also the shutters were missing on both engines (installed new ones). Hope this helps.
 

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