View Full Version : AD41 Overheating at high rpm

07-30-2009, 07:48 PM
"This is a 2004 AD41 turbo 350 hrs. that was running perfect until about 3 weeks ago.

I've been experincing an overheat problem when running above 2000 rpm. I've changed the water pump impeller and thermostats, changed to new belts, added new anti freeze to adjust the level, checked and cleaned the sea water screen. There are no leaks in the system and as best I can tell no hoses are collasping under power. The heat exchanger has not been tested in any way, but with such low hours I didn't feel it is suspect.

When I back off the R's the temperture drops and I can run 1500 to 2000 all day long.

Does anyone have any other ideas or experienced a similar problem and what was the fix?

Thanks for your response in advance."

08-05-2009, 06:49 AM
"Hi Chip.
Thes if it is problem on the suction or the preasure side.
To do this, start the engine and run it on idle speed.
Then open the water filter lid, the black one on the port side on the engine, you should get ALOT of water spraying out, then you know the suction side is OK.
Start with this.

When you changed the impletter, all rubber blades was in place?"

08-05-2009, 08:06 AM
"Thanks Martin for your response.

I've performed that test earlier and the water surges up about 6 to 8 inches high and feels like excellent pressure.

I spoke with a mechanic yesterday who said the next logical place to check is the exhaust side starting with the heat exchanger to make sure it's clean and clear and then the exhaust elbow. Even though I have low hours he tells me time is also a factor.

The old impeller was craked and small pieces were missing but nothing bigger then a pea. At first I thought this was the problem with it being in such poor condition, but as soon as I got to the high rpm's the temperture starting rising again.

Any thoughts?
Thanks again."

08-05-2009, 08:34 AM
"The best tool to use in this case is an IR heat gun. You may get them rather 'cheap', depending on where you live.
The key point to measure is raw water out from exchanger to raiser.
If that stays 'stable' but the engine internal temp rises, you have most likely an internal circulation problem, or even a dirty heat exchanger.
If the temp rises abruptly at the same time as engine temp, you have a raw water problem. It might be water in, but might as well be a restriction in the exhaust bend not letting the water out."

08-05-2009, 10:48 AM
I'm on the case to check those out, but you're right with the idea to use the IR gun as a quick way to check that, thanks.


08-05-2009, 06:25 PM

Morten is correct, but you can also put your hand on the elbow, if it is very hot you have a raw water problem, if it is cold you have a internal circulation probem, or heat excanger problem.
One other thing, have you checked your temp sensor on the engine?, the sensor might be the problem showing you wrong information on the dash."

08-06-2009, 12:23 AM

I thought Mort's idea of the IR gun was a good one in that I could check a multitude of areas at once to see what kind readings I get.

I have a heater on board and I tried using that to help cool down the engine faster and it started out being hot, but cooled quickly could that be a hint as to which side is the problem? I haven't traced the two hoses back to the engine yet, but that just came to mind.

The gauages could be a problem but both the temp gauge and the alarm sound and I think they are indepentant of one another.

If it's not the exchanger or elbow I don't where I'm going next. All I know is I'm losing valuable time on doing my favorite past time.


08-06-2009, 10:44 PM
"Hi Chip,

I had same problem with my own KAD43 The raw water intake hose from leg to transom shield was plugged with mussel and barnacle shell. This may not be a problem if you don't live on the coast. That particular hose is worth checking out anyway as it can collapse and restrict water flow."

08-07-2009, 08:00 AM
"Thanks Perrie,

I Live along the Deleware River in New Jersey, but the boat was previously in the bay along the Atlantic Ocean. Did the problem come on all of a sudden or was something that happen over time? The boat ran perfectly and then suddenly one day it overheated and hasn't stop since


10-04-2009, 11:12 AM
I had the same problem on a kad43 it turned out to be twofold. the hose from the leg to the shield had a minute hole in it and the leg had about 6 tiny stones stuck in the intake. as the leg was running in airated water on the plane it just wasn't sucking enough water through. At 3900 revs it's on the absolute limit of leg/engine performance and the tinyest thing can tip the balance.