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Penta AQAD40 heat exchanger

jascat

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My engine is overheating at anything above 2,500rpm. I replaced both thermostats, which were faulty. No change, so I tried without thermostats. No change again. I used car radiator flush to try & clean out the fresh water system. The rubber impeller in the seawater system is ok. The seawater system is clear & pumping plenty water. When the engine is very hot, the seawater pipes are cold.
I think the heat exchanger requires cleaning. There is an end plate facing the front of the engine, which I removed & some crusty deposits came out. It is not possible to remove the element out the front, as there is no room. At the other end is a large rubber bellows with hose clips. Is it possible to get the element out that way? I don't think it has been removed since the boat was new (1989)
Or is there some stronger chemical solution I can soak the exchanger in, without trying to remove it?
I am wary of damaging the element if I try to remove it. It is probably corroded in place.
Any advice welcome.
 
I have two TAMD40s and one of them was having the same problem you are having. The problem ending up being in the salt water systems. There are 3 coolers on the TAMDs, I'm not sure about yours. The oil and heat exchanger were just about completely plugged. I tried removing these coolers in the boat but found it too confined and had both engines removed. I completely cleaned the cooling systems in both engines and had the coolers boiled at a local rad shop. There are some products that claim to remove this built up, salt away is one. But I think after there is a large amount of build up it might not be affective, more for maintenance.
If you have the space on your boat the cooler/s and housing could be removed and cleaned. Caution when removing the cooler from the housing, the cooler is fairly delicate. I used a hammer and a piece of wood. Tap the wood against the housing while holding the cooler.
Good luck
 
Trying to avoid having to remove the engine.
I need to know if the element can be removed from the rubber bellows end. If not, I suppose I could cut a hole in the front engine fibreglass bulkhead big enough to feed it through from the front of the engine.
The best option, if possible, would be some strong chemical agent I could add to the water, that would not destroy hoses etc, but clean the element.
 
That element is not going to be removable after all these years, as its most likely fused to the housing due to corrosion.

If your seawater pipes are cold, when engine is overheating, there is obviously problem on seawater side. Seawater is used to cool the engine down, so it has to be warm (because its taking heat away from the motor). Anything under 2500rpm is not loading the motor enough to overheat, and as soon as you put load on it temperature comes up.

Most likely you have restriction in the seawater system. Check in this order:

intake grate (for blockage)
raw water pump impeller (for damage or spun hub)
oil cooler (for blockage on the front side)
aftercooler (for blocked tubes, can be seen through drain plug opening w/out removing)
heat exchanger (for blocked tubes)
exhaust elbow (rust blocking passages inside jacket)

You can use dishwashing detergent (no suds) in the freshwater system to clean out the deposits. Cascade. Then flush with tap water while engine is running until it comes out clean. Then add coolant to approx 50/50

To clean H/E element, you can remove front and rear cover, and use ~4mm rod to ream out the tubes until you can see daylight from the opposite side on all of them.
 
Thanks for all the advice.
The heat exchanger was remarkably clean. I removed the front plate, started up the engine & a good supply of water came through the supply side of the element. I ran a 4mm stiff plastic tube through all the return element holes, which seemed clear, then attached a hosepipe to the seawater outlet pipe drain cock. This back flushed the return side of the element & I got an equally good water flow.
I put some dishwasher powder in the freshwater system & took the boat out for a run, then flushed it out. After all this, I can now get 3000rpm & temp stays at 90c. A noticable improvement.
I will do the dishwasher treatment again, as the first treatment seemed to remove a lot of crud.
 
Great news. Dont even add coolant until you are done flushing with powder, it will run fine with tap water alone.

Next check for raw water flow at Exhaust Elbow, its easy to remove and inspect. Usually gets clogged with rust, use screwdriver and ream it out and shake out the blockage. If the raw water can't get out fast enough, it cant carry away the engine heat properly. Good exit flow at elbow is essential.

Another important thing is a correct position of the rubber end cap on the H/E. It has a seam in it, that has to seat into the divider, if its distorted or crooked it will allow water to bypass the H/E. Self-explanatory when you remove it, you will understand.

Put thermostats back in, they are there for a reason. Never a good idea to run without them, this is not a Chevrolet :)

Seems like you are well on your way to sorting it out :)
 
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In addition to all the good advices given, you may also check for parts of the zink anodes that possibly have partly blocked the cooling tubes of the oil cooler. You have already been into the front end of the heat exchanger where the same might take place, and would easily have seen some if they were there.

Finally, the same problem that you have was on my engines solved by checking inside the raw water intake in front of the stern drives. By checking thoroughly, I discovered lots of small shells inside. They were removed by a steel wire or similar. Remove rubber hose from drive and clean drive water channel thoroughly and flush with high pressure fresh water. Do also check the the rubber hose between stern drive, and might also be an option if the other advices given fail to give a succesful result. Remember to check and evt. clean raw filter. Good luck!
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Tried some more dishwater powder in the freshwater system, with not much more improvement. Although the cooling is adequate for the speeds I normally use, I looked for something else to clean the freshwater side of the system.
It is difficult to find suitable chemicals here in Cyprus.
I came across "trac descaler" on the internet & its make up is mainly Phosphoric acid. You can use it in the cooling system without removing anything.
After some searching, I found a product here called HG hagesan blue. Its make up seemed much the same as the Trac product.
My freshwater system holds five gallons. I drained down just enough to empty the heat exchanger unit & added two litres of hagesan blue & topped up with water. I left the exchanger soaking in this mixture for a couple of hours, then went out in the boat for another couple of hours. Left the engine to cool, then drained down the system. Lots of rust & muck came out. Flushed out the system & added some soda ash (from my pool supplies) to counter any acid left in the system. Flushed out again & filled with fresh water.
The temperature now is below 90c at full power (3,400rpm) which is good enough for me.
I will refit the thermostats tomorrow, along with some rust inhibitor.
Thanks for all the tips guys.
 
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