WhySoSearious?
Seaman
- Joined
- Apr 25, 2012
- Messages
- 64
Why So Searious? (WSS) reminder:
if you have fresh water cooled Mercruiser 496 engines, don't forget to backflush your raw water passages.
I heard the heat exchangers get clogged often so I did mine and tons of debris came out. It was much easier than I thought. The raw water flows from the drive intakes, to the water pump/impeller, to the fuel cooler, to the power steering cooler, to the oil cooler, and to the heat exchanger (i've seen 2 diagrams with different orders, depending on year). the oil cooler and the heat exchanger are made of tubes inside (like honeycomb) which can easily get blocked/restricted. If you're experiencing high water pressure or increased engine temps, this is definitely for you.
Here's what I did.
Prep
1. ordered replacement heat exchanger gasket and oring for the end caps.
2. made an adapter to attach a garden hose to a 1.5in OD tube/pipe. I added a high flow valve for better control.
3. ordered a rifle cleaning kit - .17 caliber (I think the flexible Otis ones are good. you have to get the small caliber set for air rifles). I also ordered nylon and brass brushes because I didn't know which i needed.
4. bring power drill and extension cord (or extra batteries for your cordless).
5. flashlight
6. air pump - inflatable toys type
First I backflushed the oil cooler. I think this is where the first honeycomb mesh would be, so I assumed this had the most junk. I didn't want to push the junk back all the way to the water pump, so i removed the hose behind the oil cooler and flushed it from the heat exchanger hose.
1. remove hose behind oil cooler (intake side)
2. remove heat exchanger raw water intake hose.
3. attach hose adapter to #2 hose.
4. turned on the water and watch the junk come out of the oil cooler.
I used a snake cam to look inside the oil cooler. It was clean after the flush.
Then I flushed the rest of the system.
1. remove hose from behind the water pump (NOT the red hoses that come from the drive intakes. those are under the waterline!).
2. reattach hose behind oil cooler
3. turn on water to flush for a few minutes.
Then I cleaned the heat exchanger. If your heat exchanger has scale, you may need to do an acid bath. My tubes were clear, just some debris which I cleaned out with the rifle cleaning kit.
1. remove end caps of heat exchanger
2. sprayed water through the tubes to get most of the debris out
3. insert rifle cleaning brush through the tubes. Mine was not bad so i only used the flexible tube to push debris through (if any). I did not have to use a brush. If i did have to use a brush, i was prepared to attach one end of the tube to a power drill and slowly brush the inside with the drill in reverse.
4. I used the air pump and blew all the water out of the tubes. Then I was able to use a flashlight to see through the tubes to make sure they're all clear.
5. Insert new gasket and oring back onto the end caps and reassemble.
Replace all hoses and clamps and double check for leaks.
let me know if anyone has questions or need more details.
It was very satisfying for me to backflush the cooling system because it was easy and I saw debris come out. I'm actually looking forward to doing it again next season!
if you have fresh water cooled Mercruiser 496 engines, don't forget to backflush your raw water passages.
I heard the heat exchangers get clogged often so I did mine and tons of debris came out. It was much easier than I thought. The raw water flows from the drive intakes, to the water pump/impeller, to the fuel cooler, to the power steering cooler, to the oil cooler, and to the heat exchanger (i've seen 2 diagrams with different orders, depending on year). the oil cooler and the heat exchanger are made of tubes inside (like honeycomb) which can easily get blocked/restricted. If you're experiencing high water pressure or increased engine temps, this is definitely for you.
Here's what I did.
Prep
1. ordered replacement heat exchanger gasket and oring for the end caps.
2. made an adapter to attach a garden hose to a 1.5in OD tube/pipe. I added a high flow valve for better control.
3. ordered a rifle cleaning kit - .17 caliber (I think the flexible Otis ones are good. you have to get the small caliber set for air rifles). I also ordered nylon and brass brushes because I didn't know which i needed.
4. bring power drill and extension cord (or extra batteries for your cordless).
5. flashlight
6. air pump - inflatable toys type
First I backflushed the oil cooler. I think this is where the first honeycomb mesh would be, so I assumed this had the most junk. I didn't want to push the junk back all the way to the water pump, so i removed the hose behind the oil cooler and flushed it from the heat exchanger hose.
1. remove hose behind oil cooler (intake side)
2. remove heat exchanger raw water intake hose.
3. attach hose adapter to #2 hose.
4. turned on the water and watch the junk come out of the oil cooler.
I used a snake cam to look inside the oil cooler. It was clean after the flush.
Then I flushed the rest of the system.
1. remove hose from behind the water pump (NOT the red hoses that come from the drive intakes. those are under the waterline!).
2. reattach hose behind oil cooler
3. turn on water to flush for a few minutes.
Then I cleaned the heat exchanger. If your heat exchanger has scale, you may need to do an acid bath. My tubes were clear, just some debris which I cleaned out with the rifle cleaning kit.
1. remove end caps of heat exchanger
2. sprayed water through the tubes to get most of the debris out
3. insert rifle cleaning brush through the tubes. Mine was not bad so i only used the flexible tube to push debris through (if any). I did not have to use a brush. If i did have to use a brush, i was prepared to attach one end of the tube to a power drill and slowly brush the inside with the drill in reverse.
4. I used the air pump and blew all the water out of the tubes. Then I was able to use a flashlight to see through the tubes to make sure they're all clear.
5. Insert new gasket and oring back onto the end caps and reassemble.
Replace all hoses and clamps and double check for leaks.
let me know if anyone has questions or need more details.
It was very satisfying for me to backflush the cooling system because it was easy and I saw debris come out. I'm actually looking forward to doing it again next season!
