8.1L cooling water restriction

I have a 2007 vintage 8.1L that has zebra mussles somewhere in the cooling water flow. I had trouble winterizing the engine. It would not draw coolant out of a bucket like normal even with a brand new impeller. I got 6 gal of coolant into it eventually. I catch the exhaust in a waste basket. When I poured the coolant out of the waste basket I found zebra mussles and mussele parts.
Looking at the engine parts maniual it looks like I may have a restriction in the engine oil cooler , the transmission oil cooler, or main heat exchanger.

My question is are all these circuits in series or are there parallel paths for water to flow? If in series then I feel like I got all the water out and coolant into the system. If parallel then maybe there is still water in one of the coolers?

Any opions appreciated.

"series" is more accurate...

Agreed, I would start with the intake strainer on the hull and work your way back. If you don’t have inline strainers, that might be worth adding. In my case, I’ve thought about removing them because I go years between cleaning the baskets.

Bob

The strainers were clear. I have found that there are two hoses on the raw water pump outlet. One goes down each side of the motor under the heads and come up to the large heat exchanger on the top rear of the motor. In each of these hoses is an in-line oil cooler. One for the motor and one for the transmission. What I don't know is what these in like coolers look like inside. A bundle of small diameter tubes? If so, then I would think any impeller blades that come off would end up there and not inside the big heat exchanger. Is that what others have experienced?
I'm trying to figure out if the zebra mussels are likely obstructing these oil coolers or the big heat exchanger. The oil coolers look like a big effort to remove. I would first remove the hose end at the heat exchanger and try to reverse flush them rather than remove them. Any advice on that appreciated!
I have found a product called Barnacle Buster that will reduce the mussels shell to mush. I'm going to use that if I can get it into the entire raw water-cooling circuit and let is sit for a while I believe the system will flush itself out. My idea to first back flush the oil coolers is to get them clear enough to suck up
Barnacle buster from a bucket....like I do when winterizing. Any insights on this appreciate.

Thanks

i think the engine cooler sits in the suction hose feeding the raw water pump...the gear cooler is in the pressure side.

the gear coolers are as you described...if you can get the appropriate hoses, then backflushing them is a viable approach...we do it all the time on the old big block U coolers....

i would concentrate on the oil coolers as their water passages are much smaller that the HX...

Wow. I never caught that the engine oil cooler was in the suction side! Looking at the engine parts diagram it is open on one end and goes to the pump on the other end. The pump is shown with only two ports. So, one is obviously the input and one the output. The transmission cooler is clearly in the output side and goes to the heat exchanger. Thanks for point that out!

John

We have a pair of older 8.1s as well. we also had a raw water problem. several actually. We did find one of the issues to be worn out hoses on the suction side of the raw water pump had failed in that the wire coil inside had basically dissolved and allowed the hoses to collapse.

Learn something new each day! We were again having a creep up in engine temps. Everything seemed normal but... we found that we had installed the tstats upside down. It's just the opposite as we had all done in our cars over the years. After a bit of discussion and carefully viewing the HX assembly in the parts drawing, we discovered that the spring side needs to facing upwards and the pointy side down. duh.