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Water flow fundamentals

S

stevebar

New member
"Let me start by saying that I

"Let me start by saying that I probably am in over my head on trying to fix a number of problems. I've been in an ongoing struggle with a 7.4 V8 Thunderbolt. It's been winning and has been sitting on the lift since last summer. The most recent challenge has been overheating. I changed the impeller last weekend and the old one was disintegrated. I know I should backflush the system but am not sure how to do that. Maybe from the thermostat? I've attached what I think is the correct diagram for my engine cooling system.

Actually that may be secondary. When the new impeller didn't do the trick I went back to basics and removed the seawater intake hose from the seawater pump to make sure there was water coming in. When I tried to flush by putting a hose on the garden hose flush attachment on the outdrive there was zero water from the hose. I'm thinking that's not right. True? Could sitting on the lift have caused some corrosion of the inlets? My plans was to check that idea out this weekend but like I said I'm a real rookie with this and maybe there is something more obviously wrong. I'd appreciate some guidance. Knowing what you're doing is a wonderful thing.. I guess!

Thanks...

Steve

170770.jpg
Cooling diagram
 
"Steve;
Not sure I am getting

"Steve;
Not sure I am getting your drift completely on where you have flow and where you don't.
If you disconnect the pump inlet hose at the pump, you should be able to freely flush the line back to the pickups on the drive. If not, its plugged somewhere and you need to start dissassembling.

Next, if you disconnect the water inlet hose at the T'stat housing and at the pump outlet fitting, you should be able to freely flush it back to the pump. This line is where you are likely to find impeller debris lodged in either the PS cooler or the lube oil cooler.

If these lines both flush clean and free, then reconnect everything except the T'stat inlet hose. With water connected at the intakes, briefly run the engine and flow water from this hose into a bucket. You should get about 7 GPM at 1000 RPM idle, so it should fill the bucket in less than 1/2 minute. If not, something is wrong. Don't run the engine except briefly in this manner.

Rod"
 
"Rod,

You answered what I w

"Rod,

You answered what I was trying to ask...Where to backflush and that there should be water freely flowing from the disconnected inlet hose. I guess its pretty basic.. unless you're not sure what you're doing!

Thanks for your help,

Steve"
 
One step forward one $tep back

One step forward one $tep back. Flushing the system seemed to do the trick. There was a lot of crud that came out and now the seawater pump has good output. However...after only a few minutes of running the engine a bunch of what looked like white smoke started coming from the port side of the engine. !@#$%^ When things cooled down I took a closer look. When I felt under the exhaust manifold which seemed to be the location of the "smoke" I ended up with a hand full of rust. Lots of rust

I'm thinking that the manifold needs to be replaced and that the smoke was actually steam. Does that make sense? This is becoming a true boat story..

Thanks for your thoughts...
 
"Sounds like you are in the ma

"Sounds like you are in the market for new manifolds and risers alright.
Are you running in salt water?
If so, they only last a few years.
Consider going to stainless to get more life out of them. Expensive though.

Rod"
 
Yikes!! I'm on the Gulf c

Yikes!! I'm on the Gulf coast of Florida and the engine is in a 1990 Searay. I think the manifolds are the originals so it sounds like they may have been on borrowed time for a while. Thanks for your help...

Steve
 
Some get as little as 3-5 year

Some get as little as 3-5 years in salt water with cast iron manifolds. So 18 years is not bad at all.

Rod
 
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