Cooling system blockage - Best approach?

[Clucas]

Having a major cooling system headache with my late model raw-water cooled A4... Engine starts and runs fine but no cooling water is coming out the exhaust. Had water coming out the exhaust when pulling from a bucket on the hard, though the observed flow seemed a bit light. Did an acid flush last fall prior to winterizing her and installed a new impeller this spring (the 'old' impeller was intact and a year old - cheap insurance).

I verified impeller shaft is turning and verified prime by pulling from a bucket leading directly to waterpump intake.

Now for the ugly part... when I start the engine and advance the throttle, I can feel suction on the end of the hose in the bucket for a second or two, then the suction stops since the water evidently has no place to go. When I reduce the rpms, I can feel some cool water coming back into the bucket. When I STOP the engine, warm/hot water drains back through the system into the bucket. Moving my bucket to the t-fitting I use to winterize (upstream of a Groco strainer) and had hot water backing up into the strainer and into the bucket.

So... blockage. Somewhere. Since the water coming back is hot, it is making it into the the water jacket at least, correct? (Note: No thermostat, just a bypass valve). Suggested approach?

I'm thinking:
a) Verify waterpump flow by running a hose from waterpump output to a bucket and running the engine for about 15-20 seconds. Don't expect any issues here since water is coming back hot when I run the engine until about 150 degrees.
b) Try the same thing running a hose from the output of the thermostat housing. Poor flow == issue is upstream. Good flow == issue is downstream.

Assuming waterpump flow is good, test flow from bypass hose? (possible identifying a issue within water jacket?). I figure the water isn't getting too far since it draining back through the waterpump when I stop the engine.

Thoughts? What am I missing?

[Dave Neptune]

First check the clearance on the impeller. It isd not uncommon to replace the impeller and find that it is actually to narrow for the cavity. They will not make much pressure or suction and liquid can easily run through a non moving pump~not good.

Try pulling the crossover hose from the top of the block to the manifold on late models. Also check the exit fitting on the manifold as it is a very common place to get plugged up after knocking a lot of crap loose.

Make sure the pump impeller fits tight on the "sides" first them start checking lines starting at the pump. Also confirm that the through hull is open by removing the inlet hose on the pump too. May have just sucked something in after splashing.

Dave Neptune

[Sam]

Easy mistake to make [don't ask me how I know] is the impellor is mounted on the shaft "backwards". Depending on the pump and the brand [I use oberdofer] the impellor has some very small protrusions on one side that must be mounted toward pump. Otherwise seal against back plate is compromised.

[Clucas]

First check the clearance on the impeller. It isd not uncommon to replace the impeller and find that it is actually to narrow for the cavity. They will not make much pressure or suction and liquid can easily run through a non moving pump~not good.

Worth a shot trying one of my tried-and-true spares to see if it makes a difference.

Try pulling the crossover hose from the top of the block to the manifold on late models. Also check the exit fitting on the manifold as it is a very common place to get plugged up after knocking a lot of crap loose.

Yeah -- want to check the flow here. I figure if it's bad, I can open up the water jacket side plate and clean that out (did so a few years back). If the flow is good at the crossover, next step will be the manifold exit.

Make sure the pump impeller fits tight on the "sides" first them start checking lines starting at the pump. Also confirm that the through hull is open by removing the inlet hose on the pump too. May have just sucked something in after splashing.

Dave Neptune

Thanks, Dave.

[Clucas]

Problem solved

Problem solved! Clog at the water entry to the exhaust hot section. Put my favorite marine specialty tool to work - coat hanger wire. Fixed!

[CajunSpike]

This is the 3rd recent case where the flow to the exhaust system, from the manifold was impeded in some way.

[Clucas]

This is the 3rd recent case where the flow to the exhaust system, from the manifold was impeded in some way.

A first for me -- as noted above, I change the impeller every year as cheap insurance and did an acid flush last fall before winterizing. The blockage could fit on my fingertip (I tried to pull it out rather than push it through), but then used some coat hanger wire to chase the water entry in the hot section.

[ndutton]

Good find but it leads to a few other questions:

• Where did the clog come from? Was it rust detritus from the engine or a concentration of silt/organisms from the water in your area? Maybe a combination of both?
• Acid flushes can be effective up to a point. They can also launch particles (rusticles?) into the flow that can get lodged downstream blocking flow. For the first time through I've always felt an acid flush should be in conjunction with a cooling system examination to be sure there are no blockages the flush either left behind or may have caused. Following my first acid flush (the engine had been RWC for 30 years at the time) I removed the water jacket side plate to inspect the side plate Tee and internal diverter, also physically mucked/chiseled out the encrustation surrounding the cylinders. All hoses were replaced (they were due anyway) and the elbows too. For me this was in preparation for FWC but the follow-up cleaning applies to RWC as well.
• Have you pulled the new thermostat to be certain it doesn't have any debris affecting its performance?
• Speaking of which, now that you've found one major system clog, how is the system doing? Much improved? What is the current operating temp under load?
• Do you have any raw water filtration?

Regardless of the improvement you may have achieved, in my opinion the job isn't done until the cooling system has been dismantled and thoroughly inspected and cleaned out. If you have a potable water heater installed that becomes part of the cooling system so it needs checking too. An obstruction there is just as bad as anywhere else.

[Clucas]

Good find but it leads to a few other questions:

• Where did the clog come from? Was it rust detritus from the engine or a concentration of silt/organisms from the water in your area? Maybe a combination of both?
• Acid flushes can be effective up to a point. They can also launch particles (rusticles?) into the flow that can get lodged downstream blocking flow. For the first time through I've always felt an acid flush should be in conjunction with a cooling system examination to be sure there are no blockages the flush either left behind or may have caused. Following my first acid flush (the engine had been RWC for 30 years at the time) I removed the water jacket side plate to inspect the side plate Tee and internal diverter, also physically mucked/chiseled out the encrustation surrounding the cylinders. All hoses were replaced (they were due anyway) and the elbows too. For me this was in preparation for FWC but the follow-up cleaning applies to RWC as well.
• Have you pulled the new thermostat to be certain it doesn't have any debris affecting its performance?
• Speaking of which, now that you've found one major system clog, how is the system doing? Much improved? What is the current operating temp under load?
• Do you have any raw water filtration?

Regardless of the improvement you may have achieved, in my opinion the job isn't done until the cooling system has been dismantled and thoroughly inspected and cleaned out. If you have a potable water heater installed that becomes part of the cooling system so it needs checking too. An obstruction there is just as bad as anywhere else.

All good questions, Neil. I believe the clog came from a 'rusticle', as you called it. I am moored in a clean harbor in Long Island Sound in about 18' of water. I removed the water jacket side plate several years ago to clean out and inspect the T and diverter. While there, I also used a magnet to get as many rust particles as I could (plus a very thorough fresh water flush afterwards). I don't have a thermostat and use a bypass shutoff valve to regulate temperature -- if anything, I run on the cool side (more because I don't usually run the engine that long), but operating range is usually 140-ish.

As far as raw water filtration, the raw water intake goes to a Groco strainer which has been effective - no exterior strainer however. Two (?) years ago, I had the joy of removing a used condom that had gotten sucked into the raw water intake -- never made it as far as the strainer. Nasty.

Racing tonight but running the engine awhile beforehand. Afterwards, I plan on pulling in a gallon of vinegar and letting it sit for 12-24 hours.

This may be the year I convert to FWC...

[ndutton]

Tom Thatcher, 'Thatch' (one of the big dawgs on the forum) preaches the advantages of FWC. It is the only way to arrest the cancer of RWC. When Tom posts, folks would do well to pay close attention.

About clean raw water, it also has a wide range of life in it and skeletal remains can form deposits in the water jacket that turn into the consistency of concrete.

[thatch]

I actually paid Neil to say that. Seriously though, there seems to be an alarming number of manifold and block rust-outs lately. With the newest of the Universal blocks reaching almost 40 years old, it's not surprising that this is happening. I realize that a FWC conversion is pricey, but consider the alternative.
Tom