FWC overheating even when raw water exiting

[Dave Corning]

Hi all!
Taking over my old man's sailboat and A4 engine maintenance is new to me. I've been spending hours reviewing and reading forum posts, this web site is the bomb.
We have a late model A4 with FWC. Years ago the raw water strainer was removed and never replaced. Engine hasn't seen a lot of use over the last 5 years or so, maybe 20 hours combined.
Engine began overheating during a sailing trip up the eastern shore (NS, Canada). Steam from the engine compartment as the coolant boiled over (we don't have a overflow/recovery bottle, it just dumps to bilge). A healthy amount of raw water still ejecting with the exhaust but we still double checked the sea water intake valve, raw water impeller, and hosing up to heat exchanger. Due to lack of strainer we then found and removed a healthy clump of seaweed salad in the raw water access port on the heat exchanger, but this didn't resolve the issue.
I believe the issue lies somewhere with the cooling system. The coolant ran dry but I believe this was due to boiling over but could a coolant leak be possible?

Here are the things that come to mind but I need help to figure out if I'm on point, missing anything, and what order of operations make sense:
- Blockage in the seawater tubes of the heat exchanger? We poked around with a narrow screwdriver but didn't find much.
- Thermostat blockage or failure?
- Coolant pump blockage or failure? (Is there some way to visualize whether coolant is flowing through the lines?)
- Manifold blockage? (Am I even correct that the manifold is the rectangular box right next to the block where coolant flows from the tstat housing to the manifold then to the heat exchanger?)
- could a downstream blockage in the exhaust cause the overheating conditions as described? Again, getting healthy amount of sea water exiting out the back

As far as order of operations, I'm thinking to first remove and asses tstat and clamp bypass line to gauge whether full coolant flow through engine solves problem.
Then, open up coolant pump to see if any blockage in impeller.
Then, check manifold output for blockage.
Then, somehow blow out heat exchanger?

What am I missing...
Any and all advice welcome.

Regards,
Dave C.

[Surcouf]

I will let the tough guys answer.
But regarding how to check if coolant is flowing through the lines, the easiest way is to disconnect the flex hoses staring at pump discharge, then making your way further down the system, start the engine, dump the coolant in a bucket so that you can check flow. If needed you may have to feed the pumps with a line + funnel. That will allow you to identify any plugged exchanger or line / broken impeller etc...

[Administrator]

Are any of the vets among us familiar with the concept of bracketing (although maybe there aren't enough breakpoints to make the idea worthwhile)?

Bill

[edwardc]

... Due to lack of strainer we then found and removed a healthy clump of seaweed salad in the raw water access port on the heat exchanger, ...

...Blockage in the seawater tubes of the heat exchanger? We poked around with a narrow screwdriver but didn't find much. ...

Given the stringy nature of that seeweed, I suspect that your tubes are clogged with it. A screwdriver isn't enough. You will need to remove the access plate at the other end of the HX and rod-out each and every tube using a long stiff wire. I found that a straightened wire coathanger works well.

[capnward]

I was going to ask "What is bracketing?", but I think edwardc just gave us a good example. I've been wondering how you guys do that.
Anyway Dave, since removing the seaweed salad from the HX intake did not resolve the issue, and you seem to have good flow out the back, it is also possible you have a FWC problem, not raw water, and need a new impeller in your Oberdorfer. Clean out your HX, but I would check your fresh water impeller first. The FWC problem may have been caused by the raw water obstruction, if your fresh water boiled over because of restricted raw water flow, and you didn't replenish it, then your impeller broke from running dry. That will be easy to discover. The impeller could still get brittle after years of sitting still. Have you been turning the grease cup before running it? Maybe there is a blockage where the coolant exits the manifold. That blockage may be parts of the broken impeller. If you blow into the hose from the pump to the water intake plate, and your eyes bulge out from too much resistance, that's another way of knowing if you have a blockage, either in the t-stat or, more likely, the manifold exit.
A coolant leak is very possible, even likely. It may be that it boiled over because your coolant ran dry and damaged the impeller. Boiling over will still leave enough water at the impeller for it to work after a coolant refill, if the impeller is not damaged. That happened to me a few days ago. My raw water pump seized up with belt screeching because I neglected to fix the leaking seals, and the bearings got shot. It still turns with effort, hopefully the shaft isn't shot as well, but it probably is. So after removing the belt, I limped home by running on the fresh water alone, watching the temperature and turning it off after a minute or two, as it approached boiling point. After waiting a while I removed the hot HX cap with a hot pad, and then some coolant water boiled out. I filled it with fresh water and ran for a few minutes more. Luckily I wasn't far from the marina, so I only repeated that process twice. The new pump is on its way, $307 later. I also ordered parts to fix the old one, so I will have a working spare. Monitor both your water pumps for leaks regularly. Always check coolant level in the HX before starting.
PS: After looking at the photo of the Oberdorfer pump, I noticed wire hose clamps, and extensive rust under the pump. I would use these kind of hose clamps:

https://moyermarine.com/product/stainless-steel-hose-clamps-for-12-to-58-hose-ohsp_

It may be those wire clamps been leaking, and the engine running for years with a low coolant level, wearing out the impeller quicker. Or the clamps may be perfectly tight.

[Administrator]

Bracketing as defined by the DoD.

Bill

[Dave Corning]

Clean out your HX, but I would check your fresh water impeller first. The FWC problem may have been caused by the raw water obstruction, if your fresh water boiled over because of restricted raw water flow, and you didn't replenish it, then your impeller broke from running dry. That will be easy to discover. The impeller could still get brittle after years of sitting still. Have you been turning the grease cup before running it? Maybe there is a blockage where the coolant exits the manifold. That blockage may be parts of the broken impeller. If you blow into the hose from the pump to the water intake plate, and your eyes bulge out from too much resistance, that's another way of knowing if you have a blockage, either in the t-stat or, more likely, the manifold exit.
A coolant leak is very possible, even likely. It may be that it boiled over because your coolant ran dry and damaged the impeller. Boiling over will still leave enough water at the impeller for it to work after a coolant refill, if the impeller is not damaged.
...
Monitor both your water pumps for leaks regularly. Always check coolant level in the HX before starting.
PS: After looking at the photo of the Oberdorfer pump, I noticed wire hose clamps, and extensive rust under the pump. I would use these kind of hose clamps:

https://moyermarine.com/product/stainless-steel-hose-clamps-for-12-to-58-hose-ohsp_

It may be those wire clamps been leaking, and the engine running for years with a low coolant level, wearing out the impeller quicker. Or the clamps may be perfectly tight.

Thanks for the insights!
Well ... the coolant pump impeller was missing 6 of 6 pieces! Before we disconnected the pump we ran for a few minutes and didn't find any noticable coolant leaks.
Sadly, only 5 of 6 bits were retrieved. Struggled to remove the hose directly following the pump, but we only took the access plate off the pump,I suppose we have to remove the pump from the flange just to access to the hose?

Replaced coolant with water and the temps were running much much better but did start to climb over 160 toward 180 after about 15 mind, could that be tied to using water vs coolant?
How critical is finding that impeller bit...?
We'll check the manifold exit next, and replacing hosing and clamps by next spring.
Also, the grease cup is getting filled asap and worked in to our operating procedures.

Any more suggestions are welcome!
Thanks,
DC

[ndutton]

Finding the sixth impeller bit is important, perhaps even critical. Hang in there. Further having seen the amount of seaweed you're pumping through, consider adding a raw water strainer ahead of the heat exchanger.

[edwardc]

Those impeller bits tend to lodge in elbow fittings, as they are usually the most resrticted part of the flow.

Start with the first elbow downstream of the pump, and work your way downstream until you find it.