Sporadic cooling 160-200+, back to 140

[Guest]

Sporadic cooling: 200+ down to 125, no thermostat or with thermostat. After flushing and checking every hose and fitting.

Good water floor then no water flow: Any ideas what this is caused by? I have now installed the new aftermarket thermostat so i will see if this persists.

Chain of events:
I change the exhaust last year from the engine manifold back. New exhaust flange, new brass fittings, new water lift muffler, new exhaust hose.

The system ran at 160 with the original thermostat and then started going up to 200 and the water flow shut down to a trickle. I stopped the engine, let it cool for 1 to 20 minutes and sometimes it would go back to 160 and water flow would be normal.

The problem can always be initiated by disconnecting the raw water and connecting to a bucket of water. After reconnecting the raw water the overheating persists. Sometimes running at idle but often a high RPM can initiate the failure to flow and then 200 F. Sometimes the flow is nothing and sometimes just 1/2 a cup every 10 seconds.

Ran with no thermostat and the check valve and restriction in place. Still the same problem. Replace water pump impeller and checked all parts. All water pump parts are OK, greased and fitting snugly. Checked every hose, every fitting and flushed the cooling system with 30 PSI water. Got a nice bucket of rust out of the water jacket side on reverse flush. Still the problem persisted.

Every time I disconnect the raw water and connect to a bucket of water there is no flow. I primed the hose with water, I tried pushing water into the intake hose with 30 PSI hose. No flow and no water moves in the intake hose. I check every opening in the system from the intake hose to exhaust exit on the transom. All seem very clear.

Reconnected the raw water, and sometimes it starts to work.

I Changed to new aftermarket thermostat with spacer. Seems to run fine at idle and under load (150-160 idle and 170/180 under full throttle maximum load). Ran out of time so I didn't repeat the use of a bucket of water.

I had been through every single hose and fitting to make sure there were no restrictions. The impellers have never had a chip off them and

I replace every 1-2 years since rebuild. What would cause this?

Is there some way a gas/steam pocket can form and block flow?

jimB

[ndutton]

My instant thoughts without thinking it through thoroughly:

Thermostat function should not affect the water flow out of the exhaust. The thermostat either sends it through the engine or bypasses the engine. It's clear you have a flow issue, either it's not getting pumped or it's not getting out. Your test in the bucket suggests you're good up to the pump.

Can you correlate the temp/flow fluctuations with the replacement of any particular part? Like the impeller? There has been some discussion around here over a new crop of impellers that aren't as thick as before and concerns over them because impellers need to seal against the pump faceplate to function properly. The shorter impellers may not be sealing properly. The jury's still out on that one.

[Side note: haven't heard back from Baltimore Sailor on the resolution of his impeller concerns.]

The proper impeller thickness is 0.875"

There has been further discussion over worn cam shoes inside the pumps too.

All of this assumes the passages, hoses and fittings are in fact clear as you report.

[roadnsky]

Jim-
When you got the "bucket of rust" when flushing, did you get consistent CLEAR water after that?
Have you flushed the manifold too?

[Concord]

Thermostat

Jim,
When you upgraded the thermostat did you install the check valve kit to create a pressure drop in the bypass line? Without the check valve kit the engine could run hot because the flow could go through the bypass even when the thermostat is fully open.

I recently had a very similar experience with Concord, we had no flow when the thermostat was closed then we would get bursts of flow when the thermostat would open then nothing. We found that we had a clog in the thermostat cap on the water pump side. We could not see the clog without removing the fitting from the cap as the hose barb side was clear and the clog did not extend far enough into the cap to be visible.

The new style thermostat will mask this because the new style thermostat has a small hole drilled in the disk to keep a small flow through the jacket even when the thermostat is closed. Below is where we documented the clog and subsequent repair. The initial clog grew into a bigger issue.

http://www.moyermarine.com//forums/showthread.php?t=4164

Good luck

[hanleyclifford]

Have you looked at the thru hull where the raw water enters (also the strainer)?

[thatch]

JimB,
One thing that I haven't seen mentioned yet is that it is possible that the raw water intake hose is collapsing under suction. Bear in mind that these hoses normally have an inner and an outer layer and that although they may look good on the outside they may be collapsing on the inside. Ironically, the better the rest of the system is flowing, the more suction is placed on that hose. The easiest way to check that part of the system is to disconnect the existing hose at the water pump and replace it with a different hose run into a bucket full of water and see how the problem reacts.
Tom

[rigspelt]

Sporadic cooling: 200+ down to 125, no thermostat or with thermostat. After flushing and checking every hose and fitting.

I changed the exhaust last year from the engine manifold back. New exhaust flange, new brass fittings, new water lift muffler, new exhaust hose.

Do all the new parts have physically the same dimensions as the old exhaust system? I always wonder about the last change to an engine when a new problem develops.

The system ran at 160 with the original thermostat and then started going up to 200 and the water flow shut down to a trickle. I stopped the engine, let it cool for 1 to 20 minutes and sometimes it would go back to 160 and water flow would be normal.

The problem can always be initiated by disconnecting the raw water and connecting to a bucket of water. After reconnecting the raw water the overheating persists. Sometimes running at idle but often a high RPM can initiate the failure to flow and then 200 F. Sometimes the flow is nothing and sometimes just 1/2 a cup every 10 seconds.

Every time I disconnect the raw water and connect to a bucket of water there is no flow. I primed the hose with water, I tried pushing water into the intake hose with 30 PSI hose. No flow and no water moves in the intake hose. I check every opening in the system from the intake hose to exhaust exit on the transom. All seem very clear.

Reconnected the raw water, and sometimes it starts to work.

I can't quite get this clear, so can you check that I have this right?:
1. The overheating will occur intermittently and apparently unpredictably (no clear pattern) while the raw water is hooked up normally, is that right?
2. When you switch to a bucket of water from raw water there is no flow from the transom, is that right?
3. Overheating always occurs when you switch back to raw water, but water comes out of the transom and then sometimes the temperature will normalize, is that right?
4. Have you checked for water flow anywhere other than at the transom, to see where in the system the diminshed flow problem starts? Thatch and the others have given examples of intermittent restrictions at various places from the raw water intake onward.

I Changed to new aftermarket thermostat with spacer. Seems to run fine at idle and under load (150-160 idle and 170/180 under full throttle maximum load). Ran out of time so I didn't repeat the use of a bucket of water.

1. Did the problem seem to resolve with the new thermostat and spacer?
2. What was the condition of the thermostat housing and boss (thermostat seat)?

Is there some way a gas/steam pocket can form and block flow?

Based on my reading through the archives over the past couple of years while learning the A4, I did run across some threads that talked about air pockets forming in the cooling system in various ways. One poster installed a bleed valve on the brass elbow at the thermostat end of the manifold to deal with his problem. Being an amateur however I am not sure if this applies to you, and why it would be intermittent, if it is even happening in your case.

[JimB]

Thanks to everyone and the suggestions.
I will need to check this next weekend. I live in MA and sail in Maine.

I think the most likely culprit is a piece of something (a large flake of rust) that intermittently gets caught someplace.
The air pocket sounds interesting but makes no sense.

Most likely?:Perhaps when the hose is removed from the water pump intake the back flow of the water pulls something into a restriction position. Then randomly turbulent flow pushes it out of the way. Maybe at season end I will remove the water jacket plate.

I installed the bypass restriction house as indicated in the instructions. The valve is in place and it seems to make no difference if the manual valve is shut or open when there is overheating. When the engine operates normally the valve can slightly alter the temperature.

I did flush both the water jacket and manifold until I got only clear water. The rust was from the last 7 years, so that would be about a teaspoon per season of rust.
I removed every hose and used a wire to check every fitting and looked inside all openings such as the manifold to check for any restriction.
The new thermostat seems to run great (for 15 minutes anyway) so I will see what happens.

I would say I am about 16 hours in this problem so I will focus on sailing.
So far this problem is only an annoyance and eventually clears.

I enjoy working on the engine but the wife does not. She just has to understand that all 1 hour jobs take 2 to 4 hours and 3 hours jobs take all day.When bolts, studs or nuts are involved assume one will strip, one will break and the one tool you need is at home. However, if you order on Monday from Moyer Marine the parts are always in right on time.

The most odd thing is this all started when I rebuilt the exhaust system. I thought is could be a restriction in the exhaust and manifold, but I checked every hose, flushed them all and even looked in inside the Vetus water lift muffler.