Closed water system and Stator cleanliness

[Dave in NC]

Good morning,
After replacing the lower unit water pump, I am still having problems with engine water temperature in my 1987 3.7, 224 cid, 185 hp Mercruiser. The gage is not responding.
I removed the thermostat and the temperature sender. The thermostat was stuck mostly closed(about 1/8” open). The sender was tarnished, but otherwise in good condition. I removed the thermostat from the system( I will install a new one later), cleaned the sender(I have ordered a new one) and buttoned everything back up. Removed the heat exchanger inlet, started the engine. I had minimal flow (I’m guessing). Just spitting out.
Removed the circulating pump cover and inspected the impeller. Looks good, almost new I would say. I am getting set to start flushing the system looking for clogs.
If you have experienced this, or can recommend some areas to check, I would be grateful.
Also, how clean should the alternator components be? The magnets are still tightly adhered to the dampner and the stator looks clean except for slight discoloration. Should I clean beyond normal system cleanliness before reassembly?

 

[Bondo]

Removed the heat exchanger inlet, started the engine. I had minimal flow (I’m guessing). Just spitting out.

Ayuh,.... Welcome Aboard,..... That, ^^^ is a problem,....

The raw water pump should push a solid flow of water, enough to bubble up 4 or 5", when holdin' the hose vertical,.....

 

[Bt Doctur]

You start at the impeller in the outdrive especially if no water is getting to the heat exchanger

 

[Dave in NC]

That’s what I was thinking. I am going to start by flushing the head and work my way through the system.

 

[Dave in NC]

Thanks BtDctur, but I just got done replacing the pump in the outdrive. I do have good flow now from the transom area. Iam currently trying to run down a low flow problem in the closed system.

 

[Bt Doctur]

Removed the heat exchanger inlet, started the engine. I had minimal flow (I’m guessing). Just spitting out.

The heat exchanger "inlet" is where the water enters coming from the outdrive, the exchangers "exit" is where it commects to the elbow. . Being a closed system you wont see the AF flowing . The normal temp for a FWC motor is about 170 Deg.

 

[Bt Doctur]

click to enlarge

 

[Dave in NC]

Thanks Bt Doctur. Just so I have the system interrelationships understood correctly - The engine is a “closed loop”. It enters the heat exchanger on the aft end, on the outside of the exchanger tubes, then returns to the pump via the inlet manifold, and the L/O cooler where it starts the cycle again. Through the head, exhaust manifold and back to the heat exchanger.
The pump on the outdrive(the “pickup pump”) routes water from wherever the boat is running to the forward end of the heat exchanger, through the inside of the exchanger tubes, exits aft, then through the power steering cooler, into the exhaust elbow and back over the side.
Am I thinking right? If so, how much flow should I see from the closed loop system?

 

[Scott Danforth]

the impeller in the outdrive will provide up to 20 GPM, that is filling a 5 gallon bucket in about 15 seconds or so. at idle, it should take about 20 seconds.

 

[Dave in NC]

Thanks Scott. What about the engine pump? How much water flow from there?

 

[Scott Danforth]

about the same (same impeller on the platypus motor)

However as others indicated, unless you tear into the cooling system and run it without coolant (dont do that), you cant see the glycol water flow

If you are over heating (and in that motor, anything more than 170 is an overheat)

first place to check - raw water pump in outdrive.
if that impeller had missing vanes.... you need to find them, that means tearing your system apart including pulling the end caps of the heat exhcanger off

second place to check is if the glycol is low (from the cam shaft nose that drives the circulating pump)

third is head gasket. if the temp got much over 170, the 470 motor will spit its head gasket out like a toddler eating broccoli

4th is if the heat exchanger is plugged (pull the end caps and look, you should be able to see thru each of the tubes. tube id is .204" or so, so a 3/16" riffle brush will work

5th place is if the thermostat is either stuck shut (no flow) or stuck open (too much flow)

 

[Dave in NC]

Ok, thanks, Scott. I will check all those areas.

 

[Dave in NC]

Good Morning, all,
Current progress: Flushed water through the head via the water pump outlet. Had some rust discoloration flush out through the exit connection, but overall a good flow. Back flushed the inlet manifold. Good flow. Once again some rust discoloration, but no large amounts of debris. Removed the heat exchanger. Soaked it in a mild TSP bath for a day. Flushed. Had some debris flush out via the shell side. Small pieces of rust, etc. The tube side is clear. All tubes clear.
Current plan: Continue flushing system including the steering cooler, and exhaust elbow. Flush the hose going to the inlet manifold. I have received the new water temperature sender. Expect the new water pump gasket set Saturday and new thermostat Sunday.
I have a question about the thickness of the gasket on the water pump. When I pulled the front cover off and cleaned the gasket surfaces I noticed that the gasket was pretty thick. I measured it. The old gasket, compressed, was 0.071". I am thinking that would indicate that the gasket was probably 1/8"(0.125") when installed, new.
Is that the correct thickness? I know that on some pumps, not necessarily pleasure boat pumps, gasket thickness has an effect on water flow/pressure. Does anyone know the correct thickness of the gasket that should be installed. I will measure the new one when it arrives Saturday.
Also, the installed "radiator" cap installed in the system is 7 psi. Is that normal? What should the correct pressure be? I feel that 7 is a low number, but haven't noticed any increase in the reservoir.
Thanks to all for the help and guidance so far. Hopefully plan on taking a cruise THIS summer!!

 

[Scott Danforth]

there should not have been rust in the shell side unless someone didnt have the glycol % high enough

7psi is about right. mostly because the iron head on the aluminum block

is this the original 3" heat exchanger or the upgraded 4" heat exchanger?

 

[Dave in NC]

I think it is the 4”. I’m at work right now, but I’ll check later today.

 

[Bt Doctur]

overheating is either a water in /water out problem . What condition is the exaust elbow in?

 

[Scott Danforth]

overheating is either a water in /water out problem . What condition is the exaust elbow in?

on the 470, it could also be a bad head gasket

 

[nola mike]

The operating temp is <210', and the cap should be 14 psi.

 

[Dave in NC]

It’s the 4”.

 

[Dave in NC]

Bt doctur- I haven’t had the exhaust elbow off - YET. Are you suggesting that the exhaust elbow may be clogged?
Scott - PLEASE, let’s hope it’s not that!!! But do I have a 470? Identifying boat engines is a very confusing effort. The plate on my engine says MCM485, 224 cid, rated horsepower 185, W.O.T. 4200 - 4600. What engine DO I have? If it WAS a bad head gasket, wouldn’t I have some indication of that like excessive oil consumption or a oily film out of the exhaust?
Nola Mike - Welcome and thanks for the input! But now I am confused. I was told that 7 psi is a good pressure.