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Tan, MerCruiser Certified Technician
Category: Boat
Satisfied Customers: 11073
Experience:  40 yrs. experience with complete engine repairs both inboard/outboard and MerCruiser Certified Technician.
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I am looking for a diagram for closed cooling system. it

Customer Question

I am looking for a diagram for closed cooling system. it needs to include block and exhaust manifold. my application is a Mercruiser 165 HP inline 6 engine. the thermostat housing and any fittings description would be helpful.thanks
Submitted: 2 months ago.
Category: Boat
Expert:  Jason replied 2 months ago.

H​I Chris, my name is***** read what you wrote. The best/only diagram for this engine is going to be in the factory service manual. Have you not seen that diagram yet or have you already seen that one, and were looking for something different?

Customer: replied 2 months ago.
I did look at the service manuals and it seems they are only a half system, also the thermostat housing is not clear on how the hoses/ fittings should look like. maybe a better approach is how the general flow should look like.
for example on the antifreeze side of the cooling system the water pump mounted to engine block connect to large hose on exchanger. then the 2 ports on top of stat housing does 1 go directly back to return side of exchanger ? and the other go to front of manifold then from at the back of manifold it returns to an additional port on exchanger?
Customer: replied 2 months ago.
this is the stat I have
Expert:  Jason replied 2 months ago.

Hi Chris. Good morning. I've spent the last 15 minutes flipping through all of the service manuals and nothing matches that thermostat housing. Where did you get that picture from? Also, what do you mean by a half system? All Mercruiser engines are half systems. Does your engine have some kind of aftermarket brand of closed cooling on it?

Customer: replied 2 months ago.
I bought the stat housing from go to marine P/N 861493A3. its basically the same as OEM, the only difference I can see is the larger thermostat. the exchanger doesn't appear to have any branding on it, however it looks like the typical crusader V-8 style 2 horizontal tanks joined together. given the physical size of the exchanger, it should be able to cool manifold and block. the engine will be used exclusively in salt water so In an effort to reduce corrosion it should cool the manifold as well. to my knowledge you are right Mercruiser does not offer a full system but most aftermarket companies do. I guess the answer will be complicated, because the engine is pretty old and Mercruiser never documented anything with the full system . I was hoping to use the common V-8 full system diagram and apply it to my it not recommended to run a cooler for an exhaust manifold even in salt water
Expert:  Jason replied 2 months ago.

Now I'm really confused. Part number 861493A3​ is not for a straight 6 engine. That housing is for 3 liter engines years 1999 and up with open cooling. What makes you think this thermostat housing is for your engine?

Customer: replied 2 months ago.
sorry, some how when I was looking for the housing that part number came up. if you have a recommendation for the correct unit
Expert:  Jason replied 2 months ago.

some how when I was looking for the housing that part number came up​

​I can't say other than when you look parts up in the mercury dealer network the parts will always be correct. When you look parts up on various websites, they can be full of errors. What is the serial number on your engine, I will look up the correct part number for you.

Customer: replied 2 months ago.
i'll get that asap. it is from 1980 though, if that helps any
Expert:  Jason replied 2 months ago.

Mercury doesn't catalog anything by year, it's all done by serial number.

Customer: replied 2 months ago.
serial #3290021
Expert:  Tan replied 2 months ago.

Hello. My name is Tan.

Here is a link to the closed cooling parts for your motor.

The components you show are not correct for this motor.

Here is the closed cooling system diagram for that motor.

Customer: replied 2 months ago.
I actually have that diagram, it only indicates closed cooling for engine block, maybe pictures are a better solution to see how a full system is hooked up as for all of the images I could find in books and the web are so old and blurry I cant even tell if im looking at an oil pan or valve cover lol.
is running a "FWC" manifold really that unconventional in salt water?sorry to beat a dead horse
Expert:  Tan replied 2 months ago.

No that's when you want to run closed cooling this keep salt water out of the engine. The manifold has to be run with the raw water.

The closed cooling only run through the engine block. The raw water runs through the heat exchanger and the manifold.

In this diagram red is raw water and blue is closed cooling coolant.

So what is it you need to know that is shown in this diagram?

Customer: replied 2 months ago.
ok so the manifold is the sacrificial part and is designed to be replaced every 3-4 years?
I just thought it odd that almost every marine engine today has a full system available V-8, and V-6
the diagram is clear on how to route everything I think the only omission is my system has a raw water pump mounted to the engine block so that takes place of the pump normally located in the outdrive
Expert:  Tan replied 2 months ago.

Correct the raw water pump supplies water to the heat exchanger.

I hope I’ve provided the information you were seeking. If you are happy with my service, your 5-star rating at this time is most welcome. If you need more help, please let me know so l can continue to assist you.

Thank you......Tan

Customer: replied 2 months ago.
ok thanks
Expert:  Tan replied 2 months ago.

Your welcome..........Thank you....Tan

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