I need a crash course on engineering....

[brico]

Forgive my ignorance. I am not and engineer but have been with ships and boats all my life. I am trying to understand the flow of coolant in my 1980 DD 6-71 naturally aspirated engines.

1.) I fully understand the raw water flow from the raw water pump, through the fuel oil cooler, then through the middle of the heat exchanger expansion tank and then along the back of the engine into the stainless steel elbow exhaust pipe and overboard.

2.) My engine oil cooler assembly is on the front inner end of the engine with the coolant pipes entering it in the bottom and exiting in the top.

3.) My MG506 transmission oil is cooled by high pressure oil hoses entering and exiting the bottom of the heat exchanger. Not sure which one is in and which one is out, but at this time i do not care.

4.) My heat exchanger is not a typical GM heat exchanger but i believe J&T modified/marinized one.

5.) The coolant exits the thermostat housing, runs along the engine and enters the top of the heat exchanger and drains down over the heat exchanger core getting cooled in the process.

6. The somewhat cooled coolant exits the heat exchanger at the bottom and enters the bottom of the engine oil cooler and exits the engine oil cooler at the top and enters the suction side of the centrifugal fresh water/coolant pump which discharges / pushes the water into the engine block etc.
7.) The fresh water/coolant runs across various cavities in the engine block etc and enters (in my case) through four openings into a water manifold and repeats the circle from point #5. This of course is when the coolant temperature is above certain limit when the thermostat opens and lets the coolant through.

8.) While the engine is warming up and the thermostat closed (is it really fully closed?) the coolant is discharged/pumped by the fresh water pump through the engine block etc. and enters the water manifold and is directed with a "bypass" hose into exhaust manifold and from the exhaust manifold via another "bypass" rigid metal pipe into the top of the engine oil cooler assembly.

I believe I have figured out the flow direction here....

The questions I have are:

A) Is the thermostat tightly shut and all of the coolant flow goes via those two bypass hose, exhaust manifold and bypass metal pipe at the start of the engine or is it letting some water through?

B) When does the flow through the heat exchanger actually start as I noticed the water heating up in the pipe coming out of the thermostat housing at temperatures below thermostat opening temps?

C) When the thermostat is fully open, does its assembly still let some water enter the exhaust manifold and exits it and goes to the top of the engine oil cooler as it does when engine is cold and thermostat "closed?\"?

D) For the period while the fresh water/coolant is not passing through the heat exchanger to cool down, it is also not cooling the engine oil as there is no any (or much flow of water) through the engine oil cooler, guess the oil hasn't heated up enough to need cooling until the water/coolant temperature reaches the thermostat opening temperature?

E) How is the transmission oil cooled? I guess it is just a pipe passing through the bottom of the heat exchanger expansion tank, from one side to the other, or is there a more elaborate heat transfer assembly in the expansion tank?

F) If i decide to remove the entire heat exchanger expansion tank for de-rusting and cleaning i will have to disconnect the transmission hoses at the bottom. These are higher than the transmission so i guess I will not have to drain the transmission oil system?

Your comments on each or any points above are much appreciated.

Petar

[workingonadream]

yes you have to disconnect the tranny lines, and they are high enough that you shouldn't have to drain the system, you might see a little loss though. as for the other questions, why do you ask. are you having overheating problems, running hot, or not coming up to temp etc. my old adage is if it aint broke don't fix it

[Blaine Thorpe]

The thermostat is there to direct flow. When it is closed, it directs flow back to the jacket water pump inlet. When it is open, it directs flow through the heat exchanger then to the jacket water pump inlet.

As the engine starts to warm up, it will split the flow to the JW pump and heat exchanger. The flow through the engine (from the jw pump through the engine then to the thermostat) is the same regardless of the position of the thermostat. There are usually two specs on a thermostat, opening temperature and full open temperature.

Also, the oil pressure going to the transmission oil cooler should be low pressure. There are two different pressures in the transmission. High pressure for the clutches, and low pressure for the bearings. Without seeing the transmission oil cooler, I can't tell what type it is, but assume that is a tube and bundle type, with oil flowing around the tubes, and water flowing through the tubes to provide the heat transfer.

[brico]

Thanks guys. I looked at the manual and found some more info on thermostats. I believe i have the "non blocking (choke or poppet) type thermostat fitted hence the flow of coolant through the bypass and normal coolant line going to the heat exchanger.