1999 5.7GXI with DuoProp, oil cooler & Water Pressure

have 2 questions:
1. I have added an inline oil cooler, does someone have a diagram showing what water hose it should be installed on?
2. What water pressure should I expect to see at 800~2000RPM on muffs. Also what should I expect when the boat is in the water running across the lake at 1000-5000RPM
3. how do I recognize if a impeller pump housing is worn out.


The reason I ask:
I installed it in the incoming hose, originally going from the outdrive to the power steering cooler then to the sea water impeller pump. Now it goes from the outdrive to the power steering cooler, to the oil cooler, then to the sea water impeller pump.


I had an overheating issue the last time I took it out, when I got home I found the impeller was completely destroyed. I replaced it , pulled the 1/4” plug out of the water neck, and while testing it in the driveway with muffs it was not producing enough water flow to push it out on the water neck plug hole and none coming out the exhaust. I did not like the condition of my muffs, so bought some new ones with a 2 sided hose connection, but no help.


To make sure the system is not pulling air, with a smoke generator, I tested the entire water passage/hose from the pickup in the outdrive to the pump and no leak.
Using a garden hose, I flowed water from the pump to the outdrive, it flows well and seemed to not have any restrictions.


Today, without any other ideas, I decided to remove the oil cooler from the incoming hose and replace it with a piece of 1”PCB. I ran it on the muffs again and got a light stream of water coming from the hole in the waterneck, not much, but water is coming from the exhaust. I plugged the hole with a 10 psi gauge and let it idle for a while, it did not overheat. I saw bounce ~1PSI at idle, in up to ~3PSI at ~2000 RPM.


I have a new impeller and new impeller pump housing, I will probably still install these to see if the pressure goes up.


I guess I need to find a new home for the oil cooler, I’m baffled by this because it has plenty of flow threw it.


im very interested in feedback and any help. Please ask if you have questions.

1) I don’t think the rectangular muffs seal well; I had trouble with them as well; the best I used was the Merc/Quicksilver round ones with the metal rod clamp. The rectangular ones use rubber that is too stiff to conform to the shape of the lower unit.
2) I’d try to find out if Volvo used an engine oil cooler and how they plumbed it. I don’t recall ever seeing one on a small block V8 but the big blocks did come with them; see if you can find a parts diagram.
3) I don’t think in most cases the engine oil cooler is 100% necessary if you are using correct motor oil. Use the Merc 25/40 syn blend or a straight 30 syn oil for best protection. I would not use a car based 5/ or 10/ anything.

ditto per louc... additionally, did you find or account for all the pieces of the old trashed impeller??? On MERC BBC marine conversions with engine mounted raw water pumps the oil and trans coolers ( or P/S) is usually on the output side of the raw water pump not the suction. This has the added benefit of having the cooler act as a "catcher" for water pump fragments.... which can be flushed out by temporarily plumbing a water hose ( at street pressure) to the raw water outlet hose on the heat exchanger ( before the elbows).... with water pump outlet disconnected of course. Put hose that went to the raw water pump in a big bucket to avoid a mess and collect impeller pieces.

Thanks for the feedback.
I do believe I found all the old impeller parts, I at least found a lot of them.

Any feedback on what water pressure I should expect at the neck?

I added the cooler because the 5.7 has been upgraded and makes 400HP.

Any feedback how to recognize a worn out raw water pump housing?

Goggle the PDF document “Volvo Penta Overheat Diagnosis” it covers all the causes of overheating on these and how to test for correct vacuum & pressure in the cooling system.

PS why don’t you try running it like you usually do and take an IR temp gun with you; run it up on plane and take readings of your oil filter and oil pan. If they are below 250*F I don’t think you have to worry. What is your hot slow idle oil pressure reading? Normally on my old engine (33 years old never rebuilt short block with reman heads added 4 years ago) I get about 25 lbs and then as the engine cools off it will rise to 40 psi. If you are getting 20-30 psi at slow idle after dropping off plane your oil is not getting too hot most likely. You can also do an oil analysis, use a straight 40 oil or go with full syn oil. I would do some diagnostics to see if the cooler is really needed. As I said the big block VP engines did use them probably because they were in heavy boats.