Oil gets too hot and I'm losing my oil pressure in idle.

I have a 3.7mercruiser 190 hp and the engine got rebuild 2 year ago. Oil is HD 40. Engine temp is 160 F. I get the problem after 1 hour on the water

My problem is that I am loosing my oil pressure in idle, when it is a hot summer day 100 F and the water is over 80 F.


At idling (600 rpm) I have 3-5 psi. (800 rpm) I have 15 to 20 psi. (1000 rpm) I have 60 psi

I thought of installing an oil cooler, but I'm afraid I will lose some of the oil flow and I have no way to check up on it.

When I look at the intake manifold there is a oil cooler ( or heat up the engine fast ), I can see that the hot water is passing through the manifold to warm it up and keep it the same temperature as the engine.

My idea is that if I let the cold water from the stern drive go through the manifold to cool it down and keep the oil cold, I Will be able to hold my oil pressure.

Will it be a bad idea or will it create other problems ?

Thanks Steffen

Re: Oil gets too hot and I'm losing my oil pressure in idle.

not sure what your problem is but you have to remember as the oil heats up it thins out. when you first start your engine you have a thick oil as the engine gets hotter the oil thins out and now you have less pressure. for example on my boat start up 60psi 600-800rpm, 80psi 1000 - 3500rpm. when motor hits operating temperature 15-20 psi 600 - 800rpm, 40psi 1000-2000rpms, 3500+ rpms 60psi. other thing to look at is make sure your oil pressure gauge is working right and make sure the oil pressure sendor/sensor is working and make sure the oil pump pickup screen was cleaned after rebuild

Re: Oil gets too hot and I'm losing my oil pressure in idle.

All sounds pretty normal for a 470, 3-5 psi at 600 rpm idle is plenty as long as it quickly builds pressure as the RPM's rise, and yours does. I dont see any problem here. Mine has been doing this for years. I wouldnt worry about it at all.

Re: Oil gets too hot and I'm losing my oil pressure in idle.

Thanks for your help
I thought I had a big problem. It makes me nervous when I see the low pressure at idle. I've spent a lot of money on my engine and do not want something go wrong.
Thanks for the quick response.

Steffen