Repowered with Automotive engine

[twinscrewzz]

So bought a 21 footer that had been garaged for the last 7 years. Repowered in 2006 1 year on the water then garaged.

Going though the invoices provided by the PO. engine serial number 2499529 EMR. 5.7 290HP @5100 RPM.
Bargain hot rod motor not Marine.
Now on to my questions.

What thermostat should I run? Raw water cooled
Marine motors 140 to 150
Auto 240? Can't run ray water at 240 So 180?

What is the difference between the marine 350 and automotive 350? All accessories transfered over from the original mercrusier.

Figure I'd run it till t grenades then put in a marine motor.

looking or any thoughts n the automotive motor first
then
When time who do I look to for a new long block?
thanks In advance for input
Mike

 

[BillK2632]

Thermostat: Most current Mercruisers run a 160. Some older ones run a 140.

Differences between an auto and marine 350: Hard to say, I had always heard that the marine version was basically a truck engine - 4bolt crank and cams designed to provide more low end torque vs high end horsepower. Pretty sure other than marinizing the cooling, ignition and fuel system, the block is unchanged from what comes out of the GM plant - same 350 block that when in a Chevy truck. Of course with Mercruiser starting to build their own engines now (the new 4.5 V6) it's a different game.

 

[Bt Doctur]

If its the same one as in your signature I would not be putting that much money into it. Stringer parts are very hard to find.

 

[NorCal Boater]

One of the main issues in the block is the soft/freeze plugs. In a car engine they are steel, in a marine engine they're brass. The brass is resistant to corrosion in salt water but since you are in Phoenix and boating mostly in lakes it may not be a problem for a while.

But, as stated above, your bigger problem is the out drive. The OMC stringer drive was a POS parts are becoming non-existent.

 

[twinscrewzz]

Nope Not the stringer. walked away from that nightmare.
This question is on my center console fishing boat.
I'm currently looking at a 86 340 dancer. Always had IO's so have to get educated on V drives. But that is another thread.

 

[Bt Doctur]

a block is a block, nothing special, the cam is the most critical component need good HP with low exaust reversion qualities.
brass core plugs, spark arrested components.

 

[twinscrewzz]

a block is a block, nothing special, the cam is the most critical component need good HP with low exaust reversion qualities.
brass core plugs, spark arrested components.

As mentioned Marine accessories so spark arrested components.
290 HP @ 5100 rpms
326 Ft. Lbs. @ 3750

Had it on the water and runs 35 MPH at 3200 rpms. started running hot so replaced impeller.