I am assembling a new block from a truck engine and I need to know which or both of the oil bypass valves need to be replace with the marine valves? I noticed today that there is one in the center and one off to the side. I ordered 2 of the part # 34543 thinking I would have a spare for my stroker motor. thanks

http://www.offshoreonly.com/forums/g...fs-bypass.html

If both of your lines are connected to the oil filter adapter you only need the outside bypass and not the center one. I'm not sure where you got that part number from, but the 30lb oil bypass valve is GM part 25161284.

I got it from here, I am trying to figure out if it is the same or not. my oil system is a sandwich style oil thermostat with the 2 lines running from it to a 18" cooler and I run the filter right off of it with no remote mount

http://www.ebay.com/itm/160958260089...84.m1497.l2649

Then you only need the one bypass on the base pad. I would want to see the Mercruiser cross reference part number, but the description appears to be right. For $10 you don't want it to be the wrong part.

I cant seem to find anything to tell me the cross reference. if I cant be sure then I will be buying another one form the parts store

so just to be clear, the center one is ok as is, the outside one on the pad is the one I need to swap out? can anyone tell me if the 2 taps next to the filter that are for the cooler on a truck but plugged on a marine engine would be a good spot for a oil temp sender?

Remove the one in the center. Put a 30lbs valve in the outside location. I buy my 30lbs valves at H&H for less than $10 in stock. The 2 taps on the outside are two small too support a marine oil cooler.

What 28Eliminator said. That valve is available from GMPartsDirect for less than $4. And as BigJim said, you need to remove the center one - that is only used if you want to direct oil to the remote cooler ports on the block. Leaving the valve in place forces oil to make several sharp turns before hitting the main bearings.

Any Chevy dealer can order the bypass valve and have them in a few days. As 1BIGJIM said remove the center one. It routes the oil to the 2 rail ports and around a couple of 90s. If you were using those rail ports you would want the center bypass. It is easy to see what happens when you have the motor apart. You could use the port for oil temp, but I'm not sure how fast it would react to a temp change because the oil won't be traveling past it all the time, so I probably wouldn't trust it as being acurate.