oil bypass valve question on gen VI engine
 

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

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.

what is the most ideal place for a oil temp sending unit? I would like to have this installed before the engine goes back in

part #25161284 ordered. if those other 2 end up the same than I guess I have spares

will it hurt anything if you leave the truck valve in ?

Technically no, as merc leaves them in, but if you take a look at your block you will see that the oil takes 2 - 90s and I think a 180 before entering the block. If you leave the center one out it will go from your sandwich style oil thermostat, directly into the engine, and from what I have seen gives the motor a little better oil presure. Most people like to see the oil temp before the oil enters the cooler, or have tapped one into the side of the oil pan. Does your sandwitch adapter have a small open plug on the side for a temp/pressure gauge?

no,ive never ran into a problem before,just wondering if it was a gen vi only thing

from my understanding the outside valve has to be swapped or you are setting your self up for destruction.

28eliminator, I am not 100% sure, I will check it when I get home tonight. I really want a temp gauge on here so I need to figure out the best option

True the outside bypass valve needs to be the 30lb one. There is too much back pressure with the oil going to a remote filter then to a remote oil cooler. The valve will open and send unfiltered and uncooled oil to the motor. Many guys on this forum just plug the orific, forcing all the oil to the filter and cooler which solves the problem altogether.

the first 2 valves I ordered came, GM # 25013759 right on the box which I have also seem on this site listed as a 30#. I am not sure what is different between that one and the 25161284? are they both ok to use? doesn't matter on this motor since I have both now but I have a stroker motor I am putting together and would like to use one of them if it is ok

I put my sending units in the remote filter heads. I want to see what it is before it goes to the oil cooler. Also I just monitor it for any changes, if it starts running hotter than before there is a problem.

I do not have a remote filter on mine. I am wondering if I need to drill and tap my sandwich style oil thermostat. there is also a tap above the oil filter that the machine shop thought would be a good place. I think that there is normally a oil temp switch there for the stock buzzer dealy that I have never had hooked up. this would be very ideal for me as far as routing wires