I just put my 87 Formula 311 back in the water. Both motors were freshened up this year. Oil pressure on a mechanical gauge for both motors were perfect. Installed both motors in the boat and the port motor is reading about 10 psi less than the starboard motor. This was the case last time the boat was in the water as well. I had replaced the sending unit on the port motor with the typical sierra unit for mercruiser, and the sender I pulled out appeared to have been replaced previously. I am wondering if this is the correct sender for my VDO gauges. The 0-80 psi gauge specs call for a 10-180 ohm sending unit but I will be damned if I can find the proper specs for the sierra or mercruiser units. If anybody here can verify if I am using the correct sender or not I would greatly appreciate it. I ordered a NOS gauge off of fleaBay, but I am thinking I may need a sender to go along with it. Thanks in advance.

Matt, you need Napa Part # 701-1823. VDO senders and guages are often times backwards from the rest of the world. Good Luck Tyler

Looks like VDO offers 2 gauges in a 0-80psi Blue Line series. I suspect the ones in the boat are for the us 240-33 ohm senders, but the NOS gauge I just bought is setup for the 10-180 sender. I ordered the appropriate sender this morning for the new gauge and I will see if that cures what ails it. It is the OCD in me that drives me nuts having one engine reading lower oil pressure than the other even though I know they were both fine on the floor.