What are the port/line sizes on the Merc 500efi thermostat adapter housing? I want to adapt this to my mpi motors. Are oil lines for the mpi the same size as the HPefi lines (diameter & flow)?Thanks in Adavance. Dave

unless its dry sumped, -10 lines are fine. youll get 25 responses here that will spec -12 and even -16 but he flow rate of even the hi flow pumps will call for -10. larger lines aren't going to hurt anything... just take up room and cost more.

std on a 502 mag mpi is actually closer to -8.

Thanks Steve. Are the HP500 lines the same size as the 502mag lines? Wouldn't I be limited by the port size on the T-stat housing? Take Care, Dave

i can't say. smitty did a very comprehensive post here that dealt with this subject. very detailed and well researched and , in my opinion , essentially correct in all his conclusions. its worth finding and reading. beyond that, and one of the points he stresses, is that you have to look at the id of the fittings ( which leads to my point) if the id of the firtting is .375
then lines w/ .5 are going to be fine. he suggests tha a lot of the fittings are smaller than .375 and he is correct im sure. that is scary to a lot of people but i always figured that the factory was smarter than i was and wouldn't have made 200,000 of them that way if there was a problem... but thats just me. read smittys post and do what he says and you can't go wrong.

I just put the HP500EFI oil thermostats on my motors this summer. I used -10 hose and fittings, and put all new oil lines on it. I used Parker hose & fittings. One thing I found out is if you use Parker hose you want to make sure you buy the high temp hose. Their standard hose temp didn't go as high as you would think. Using the -10 hose it turned out very nice, and is working out great.

Thanks for the replies. 10AN it is. ONE MORE QUESTION...: 1/2" npt to 10AN is compatible as far as the 1/2" npt part of the adapter not being more of a restriction than the 10AN side,right?? Thanks Again, Dave

Dave,

That is the way I did mine. I used the 1/2" pipe 90's to -10 push lock fittings.
It worked out well.