Is it possible the valve starts to open at 12, but still allows pressure to climb to 20 or so? I thought the stock merc valve started to open at 20 and then fully opened at 30 which some builders think is too high. Like a radiator cap, it doesn't let all of the pressure out at once, but starts to hiss at a certain PSI and lets out more steam as the pressure increases until it reaches full open position.

I'm getting mixed reviews. The water pressure at WOT was 12 after the spring had been cut. Several have said that this is too low, while others have said that this shouldn't be concern. I don't want to have the head work in question, but don't want to run excessive pressure either.

You can always put a SS washer for a 3/4" bolt behind the spring to bump the pressure back up a bit if you wish.

WB. When I installed my valves last week, I left the dump hose long and hanging over the side to watch it work. Dry until 25psi. Then the dump volume increased as pressure did. The valve fluttered while controling the pressure by a few lbs. I suppose if the dump hose was just a little smaller, it would give just a bit of restriction on the back side of the relief valve to stabilize it a bit.

Should have mine Wed.

They have arrived...Orange stripe spring is out and which springs did you go with out of McMaster Carr?

They do. 302 SS.
Mine just came in. Look exactly like the original. Was afraid the number of coils might be different.

pt # 1986K18 $11.17 for 6

Thanks, Will call pick up in the morning.... I live 2min from them.

WOW! They are perfect replacements! Thanks for the direction on those.

Keep track of your free spring length and WOT pressure. Just for a comparison of what I end up with. That's my weekend project.

Your welcome

I'm thinking they are good to go right out of the bag....I will see Saturday.