I still say the first thing you need to do is get accurate water pressure readings.

Have examined the T stat housing throughly?? Maybe the bypass system is bypassing water directly out the exhaust that should be going into the engine??

Had the tstat housing off yesterday, all good. Have not taken the crossover tube off but have gaskets arriving Monday. I did have the j-tube btwn crossover and circ pump off and didn’t see any corrosion in either direction.

I’ll need a lower range pressure gauge, like 0-5 psi. Couldn’t find one on the shelf anywhere. I don’t think the rubber hoses to pressure gauge are an issue in measuring because I use the same setup to measure pressure on our house.

I’m thinking there so little resistance to water flow that it doesn’t build pressure.

A 0-35 psi is just fine. That is standard for boat water pressure gauges. It is your set up of how you have them connected. The one on the riser is worthless as there is no resistance to create any pressure.

Went to the lake with no thermostat. Bought the wrong size clear hose for head gasket test. Will get proper size and retest next week. Still overheated at WOT but took a little longer. Gonna fill block and heads the evapo-rust for a couple days and flush.

There may be some risk with that. Large scales of oxidation can come off and cause issues.

If you choose to gonthat route...don't waste your money on Evaporust.

Water. 1L
CItric acid. 100g. (Powdered)
baking soda. 63g
Small amount of dish soap. (Surfactant)

Add water to tub. Add citric acid. Stir to mix. Add baking soda....stir it up...let it churn up. When done...add the small amount of dishsoap.

Works far better and longer than Evaporust.

But if you have scale blocking water from contacting block surface, I think you wpuld require a more mechanical cleaning and scraping if it's gone that far.

Griff is correct, if you don't have measurable water pressure feed to your engine circ pump, you don't have enough flow. If you don't have any water pressure in the block while running, the water will remove less heat from the contacted metal. Low or no pressure also allows hot pockets of steam to develop in block and heads.

have you looked at your hull?and thru hulls in line w/ the pick up

Have thought about pulling your injectors and having them flow tested? A lean condition could have you scratching your head on cooling. I also question this cause you had a melted piston at one point. Also, has the timing been checked? Might be worth having your tune looked at to see were the timing and fuel tables are. Message Arcticfriends aka Smitty on here as he does injectors and could view your tune.

I’ve been trying to figure out how to make some kind of adapter for a water pressure gauge to install inline immediately post raw pump but haven’t come up with anything.

The rust removal is just a shot in the dark. There’s really no visible scale in block ports or manifolds/risers. I thought about 30% vinegar but didn’t know what it would do to the circ pump seal. I’ve used it on a bulk diesel tank and it worked great. Evaporust might be a little safer as they say it wont hurt the seal on circ pump. I’ve decided to run a water head measurement again then change the impeller and run it again. Still plan on installing clear vinyl tubing to check for suction leaks and head gasket leaks.

i had injectors cleaned with new pintles and caps. One was replaced. Spark plugs are evenly carboned up, not lean.

it had a broken piston ring prior to rebuild.

fuel and timing curves are OEM.