Water pressure issues. Way too much
 

So what should the water pressure be on a 502 mag efi with KE headers? I built a new motor over the winter and I just got her going. Well I installed a water guage for the first time. I'm getting close to 5lbs at idle and If I bump it up to 1200rpm I get about 13psi of pressure without even moving the boat. I can actuall free rev it and get 22or23psi. Once I get on plane I'm running about 40psi, and today I ran her up to 5k and got 55psi (aprox 70mph)

Motor specs are as follows
Stock 502 mag bottom end
AFR 315 heads,
Crane 741,
Holley single plane Efi intake,
Keith Eickert headers,
Still runing the Circ pump.
Only thing I changed with the water is I added a Hardin 3"x19" oil cooler, a 2"x12" fuel cooler, changed the T-stat to a 140, and rebuilt the stock water pump with a merc kit. My drive has low water pickup and the regular pickup (bravo 1x)

Anyone got any guesses?

Frank

Frank
I was told that with the low water pickups and higher performance motors you need to install a pressure relief valve and vent the excess water either into the exhaust or out through the hull. We had to do this on my hp 500s this spring.
Don't ask me about specs or the specifics on how to hook it up. I'll be the first to admit that i have to hire mechanics to do that stuff for me. Hope this helps.
Jim

Assuming that the gauge is correct, there is an obstruction some where that is causing the water passage to be semi blocked,(sand, Thermostat not all the way open etc) which is increasing the pressure. The dual pickup drive does increase pressure, but not by that much. My single, low water pickup reads 12 lbs at 5800 RPM. nothing on the hose or ideling, and I have the same system as you, except I have a restrictor instead of teh thermostat.

Where is your gauge reading from?

I'm going to try removing the thermostat tomorrow and see what that does. I backflushed everything yesterday to see if there was some type of obstruction and everything flowed very free.

If the t-stat doesn't work I'm just going to run a 5/8" hose from my intake to my A/C through hull and dump some water overboard, just to see what that does.

I wan't to get this under control before I blow a gasket out. I have cometic head gaskets and felpro intakes.

Frank

Can you post a picture of your water system rigging? Did you change any exit water hoses? What exhaust system did the KE exhaust system replace? Are you measuring water pressure after all the new coolers? Is the WP measured at the intake manifold?
It sounds like maybe the KE exhaust may be restricting the water flow and raising the WP...need more info.

I have my water pressure gauge hooked up to the bottom of the block, and a 2nd guage (oil pressure) hooked to the intake. My water gauge only goes to 30 psi, that's why I added the other one.

Frank

I was thinking along those same lines. I'm wondering if the KE's, since they are so much taller and bigger than the merc manifold, are restricting the flow because I have to push all of that water up the header.

I'm measuring the water pressure both at the bottom of the block and at the intake manifold.

I didn't change any configuration of the stock merc water routing. The KE's have 1 water inlet at the bottom just like the stockers did.

Thanks,
Frank

im currently having the same problem. same drives as you. put duck tape over the LWP holes and reduced pressure from 30 psi at WOT to 20 psi at wot. going to install the relief valve kits. merc #863208A3

The gauge on the block could easiely have junk in it from the block. The intake one is the best place to mount it.

You could have a restriction in your exhaust, as was mentioned, but its not from having to push the water up hill. The stock system has to push a lot of water up hill from cool fuel to the Stat housing. (and from the pump to the back of the motor) BUT you could have some junk in the headers water passage.

A couple of days ago I took the hose off the top and bottom of the headers and ran water from the top down to see if I had any crap in there. They flowed as much water as I could throw at them. I never did try the tail pipes though. But I did backflush from the T-stat housing to the water pump and it was very free flowing.

Thanks,
Frank

Can you by-pass the tail pipes and put a temporary hose from KE manifold over the side? Just long enough to test the change in WP.
Another easy test is to run a dump hose from a water plug on the intake manifold to a temp hose overboard. We have a permanent bleed/dump hose from intakes to relieve air pockets and to bleed WP.

I'm going to give it a try today. I'm also going to try running without a T-stat to see what that does. I wonder if my Comtic head gaskets could have anything to do with it?

What size are your bleed off lines? Are they in the back of the intakes or up front?

THanks,
Frank

I would just use a 1/2" hose at this point to see what happens. If this ends up as the solution, I will get you all the info on a suggested permanent rigging.

Any plug will work for a test.

Ok, here's what I've done so far. I eliminated the tails (no difference) then I bypassed the water to the headers for a quick start (no difference). I changed out my brand new merc 140 t-stat with a high flow 140 t-stat (no difference).

So that means the problem is somewhere in the motor, or circ pump right? What should I do next? Just run the dump on there?

Thanks,
Frank

If I understand correctly, you have the water from the intake manifold thermostat housing (w/o thermostat) free flowing out dump hoses (by-passing the exhaust) and you are reading 20+ lbs WP at the intake manifold? Is this correct?

That is correct, except I do have a high flow T-stat installed. I haven't ran it without a stat yet. I need to keep it in there for the efi.

Thanks,
Frank

This might be a problem. Mercury used by-pass hoses to the headers (bleed off) with a pretty ugly thermo housing on many engines. How is your water getting past the thermostat when it is closed? If it is just with a few small holes in the thermostat, this might be causing your high WP. Maybe a quick test without the thermostat?

you said that you have 13psi at 1200 not moving the boat, so you should be able to pull the stat and do that even with the efi.

as you are getting that high pressure with no movement, it has to be a restriction from the impeller to the block. (out of the block seems okay based on the elimation of the headers in your one test) your water pickups have no real effect sitting still on pressure

you can put a dump line from the intake front or rear and see if that lowers it.

you can also make a cheap PCV tap to insert anywhere into the water lines. as your water exit is okay, thi sshould show you where on input the restriction/problem is.

you can also make a cheap tap from PCV pipe and insert it into the water lines any place that you like.

Here is a pic of my T-stat housing. I'll try no T-stat tomorrow, but I have a feeling I'm going to have to run a dump valve. Or at least a dump off the intake.

A few things I have picked up about the pressure issue, most head gaskets start to weep "externally" around 30psi. Quite a few feel 20psi should be the max in the system. The Merc valves are set for 30psi that leaves you on the edge. Dumping water into the exhaust increases back pressure hurts speed it should go over board, no matter who's valves you use it must have a strainer ahead of it or it will be useless in no time!. Want to check out a high quality adjustable valve check out http://straval.com/ I feel they are better quality and also less expensive then the Merc valve.

Phil

You do have the thermo housing with the hose dumps to the exhaust that by-pass the thermostat. I don't get why you have high WP at low RPM's/speed if you are measuring pressure at the intake with the hoses to the exhaust manifolds disconnected. If all the above is true, try an small rubber hose in an 1/8" NPT hose fitting in your intake to a mechanical WP gauge to check WP. You can also look for a restriction in one of your hoses. This will make sure you aren't chasing ghost.
For over 1 yr, we looked for an overheating problem in one of my Mercury engines. It turned our to be a defect from the factory in the Merc thermo housing (similar to yours). The restriction was from a 1/2" NPT red plastic thread protector that got pushed in vs removed when the foactory NPT fittings were installed. After a few yrs of bouncing around inside, it finally wedged in a passage, and we could not see it. After we finally pinned down down the is issue/location and replaced the housing. We then cut the old housing in half with a band saw and found the POS plastic...f_ _ _ me.
I am now drinking a beer to celerbrate this 15 yr old discovery...again! I understand your frustration.