Codered

Mudball with all do respect to your post Please explain how removing a circ. pump increases water pressure .

Mudball

Here is an explanation from a fellow on the 'other' forum. It's the best verbal description I have seen of the stock system...

'Quote':
9) The sea water pump feeds water into the factory t-stat housing by means of the large inlet on the right. I takes a right turn to the back and then at the back it u-turns back up the left to the front. In the back there are a few holes to let some of this water raise up into the chamber that the water outlets to the exhaust are. This chamber is also where the t-stat (when open) feeds into. Yup, two chambers - well thought out I must say. Okay, back to the front - the cool water then enters the very large outlet that connects to the hose that goes to the recirculating pump. The rec. pump is a real pump, therefore it is drawing water from this area - the significance is that it is reducing pressure here since it is pulling, not pushing here. Remember, the t-stat housing also bleeds some water thru to the exhaust which is open to the atmosphere and thus water psi reduces here also. Ahhh, so this is why this system has lower psi than the others! Yes, sir. Smart engineering!

Whew! getting long? Yup! Not like I really like to type vs talk but many will read this, so let's go further.

The water get's pulled in thru the rec. pump and then get's pushed thru the block, heads, etc. So, what if the t-stat is closed ? Ahhh, the water slows down, almost stops, and farther back the water is going into the upper chamber of the t-stat housing and out the exhaust. Remember?

It's really an ingenious system.
'End quote'

Codered

Mudball you type well but let me ask you this if all this water pressure exist in the block why would steam pockets develop .All this water pressure should collapse steam pockets . Also if water pressure is such an issue ,Why doesnt REX or STAINLESS MARINE orEDDIE MARINE address it.

Mudball

Hi Codered:

First of all, let me say that I am NOT a guru on this subject! I just know what I have been through recently trying to get this crossover to work, and what others have also been through.
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When I ordered my EMI crossover, I specifically asked them about any problems. They said there were none. It even came with a thermostat with one little 1/8" hole in it.
To answer your question, I have no idea why those suppliers don't know about the thermostat/pressure problem, other than most crossovers are used in blower applications where they are the only option (no room for a circ pump). I don't know of any blower motors running thermostats. Many run the restrictor washers, though...These bump the water pressure.
With nothing in there, the water pressure is very low. I never saw much over 10psi at WOT with nothing in there.
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I also don't know about any steam pocket problems. I don't believe that at least I have that problem. After a romp, my head temps are close to each other and vary little from front to back.
My Merc relief valve limits pressure to 25psi.
Kent

Mudball

I might add, it is interesting to see the relief valve open! When the thermostat is closed, it shoots (more like pulses) water about six+ feet out the side of the boat!! It looks like a SUPER bilge pump working!! When the thermostat is open, it stills lets water out, but not nearly as much.
Kent

Codered

Mudball I appreciate your time and insight on the crossover situation.I still see much confusion and mis -information by the manufacturers on this subject

zahndok

Merc runs a thermostat on their 575sci blower motor. I don't know if Merc runs them on their bigger blower motors. When the water is cold in the winter I avoid WOT on my 575 because of high water pressure in the 30-35 range. If I ever change the thermostat I think I'll drill some holes in it to see if that helps.

US1 Fountain

The holes drilles in the t-stats are not for pressure relief, they are to bleed the air out of the motor while the stat is closed. Just think, how much water can you shoot thru a hole smaller than a straw?

Been there done that. Never go back. Like Mudball stated, the best way is a separate pressure relief valve before the crossover.

mcollinstn

zahndok, your t-stat already has a little hole in it.

The marine t-stats have the hole to bleed air out.
Steam pockets form if you aren't running the correct headgaskets and/or a marine stat (or holes drilled in a non marine stat). Basically trapped air. Block pressure collapse steam pockets? Well, yes and no. If you are at a hot spot, your hot pocket of air can "breed" more air out of the water. Have you never heard of a steam engine? They ran on steam at 150 to 200 psi. Block pressure should never go over 20 or so. Not enough to collapse all steam pockets in some applications. If you can give the trapped air a place to go, then the resultant water that replaces it will cool the hot spot and the steam pocket is gone. Take a look at some drag intakes. Little pipe threaded ports over the rear water passages. That's for a steam line that you run to the main water crossover in the intake.

vette131

guys i removed a recirculating pump from my 502 & experienced dramatic shifts in temperature with a stock thermostat. after doing some research i drilled a couple small holes in the thermostat & my problem vanished. my engine now ran at 140-150 all the time after warm up. a recirculation pump won't suck water past a failed raw water
pump. you need a water pressure gauge regardless whether you runa recirc pump or not. the holes in a thermostat with a crossover system allow the system to maintain a constant temp, without the dramatic temerature swings you would get without the holes. crossovers work great & eliminate an automotive component that is prone to failure. i didn't see any real gain in speed with a crossover but i was very happy with the reliability & simplicity of the modification.