after installing that thermastat id be watching youre water pressure .. it will jump up fast at higher speeds .. probly will need water relief and water dump .. i spiked to 40 psi in a new york second , just saying .. more too it than just adding a stat .. im no expert though ..

Yes water pressure gauges going in as I stated in another post, might have missed it but yes I will be using gauges

Good move Tim, water pressure is extremely important.

I will share my experience with by-pass crossovers. The best water crossover is the one from Stainless Marine, the thermostat housing is cast polished stainless, that has a diverter in which keeps the cold water from confusing the thermostat with cold water. That cold water will, make the thermostat close early NOT ALLOWING, the water to flow the hot water from the last 2 cylinders on each bank. You will never see a high temp reading on the gauge, allowing the rear cylinders to overheat, causing the cylinder head to expand beyond the quench of the gasket.
I experienced; a confused thermostat on a 750 hp 540 NA I was told drill 5-7 holes in thermostat. This issue cost me much time and $$$$, the end result of the cold water hitting the top of the thermostat, wasn't a enjoyable journey, for my clients lost boating time and my time and money to correct the issue. the end result was a dropped valve seat and a bent valve. After repairs were made, a thermo-heat gun determined, 300 + degrees in back cylinders. determining what was going on. The only bypass I us now if needed is from Jerry @ Stainless Marine.

By far the best one out there!

Good info, where does one find this specific thermostat housing with the diverter? Stainless Marine's site isnt working. Is there a part # on it?

I think CP PERFORMANCE sells them part# 520-sm 295w.

Mine are stainless marine but old system, I will try donlol around later when I am on computer...

Is that good stuff ?

I'm glad to here you are not on fukitol:
http://3.bp.blogspot.com/-LCAKPEm55b...00/fukitol.jpg

I have not read all the posts but would this help whomever

https://www.cpperformance.com/Instru...540-160200.pdf

and or

http://www.cpperformance.com/p-12564...t-divider.aspx

Lol typo !!

Found a pic of the internal water 'divider'

http://www.cpperformance.com/images/...e/12564_2_.jpg

Yes I tried to land it on that pic ^^^^ but when I posted it the whole housing only showed. There is 3 images from the link I posted. I am not that smart when it comes to doing all this internet stuff. Just saying

Still have a ton of old school in me

I have the harden marine like was posted above.

Are you guys saying the internal diverter is adequate? I just looked at mine and it's the same as the one SB just posted.

I hate crossovers. LOL. Temp fighting / psi fighting / uuurggghhh.

I think this thread is also really bringing in the importance of either using water dumps off the rear coolant holes in the intake - hopefully everyone using crossovers have them (rear coolant ports in intake) - or atleast using lines to bring water from there to thermostat housing.

I use the recirc system but I still run those lines.

http://www.dragstuff.com/forum/viewtopic.php?f=2&t=3612

Pic 1 is what I was going to say also. cooling hose from front of intake to back.

I have stainless steel lines that run either side of the intake between the rear and front water jackets. In this pic, the hard lines on the sides:
http://i205.photobucket.com/albums/b...psldt7nilx.jpg
From the side:
http://i205.photobucket.com/albums/b...psoxweoj73.jpg

here is some of these guys set up for cooling - check out the extra water circ pump hoses leading back into the mid head area and of course front to rear intake cooling hoses.

http://www.enginebuildermag.com/wp-c...0000048552.jpg

as a side note .. when paul pfaff put my pakages together .. fully rigged ready to drop . i talked about water temp .. and i was told as long as youre running a oil stat system witch brings oil temps to operating range there is no need ? was he correct . they are a big builder of high end motors in southern cal ... told him i boat in cooler waters than them

That's fine.I have ran into that too. Southern builder sends motor up here. Engine has cooling issues. They get perplexed. In the middle of summer warmer water they work fine.

Not everyone can possibly know everything.

When you are a manufacturer, you have to test in all conditions.

If clearances are "loose" all around as MOST marine engines are it will not be issue..

True...but getting oil temp up is killer tough incold water. Even with t-stats. 5 million hrs after cruising for a bit,you get good oil temp. Then you come off plane to take a break. Your oil temps plummet back to cold.Now you want to take off again,but noooooooooo...you gotta wait for another 5million hrs.

If you don't let the temps get up your oil gets 'soggy'.

Again, this is for some of us that boat, at times. in very cold water. But, some people around here only boat end of June thru August, so,they are all set.

=================================================

I here timeandtime again around here,even you today or yesterday, I don't care if I lose 10-15hp or not make an extra 10-15hp.

Well, the recirc pump doesn'ttake that much power to spin under 6k, so why do many people spend $$$ on cross overs that don't need them.

It's like the guy who buys a $300 cast steel crank instead of a $700 forged crank, but has $300 valve covers and sends them out to a custom painter.

FF - not singling you out cause you already had these.

Just making a point with what I see in this performanceboat worldand trying to makesomesense. LOL.

My space bar is not workingto well. LOL.

I know some people who got rid of their circ pump and went with a crossover because it "cleans up" the front of the engine and looks nicer. You have to have that bling under the hatch, ya know! ;)

my engines build oil temp fairly fast .. 5 minutes maybe .. i also run teague offshore coolers ,, bounce up to 3 k, let em warm up, loosen up, n then its go time .. i can wait 5 minutes just listning to that cam thump pretty noises to my ears .. besides people on shore love to hear them too .. lol nothing like big cammed idling big blocks ....

Put stats 140 stats in, ran on the hose and they will not open, up to 180 and still not open..the bypass hose is dumping cold water on stat keeping it from opening... my stainless marine housings do not have that diverter in there to stop that....

I now have loose clearances in lifter bores and guides, might just run the way its been for years.....

I just got engines in and running good Sunday, no time to hunt down and install circ pumps....I did order water restrictors may play with that now that I wave water pressure gauges installed...

You do atleast have some holes dilled in the oute edge of the tstat's right ? And a way to gauge water psi ?

You must have one heck of a water main to be able to test that on the hose. I never could. Heck I tried using a 30 gallon tub and letting the hose run in the tub and couldn't run it more than a minute or so.

I drilled 2 1/8" holes in stats but I removed them since they refused to open..

I never had any issues running on hose here, plenty of flow...

Back some years, my dyno testing side lined into t-stat and cossover testing. We had 200+ gallon supply with a garden hose dumping into those taanks to buy us more time.

I learned very f'ing quickly how much damn water those bravo belt driven pumps can move. Amazing !

its one or the other,,you cant run the bypass and expect the thermostat to open...we told you time after time you have to use the phuckin bypass thermostats..NOT the car ones you drill holes in....you got a text..

Is the type you're talking about FIXX? http://www.ebay.com/itm/EMP-Stewart-...-/191416902341

Mike Fixx calm down I am trying to do what I can I didn't buy a car stat, I also show on all instructions to run he bypass hose with the stat..

Fuk this I'm done I will do whatever and not post anymore about learning.

If I took every persons idea that I was told I would be changing it daily and never boating at all....

The bypasses that I have were on my engines and others before I owned the boat for 20 years.... Engines clearances are opened up now so it should not even be issue at all, I was just looking at adding some heat.



I might be stupid but I cannot see how a CLOSED stat with NO bypass hose will flow enough to my exhaust through a couple small holes and ANY STAT if that was the case there would not even be a place for te BYPASS hose at all...

A buddy of mine is running west marine stats with 2 1/8" holes drilled and uses a bypass hose I gotta see how his works and mine don't...

Are they upside down?..... (ha, just kidding buddy).

FF - keep posting here. I'm curious.

I ran around the other day with stats and a bypass.

On one motor I got all the way up to 180 with a 140 stat in it with only 2 3/16 holes drilled in it. My current hypothesis is that the bypass was just keeping the stat fluttering. I am going to drill a 3rd hole next time out and see if I get enough flow to keep the backside from being over "cooled" by the bypass.

Contrary to what you had, I couldn't get any heat in it at idle on the hose....

So I have been following this thread with great interest as I am chasing stable engine temp as well.

I have a N/A 540 (680 HP) running a cross-over with bypass, T-stat and transom mounted pick-up. When I got the boat, it was running hotter than I liked (180-190) especially if run hard and then brought back down. I pulled the t-stat and it was a 160 deg with acouple of 3/16" diameter holes in it. Water pressure was just showing on the gage at idle (2-3 psi) and about 12-15 psi at speed. I replaced the T-stat with a Stewart High Flow 140 degree which had a small bypass hole in it. Temp came down to about 150 while running hard but sky-rocketed (to over 190) when coming back down. Water pressure over 70 MPH was too high as well (saw 30+ PSI and backed off).

That was it for the season and she went away for the winter with the thought I was going to add a Merc HP pressure relief valve since I have one on the shelf this spring. That will address the water pressure but not the wide temp swings.

I'm a believer in the "confused T-Stat" theory as the bypass water (my t-stat housing has no deflector) is surely dumping onto the t-stat especially when there is less water flow. This would explain the spike in temp when backing down after a hard run.

Over the winter I spec'd out a low pressure high flow, in-line pressure relief valve (3/4") that I plan to put into the bypass line between the crossover and t-stat housing. The valve is SST with an adjustable cracking pressure which I have a starting setting of 3.5 PSI. Also a really nice piece that is compact enough to thread into the 3/4 NPT port of the crossover and take the existing hose barb by shortening the bypass hose a couple of inches. Theory is that if the T-stat is open, there will be at least 3.5 PSI higher pressure feeding the block than the bypass/exhaust, helping to keep the hot cooling water on the sensing side of the T-stat. This is similar to the restrictor plug stuffed into the bypass hose I saw in a previous post only a little more positive in forcing the flow through the block.

Of course, then I saw the T-stat housings with the deflector or better yet, the Harding Marine one that isolates the cold water from the T-stat. Either way, I can't help but think that creating some backpressure in the bypass line will always ensure preferential and adequate flow to the motor regardless of flow rate as well as to keep the sensing element of the T-stat flushed with the water coming from the block and heads vs the raw water pump.

Anyway, haven't even splashed the boat yet this year but will be testing come the beginning of July. Will post with my findinsgs.

Sorry for being long winded but thanks to the OP and all the other contributors as this thread has filled in a number of blanks for me!

Cheers,

I bought a 38 scarab with 500hp and crossovers with bypass hoses in Cali. On the way home to Missouri we stopped at lake Havasu for two days a water tested the boat. After watching the temp gages cycle from 145 to 220 plus I quickly removed the car thermostats and drilled 4 1/4in holes in each. No more cycling but no heat in the engines. After returning home I bought Merc Racing high flow 140 Tstats drilled 2 1/8 holes and still had high temp cycling issues. Pulled them out and drill 2 more for a total of 4 1/8 holes per stat. Now it idles at 145 running hard 165 maybe 170max Holes are dilled as evenly spaced as possable on the center upright cone of the T-stat. Two seasons and going on the third with no problems.Checked heads with heat gun and no indication of hot spots. It was amazing the difference two more holes made. Start with two or three and sneak up on it. Good luck