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