Crossover vs stock circulating pump
 

I have a Mercury HP 500 carb engine, all new set up back to factory specs with the exception of a better spring set. I installed a new crossover and thermostat housing in place of my original Mercury circulating pump with a 160 degrees thermostat, I am noticing hotter temps ranging from 200 to 225 even at almost any speed and steamy exhaust. I live in Gulf Shores Alabama and our water temps haven't gotten really cold yet, should I re-install the circulating pump rather than use the crossover on this engine?
Please email me with responses, thanks:

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Did you drill holes in the thermostat? I have been using one for several years and has worked well, I have also found that the high flow thermostats work a better.

Yes I drilling 4 small holes around the outer perimeter of the thermostat itself, then re-installed it. Engine heated up fairly quickly to 200 degrees again. Not much water flowing through exhaust tubes either. I had hoped this set up would work fine, I like it so much better than having to have that circulation pump installed, but at the same time want the engine to run cooler.
I am wondering if I should try it without any thermostat before taking everything back off?

Also, does anyone happen to know the exact timing setting on the Merc 500 carb engine? I have been told it was 8 degrees but want to be sure. Thanks to all whom respond.

dont run the thermostat!, i could be wrong but i have the crossover with hp500 carb. its gonna run really cool hell i live on the same water as you do and on a hot day my temp wont hardly get over 150deg! dont just take my word for it get on the do it your self page and make sure, ive had this set up for 3yrs and i dont run thermostats!

Thanks, I plan to keep the set up if I can, no reason for it not to work. I plan to check for some restrictions at the transom and check the impeller, which was good before. One way or the other, I am going to cover this issue! My wife used to have a 89 Cafe Racer! Nice boats.

You nead to make sure your oil Temp. Is getting up to 212 or you will have condensation in your oil. And your water psi stays under 20 psi.

Do you have a by-pass so exhaust gets water when the thermostat is closed? If you don't you can't use a stat. They also make restrictor plates that help slow down water flow and build a little heat. Also your oil doesn't have to get over 212 degrees. 190-200 is fine.

got a pic of your setup? I would consider going back to the circ pump though..... more consistant temps ...and water Pressure ....you really gain nothing ....m

I would check your water pressure. With a good high flow stat you shouldn't be that hot. If you don't have a bypass, get one. I run in colder water, but even with a 650hp 524, I barely hit 150 with a 160 thermostat. My biggest problem with my system is the right side runs 15 degrees cooler than the left.

Loose the thermostats !

like mentioned..has to have a by pass with the stat, also use a merc 140 with about 4 1/8 holes drilled in it..ran the exact setup..ran 150 all the time...

You have something else going on.

For starters, I would not run the engines hard at 225* water temp. Thats pretty darn hot for a marine big block under tremendous load in a boat. Your oil temps must be very hot also if your water temps are that high.

You need a bypass hose, running from the crossover, to the thermostat housing. If you do not have this, you cannot run a thermostat. If you do have this, and the engine is still getting that hot, I would start looking for things like a lack of water flow. Such things as a clogged sea strainer, bad impeller, clogged oil cooler, collapsed hose, corroded water inlet at the transom if its a bravo, etc.

The reason your exhaust is probably steaming is its getting really hot, and the small amount of cold water they are getting is cooking in the manifolds and tails. I'd find the problem before you melt something.

There are a lot of myths about crossovers. Mine works perfect, to use a thermostat you must have the bypass hose. I used to use a standard thermostat and drilled two holes near the edge. I have more consistant temps now than with a water circulator. It also works better with a big oil cooler. This year I went with a high flow thermostat and drilled two holes in the center (looks like a cone) and they are even better now. I use a 160 degree thermostat and it runs about 160 deg at idle and about 150 running on plane. Good luck setting yours up, if you can post a pic or a link to one that would help.

x2

Thanks to everyone for your responses and help with the heating problem. My Crossover has the intake side naturally and one hose leading directly up to the matching thermostat housing. Then there are two other larger ports, one for each exhaust manifold. I was using a 160 degree thermostat with 4 small holes drilled into the outer parameters of the stat itself, this did not seem to change anything. I noticed yesterday that the water when on the Mercury pin flushette I have always used and works fine, that the water sort of surges, it'll pick up and then fall off, like a pump that looses it's prime. Therefore I am pulling the impeller today and checking everything for restrictions and impeller damage. I will post what I find later today.

Make sure u have the right thermostat gasket as well , if it has the square tip on the end your blocking water going to your risers

Problem solved!! after carefully checking everything, and replacing the impeller again, I found the cause, unbelievable but glad I found it. Restriction inside the oil cooler, some particles of plastic "not impeller material" got logged up and inside blocking the water flow. Cleaned it all out good and made damn sure it was clean, re-installed everything and now my good old 500 is running nice and very cool. About 120 degrees if that! Thanks to everyone whom responded and helped.

Glad you found the problem. Just noticed you are from Gulf Shores, went there last winter. Looked like a fun place to boat with the innercoastal waterway.