540 heating up with stat installed
 

:mad: 540 CI carbed with a cross over. Without a stat, temp doesnt come up. I put a 140 stat with 2 small holes drilled in it, temp comes up to 180 to 200. Gauge worked fine last year with other motor..?? Put stat in to bring up water temp alittle. Getting some condensation in breathers. Figured it was better for engine with alittle heat. Engine dynoed with 140 degree water temp, so I should run it like that? Oil temp runs at about 140 - 160 when im under way, comes back down at idle. Why is water temp going up so high? Also bought another new stat, went to same temp, so stat is not the problem.????????????? Is it ok to run boat w/o stat? Everyone has a different opinion on this matter. Do I lose power running engine cool, or gain power? :food-smiley-009:

Any feedback ?:party-smiley-004:

Does the crossover have a bypass?

i could be wrong but it seems to me that crossover motors are supposed to run blanking plates... not tstats. my suggestion would be to get an old tstat and punch the center out of it and try that and adjust that hole size until it does what you want.

The crossover does have a bypass.....................

The hole in the stat sounds like a possibility. How big of a hole should I start with?

I am having the same issue. I have a 142 stat with 3 3/16 holes in it. Crossover with bypass. Mine goes to 200. Prior motor with same set up went to 190 on Gaffrig guage, but on the prior Faria guage it was 160. I still have the Faria guage and I am going to see what it says.

The oil temps of 140-160 are way too low. You need to see at least 212* on a regular basis to burn off any condensation.

The water temps should be fairly stable around 150* with a 140 Tstat. I would drill 2 more holes at least and probably make them all bigger. It will work more like a restrictor plate then.

It really makes no sense that water temps are too high and oil temps are too low.

i may have not made my self clear. w/ a crossover motor i don't think you want an operating tstat at all. i am suggesting a flat plate with a 1" hole in it in PLACE of the stat. an easy way to accomplish that is to knock th center operating mechanism completely out of a stat... thats just an easy way to accomplish the same thing. it is NEVER a good idea to drill holes in a stat in an attempt to change its calibration or act as a by pass.

Off subject a little but what are the advantages of a bypass setup?

Hi griff-

Well, I dont understand why the water temp is going so high with a 140 stat ? With a crossover. Ive tried 2 different stats to eliminate a possible bad stat. If I can get the water temp to 140-150 consistently,the oil temp should come up also . Right?
Im going to get one of those heat sensing laser guns today to be sure that the water temp is at the temp that my gauge says its at. Im getting mixed reviews about hollowing out the stat, but willing to give it a try.

Please let me know what you come up with!

On this same subject
 

I am in the process of changing my theromstats on 500 hp's, efi. Mercury stock thermostat call for the 140 degree thermostat. Is it better to run the 160 degree thermostat instead of the 140?

Im going to lazer test the water temp first, then hollow out a stat and go from there..Thank you

Have you tried replacing the sea pump impeller?

Steve, I have a 160 deg thermostat with (2) 1/8" holes and it works perfect. At hot idle it runs 170 and on plane 150. I do have a bypass hose. I think the ones without a bypass hose need the plate you are talking about.

Yes , the impeller is new.

The EFI motors are supposed to have 160 deg. thermostats. The computer will think the motor is still cold with anything less and tend to run rich. A cross over with a bypass is meant to run with a thermostat Mine runs rock solid at 120 degrees with a 120 degree therm. and 2 1/8 holes drilled in it. My bypass uses a 3/4' hose, how large is yours? Oil temp lower than water temp doesn't make a lot of sense. I would double check the gauge. If it checks, then the problem is likely related to water flow. Check all of the usual things, impellor, hoses, make sure nothing is plugged etc.

Oil temp. does seem low. I have a 540 also with a 140 t-stat. I do run a circulation pump on the motor. Temps. always stay at 140 on the water. I also use a t-stat on my oil cooler .The oil runs from 215-235. What type of water pickup do you have?

Its funny you mention the bypass hose size. I was looking at it thinking it looked small. I need to check the size. Possibly a problem if too small?

Also should make sure the drilled bypass holes are at least 1/8 " in size too?

Holy sh#t, I just remembered something else. Water pressure. At an idle , its at 5 lbs, but goes up rapidly as rpms come up. Like 10 lbs every 1000 rpm. So at 3500 prm, there is 35lbs water pressure. My gauge only goes to 35 or 40 lbs so I dont know what happens after that. If I take the stat out, its always between 5 and 15 lbs of water pressure. The water pressure censor is in the top of the intake manifold next to the thermostat. Could this high pressure be effecting the temp?

Yes. Some people have a problem with crossovers and high water pressure. It can lead to blown intake and head gaskets and water in your engine. Serious problem!!! I've never had that problen but the bypass on my crossovers is pretty big. You can get a pressure relief valve but that won't help your water temps any and may make it worse. Maybe it's the design of your crossover doesn't work well with a thermostat. If your set up works well with out a thermostat, you could just install an oil thermostat to keep oil temps up and leave the water therm. out. Could you post a picture of your set up?

if this thing has a full cross over, it doesn't have a traditional water pump, right ? if it doesn't have a traditional water pump, then it is going to need a blanking sleeve with a big hole or he is going to see the big pressures he is seeing. i admit that i could be completely wrong here because a lot of people do a lot of , what i consider to be weird things, but for me there are only two systems... the ones with the full crossover and no water pump and a blanking plate sized to control the water flow to achieve the thermal balance you need, or the non crossovr ones that do have a water pump and , as such the correct bypass and THOSE need a conventional unmodified thermostat.

everything else is something else. if understand this particular configuration correctly, it has a full crossover and no water pump. for me, that answer is simple... a blanking plate w/ a 1" hole more or less. its not efi so temp whileimportant for all the usual reason is not critical to function...

Stevexm, they do make crossovers for use with a thermostat. They have a bypass to allow water to the exhaust manifolds when the thermostat is closed. Don't try to run a termostat with a crossover without a bypass! With out the bypass you would cook your exhaust. You also need the proper matching thermostat housing. It has connections for 3 hoses, 1 for each exhaust manifold and 1 for the hose to the crossover. Take a look at the Stainless Marine or CP Performance catalog online.

so what configuration does this guy actually have ? seems to me that if its one of the two i mentioned or the one you identify , then the answer should be self evident... there really is no mixum and matchum ... each configuration demands its own cut and dried answer...

and if his system has a true bypass then he shouldn't be seeing the pressure spikes...

Steve- I have a "true" crossover system. Including a bypass hose. Have a sea pump and no circulator pump twith a stat and 2 small holes drilled in it.

Sounds like what I use. Mine works perfect. Can you take a picture? Maybe we could see somthing?

he's right. with that confuration you should'n see hi water pressure and the system should work ( with the exception of the holes in the tstat which could easily screw things up but who knows ) is it possible that this thing has lost a head gasket into a water gallery which is both causing the pressure and the wild temp fluctuations ? the cooling arrangement seems pretty straight forward and i would expect it to work... logic suggests you may be looking in the wrong place...

steve- I dont know man. The oil in the pan is fine , not milky. Engine runs great, idles great, no fouled plugs...........I need to do some testing and by process of elimination, make sure I not getting any false readings on my gauges. I really appreciate your input. I will keep you up to date....Kevin

why not just take the t-stats out? especially if its a carb motor... what temps does it run without them?

I have had the stat out.(single engine). But am getting alittle condensation in the breathers. Thought giving some water temp might help. Plus, everyone telling me not to run engine cold. Water temp doesnt move with no stat. Oil temp goes up to 140-160 when I beat it up. But then goes back down to 120. Just thought it would be better for engine running it with alittle heat in it.

Actually the 500EFI's use a 140* Tstat. I thought they used a 160 too until somebody said differently and I double checked on www.mercruiserparts.com

Thanks for the info. It must be just the black motors that use the 160.

I would like to see a picture of the plumbing also. Some thermostat housings are not designed to be used with a crossover. Water from the by pass interferes with the temp sensing part of the thermostat preventing it from opening. A picture could give us a clue.

When I ordered the crossover, It actually came with a braided bypass line and a 140 stat with a 1/8 hole drilled in the outer flat of the stat .Thats how it came in the crossover kit.

Was the thermostat housing part of the kit?

Yes

i may have missed this in the beginning but let me ask this... has the motor EVER maintained the correct STABLE temperature with the crossover kit as installed from new ? in short... has it EVER worked and is this something new or has it NEVER worked as delivered ?

My motors are proof that crossovers and thermostats work. I also know of many others with similar systems. The problem must be elsewhere. You said water pressure is too high. I'm assuming that's with the thermostat open because you say it's maxing the gauge at 3500 rpm. The gauge sender is at the intake manifold so the only restriction left after that are the exhaust manifolds. Have you checked the exhaust's for corrosion or other blockages? Did you ever get around to checking the gauge?

Well, I had it on a different engine last year, but without a thermostat and no bypass hose. Now, with a bigger, and alot more expensive engine, Im trying to help it last and perform well as long as possible. So, I did use the crossover but without a stat. Put the stat in this year w/ a bypass line, the water pressure shoots up and the 140 stat goes to 180 to 200.