Question about closed cooling systems

[Trap Jaw]

So, I just got the new boat fired up. It has an old 3.7L Mercruiser I/O. While running it I went back to check if there were any leaks on the new exahust manifold we installed and I put my hand on it. Wow, it was hot. Not hot like I burnt my hand but still hot enough that I couldn't leave it on there very long. The only I/O's I've seen have the raw water cooling systems and I thought they kept the manifold fairly cool. This is the first closed cooling system I've run across. If this is normal, so be it, it's not like I'm going to sit my fat butt on it while fishing. If not I want to get to diagnosing the problem quick, fishin season's a wasting.

[Diversion]

I have closed cooling on my boat, and my engine does run hotter than a raw water cooled engine. Not sure if my manifolds get as hot as what you are describing, but they are certainly warmer to the touch than those on a raw water cooler engine. What condition is your antifreeze in?

[rolmops]

Don't worry,it runs hotter because of the thermostat.As long as you can keep your hand on it for a reasonable time you are fine.

In fact when you run a bit hotter you will have better fuel economy.

[ray koziatek]

I ant no expert but have talked to 1 or 2 ....did ya think to check your temp guage ?? ive rebuild a few motors over the years and you really need to pay attention that your thermostate is working proper (guage is your best tool on boat)..Too cold and ya can get condensation ,uneaven metal temps in cyc walls(rapid or accelarted wear) ,metal fatigue(failur and cracks),,,to hot and the thin walls between cyc can overheat,excessive valve wear (hot exhaust valve) warpage ,and a ton of other issues that can find a imperfection in yer motor.....and not usually at the dock,,,,so to you and others pay attention to your temp guage at speed,and trollin and more than once during the day....make a habbit of the driver to examine all guages ive had alt.wires vib and break,a plastic bag or weeds could cost you a new 3000.00 engine or more...But to answer you manifold touching issue ??????????????????????I ant gotta clue as i have a open system and some areas of the manifold are warmer than others ....maybe hank or 350 will chime in ....get to know as much as you can about your boat IE: if your thermostate is a 120 deg it shouldnt matter if your in 40 deg water or 70 deg water your guage should be very close to 120

[Trap Jaw]

Thanks guys. First of all, 90% of the antifreeze is new, had to change the exaust manifold and in moving hoses out of the way most was drained. What was left still looked good, well at least it wasn't discolored, but the guy we bought it off had some work done on the manifold two years ago. I may have overstated, no it isn't so hot I can't touch it. Like I said, I'm used to open cooling systems and was shocked how hot it was. Yes, I can hold my hand on it for quite some time. Temp. guage was reading 120, although that will probably be getting replaced since other guages are questionable. Thanks for putting me at ease. I just have zero experience with this system.

[Big Dave]

Works good for warming up your lunch on a cold day. These motors have an interesting charging system with a water cooled reg.

[tree top flyer]

I have a 3.7 and off the top of my head i think the therm opens at 140 or 160. If i knew what i was buying at the time i would never had bought a boat with that engine, but so be it. The way i understand it, merc mated the head of a big block ford onto there core. the problem is, everything is merc parts, making things 3 times expensive. if you look up engine rebuilds on line its about the most expensive u can have.Having a stater instead of a alternator makes things interesting also. there are interesting problems with the earlier models, iboats forum has also ben a big help with issues. The good side, (witch i bought it for) doesnt burn any gas trolling all day but can push my 20ft boat 50mph on the gps. good luck, i feel for ya

[motoman]

I have a 3.7 and off the top of my head i think the therm opens at 140 or 160. If i knew what i was buying at the time i would never had bought a boat with that engine, but so be it. The way i understand it, merc mated the head of a big block ford onto there core. the problem is, everything is merc parts, making things 3 times expensive. if you look up engine rebuilds on line its about the most expensive u can have.Having a stater instead of a alternator makes things interesting also. there are interesting problems with the earlier models, iboats forum has also ben a big help with issues. The good side, (witch i bought it for) doesnt burn any gas trolling all day but can push my 20ft boat 50mph on the gps. good luck, i feel for ya

when that $700 stator quits on ya put a single wire alternator on it for $75 bucks is what i did !

[Jolly II]

That's a good idea Motoman! I think there are even conversion kits out there to put a alternater on it to replace the stator.

I've got the same engine in my sportcraft. I always check the antifreeze and oil levels before starting in the morning. I do have a jug of each up front to keep the fluids topped off. The second thing, as Ray K stated, when I'm running the engine I watch my temp gage as much as I watch my oil pressure. Hopefully that will keep me out of trouble. The engine runs good, and has no problem pushing my boat along at 25-30mph.

This is my first I/O and it's been a real learing experience the past two season that I've had the boat. But the guys on here have been real helpful. Good Luck!

[Tim Bromund]

The typical theromstats for Mercruiser I/O's, at least somewhat older ones was 140 (or 143) deg for raw water cooled (open cooling system) and 160 deg for fresh water cooled (closed cooling system).

Tim

[Trap Jaw]

I saw those conversion kits listed on the internet. Trust me, the minute that charging system gives me one iota of a problem it's getting switched over.

We found out about all the issues after we bought it. In looking at what things might cost to fix/replace I came up with a different approach. If the motor ever takes a dump I'll switch it out for a new 4.3L V6. I just hope it never comes to that.

Even doing it that way it's still cheeper then having to buy a new outboard.

[YodaMage]

Closed system is basically not unlike a car. How hot does that get? Yup, anything below 220F wouldn't make me think twice under load. Anything under 170F at idle wouldn't make me blink either. Over 230 I'd start thinking about looking into pump, fluid, thermostat, etc...