OMC Cooling Issue

[KRH1326]

Hello Everybody....

Working on small issues now that the major ones are squared away.

On this setup, I have a new impeller and housing in the leg. It is routed as close to original as I can tell. Water comes from a hose barb on the Int Housing, and goes to the thermostat housing. From there it splits. It goes through the engine , and through the T stat (if open), and then into the front ports of the exhaust manifolds and out. If the T stat is closed, it bypasses engine, and rolls through the front ports of the exhaust manifolds and out.
I am a believer in pre-emptive maintenance. In addition to the original configuration, I have a crank mounted pump, that pumps directly into the rear ports of the manifolds, to assist with manifold and exhaust cooling. I do have a connection that I can divert it to the T stat housing , should the emergency arise.

Earlier this season, while running hard, the temp started climbing and heading for 220 degrees. I saw it happening and backed off the throttle, and she cooled off, and away I go without anymore temp climbs. This had happened once or twice max.
Today it happened again. Like I said, now I can focus on some of these other issues.

I opened up the T stat housing, while the engine was still hot, and pulled the T stat. It was pretty crapped up, and more importantly, CLOSED. I ran the boat back to mooring without the T stat, it ran at about 100 degrees.

At the mooring, at idle, I pulled the hose coming from leg impeller, and had a generous , copious flow. I checked the crank mount pump, and had the same.

I stopped and bought a new T stat, on the way home. I have some family commitments to stick to this afternoon, and can't go put it in right now.

I did however, play with this old one a little. I dropped it in a pot of stove top heated water. I don't know what temp exactly, but just when bubles were starting to form, prior to boiling. The T stat opened approx 1/4".

My questions for the iBoat crowd, is a multi-part one:

1) Just because I can open and close the old T stat with pre boiling water, does that mean that it was functioning on the boat?

2) Is there a way to test the circulation water pump, for flow, other than the obvious and messy way (and dangerous due to moving pulley and belt) of just pulling the big hose from pump?

3) Is it possible to be giving the engine too much raw water? Meaning that the additional pump is pressurizing the manifolds enough that I am impeding the flow from the open T stat to the manifolds? I really wouldn't think that the case, as water can freely blow out the exhaust. I did figure that you can't have too much cooling, but what do I know.


The two risers are new, and I had boiled and pressure washed (the insides) the manifolds, earlier this season. I had beautiful flow through all.

Normally, this boat idles thru 2000 rpm @ 140 degrees, and above 2000 rpm usually runs 160 to 180 degrees. Both exhaust risers are cool enough to place hands on for several minutes without major discomfort.

Tonight, after my brother returns, and takes his kids that I am watching, I am SUPPOSED to take my kids and wife across the bay, and have a quick cook out. I will not have the time (or desire with a full boat) to install the new T stat.

4) Will making a night run across the bay, loiter and back ( no start and stop, and start and stop running) harm my engine without a T stat?

5) Any other ideas, other than testing T stat and circulation pump?

Thanks Guys

 

[futz]

Re: OMC Cooling Issue

there is a aftermarket electronic manual for omc you can d/l for free at the top of the forum.

Or a seloc manual, will show the diagram and water flow, chart.

circulation pumps are standard. i think you have an obstruction such as a power steering cooler, or riser blocked up.

And why i say that no t-stat the temp gauge would not move at all.

 

[KRH1326]

Re: OMC Cooling Issue

Thanks Futz,

You are correct, the temp guage never moved.

I should have been paying more attention to the writing of my post.

After I pulled the T stat, and ran back to mooring, I should have stated that the temp remained at 100 degrees, which is the lowest that my temp guage reads. It could've been at 75 or 80 degrees for all I know. I do not have any kind of accessories, such as power steering or anything like it.

I am confident that I don't have any restriction in the manifolds or risers as they are new or recently overhauled and scoured. Both side manifolds and risers are "cool" to the touch, even when engine was running hot.

I am familiar with those manuals in Adults Only. I am working on obtaining a set of factory manuals that I can get Don S. to post there as well.

Thanks again

 

[totx]

Re: OMC Cooling Issue

Your old thermostat is opening to late and not enough.
This can cause over heating.

If it open at boiling 212 F, and only 1/4, should open at 140 F I think.

According to manual you can damage your engine driving without thermostat.

(Maybe not very likely to happen, a lot of people do) But not recommended...

 

[futz]

Re: OMC Cooling Issue

Not going to get into a debate about t-stats and if a person should have one in the motor.

But there is alot, i mean alot of people who don't have one in the motor.

 

[KRH1326]

Re: OMC Cooling Issue

Hi guys,

New T stat did the trick! Actually, the engine is running cooler than it ever had, in my possession, anyway.

When I bought the new T stat, I couldn't get an exact physically identicle one. There is only one marine supply in my general area, and they pretty much only carry "hot" selling items and Mercury stuff.

I matched my T stat up to one of the quicksilvers that was 140 degree rated. The only difference was that the merc one's outer retaining lip/ ring was slightly less in diameter than the "OMC/sierra/whatever" one. It did fit into the housing and did accept the rubber ring retainer.

Now boat idles and runs up to 1000-1500 rpm @ 120-130 degrees. Runs upto 3000 rpm @ 140 degrees. Niiice....

I would still like to find out some of the other answers I was looking for.

Can an engine get too much raw water? And is there a way to test a circulation pump?

Thanks guys

 

[futz]

Re: OMC Cooling Issue

the impeller of a omc sterndrive are mush, mush , larger then a merc, sterndrive.

The omc moves alot more water, but there is just so mush water that can be moved in a motor, because of the " piping limitation diameter " maybe i wrote that wrong, but the diameter of the pipe will only let so mush water per minute thru.