Engine Alarm: SCR3200

[SummerBreeze]

Had an impeller on the port motor shred out last week, changed it...got most all of the spline material back from hoses. That motor is fine now. All of the sudden, I'm out this past weekend, both motors running fine, as I throttle up to put the boat on plane, the starboard engine alarm sounds between 2200-3500 RPM's. As soon as I kicked it slightly above 3500, no more alarm. Same occurrance of the alarm when I throttled down through the RPM's and fine again at idle...

Both motors showing between 175-200 degrees (as they have since I bought the boat 4 years ago), so no anomaly there, both motors have full oil and pressure reading around 50psi at throttle up..both motors with full complement of gear oil.

Ideas, my bright friends?

[SummerBreeze]

Same experience this weekend. I changed the impeller on the starboard motor just to be sure it wasnt that. I opened all the hoses at the thermostat housing to be sure there was no clogging. It was clear. Again, both motors are showing about 175 degrees at 3500 rpms. Heres a new piece of info, after shutting down the motors and opening the engine hatches, i noticed that risers on the port motor were hot, but not crazy hot...the starboard motor risers were much much hotter than the port. So, possibly the engines are cooling ok, but the problem is water flow at the exhaust manifolds. I really dont know how to proceed with troubleshooting at this point...i need some ideas.

[tackleshep]

After going through this when we bought out boat I have a hard time believing that you don't have a restriction in the line or the cooler somewhere. It could be as easy as it sensing a short water supply until you really get into it and then it pushing enough water not to make a difference to the sensor. We had impeller pieces caught in the oil cooler and had to be backflushed out. Just an idea.

[SummerBreeze]

I agree tshep...as do most others i talk to on this issue. I have never really followed the entire cooling system route from beginning to end, but im afraid im gonna have to get a good diagram of the 5.7 merc cooling system and just systematically go through each section checking for blockage.

[SummerBreeze]

Btw...where is the oil cooler?

[shrew]

The Alarm should be going off at 200 degrees. 212 is the boiling point of water and steam doesn't cool effieciently. You stated the engine temp is always between 175 and 200. At 175, I'd be happy. At 200 I would not. The question is, where are the temps exactly when the alarm goes off? If they are at 200, I would be a bit concerned. Also, is the motor that doesn't have hte alarm going off at relatively the same temp?

When was the last time the manifolds and heat exhcangers were replaced?

The only other thing I can think of that would cause the temp to rise, then the alarm to go off and the them the temps to go down and the alarm to stop at higher RPMs' would be a stiking or malfunctioning thermostat. A thermostat stuck closed, that then finally opens (albeit late) could account for this type of behavior.

[SummerBreeze]

Shrew...I misspoke when I said they ran between 175-200. Both port and starboard motors are showing 175 degrees at the gauges when the alarm goes off on the starboard motor. Neither gauge goes above 175-180.

I d/led a copy of the water flow diagram for the 5.7 merc I have. Three areas I have not checked for blockage are 1.The elbow fittings at the manifolds 2.The power steering cooler fitting 3.The fuel cooler. So....I'm going to buy a new thermostat today and when I go up to the marina tomorrow, I will immediately replace the thermostat and check each of those above mentioned areas for blockage. If I still have an issue...then ???

The heat exchangers/manifolds have never been changed and the boat is a 1998 model. However, it has never seen salt water and lived on this freshwater lake its whole life, not sure if that makes a difference in due time for replacement.

Now...One caveat to this whole discussion. I have not removed the (ECT sensor)alarm sensor connector at the the thermostat to truly be sure that, in fact, the cooling system is the cause of the alarm...however oil and gear lube are at correct levels and the difference in temperature at the risers between the two engines is absolutely night and day.

[seapuppy]

personnally..i'd take the end caps off the heat exchangers before you buy a thermostat....since it's not going above that temp on the gauge...it's probably some sort of blockage in the HE or the other places...but the thermostat seems to be working fine...



SP

[shrew]

Agreed, if the temps never go above 175 to 180, then the thermostat is not the issue. I believe that should be a 165degree thermostat. This sounds like it is working fine. I would expect the water temp to correspond to teh engine alarm. Is it a constant tone, or some other pattern?

[SummerBreeze]

constant buzzer. Where does the heat exchanger live on the engine. I just looked one up online, and I don't recognize it...let alone know how to pop off the caps...lol.

[SummerBreeze]

actually, I know why I don't recognize the heat exchanger...because I don't have a closed cooling system.

[seapuppy]

should be right on the top/fwd engine ..caps are on the ends...looks like a tube with a radiator cap on it...



SP

[SummerBreeze]

o well...guess i'll hunt for blockages this weekend. Fyi, there are no heat exchangers on an open cooling system. I was able to garner that tidbit of info through a mechanic today, so no wonder that piece of hardware seemed alien to me.

[SummerBreeze]

Two words: frozen thermostat. Crisis averted, problem solved...over and out.

[seapuppy]

oh...I thought you had a closed fresh water system...sorry...my misunderstanding........glad it was simply the thermostat....thanks for posting the end of that.....


SP