alarm buzzer is sounding

[gettinthere]

After running for several hours, the alarm buzzer sounds and the light comes on. Overheating right?

But I monitor the engine with a laser heat gun. I read the oil filter, mixing elbow, several spots on the heat exchanger and the thermostat housing.

All the readings are close to normal and lower than I have seen in the past when pushing the engine.

If I throttle back to idle, the alarm will stop after a minute or two. I can continue to run for several hours at half throttle with no alarm. I let it cool and throttled up 3 times over a 4 hour period and got the same result each time. Finished the day at half throttle for 2 hours.

So it seems I have an overheating issue but nothing appears overly hot. What gives?

Checked oil level, full. Checked coolant, up to normal level. I tend to think it's on the coolant side.

This is a perkins 4.154. TAD tells me not to overfill the coolant, it will just burp out. I did add extra coolant yesterday and afterwords found some in the collection pan under the engine. Water is coming out the exhaust at the back. But it would be hard to tell if it's the 'normal' amount. Strainer looks clean.
If I picked up growth, barnicles, in the seawater intake, why don't I see any rising temps?

 

[MitchM]

i'd pull your heat exchanger and check for a small blockage in one of the tubes. your symptom of ok temps at low rpms and alarm at higher rpms is consistent with your getting enough coolant flow at low rpms , but a small blockage will give these symptoms at high rpms. when you pull yr ht ex be sure to have some permatex or form-a-gasket or new oem gaskets to put it back together without a leak forming. and when you're puttng the blts back on to hold the ht ex covers, tighten slowly in a cross wise pattern - a little at 12 oclock 6 o clock 3 oclock 9 o clockthen a little more at 12 6 3 9 etc til you get a good seal. if you ever blew a raw w ater impeller sometimes tiny pieces of impeller travel into the back area of the ht ex and get stuck, blocking one or 2 tubes. thoat's enough to cause the overheat you describe.

 

[Bill Roosa]

Since you can make it "go away" by throttling down I'm thinking it is not a the overheat sensor.
Since it is only at higher power levels it sounds like a restriction in the raw water circuit. Could be:
Restriction in the thru hull (have to go overboard to see)
Collapsing hose or air leak on the suction side of the pump
HE scaled up or impeller part covering one of the HE tubes
Exhaust elbow carboned up at the water outlet

 

[Benny17441]

Yes check for obstructions in the raw water intake. The sensor is designed to go off well before any critical temperature is reached. Had a similar situation where a plastic bag was acting as a flap valve on the raw water intake. Throtle up and the bag would shut the intake flow and throtle down and the flow would resume. Luckily we had a temperature gauge on the boat and realized that we could continue to motor and monitor engine temperature which never got close to critical. Once at the dock we noticed the resticted water flow from the thru-hull and we blew the obstruction off by using compressed air. At the time we did not know it was a plastic bag but latter saw it foating next to the boat and put 2+2 togther.

 

[gettinthere]

This all sounds good except that when the alarm goes off, there are no high temps that I can detect.

 

[sailaway78]

Sending unit

Hit the sending unit with the laser and see what the temp is at the sending unit, when the buzzer goes off. It is very possible that the sending unit is a little off, and is going off at the slightly higher temp. when running the engine hard. All the other suggestions are good ones, but I always start with the simplest things first.

 

[All U Get]

Re: Sending unit

Have you checked out the Maine Sail's "Engine temp monitoring" How To series. I copied it all down to do my engine while it was running great. Nothing worse than a buzzer sounding and not having a clue what it actually means.
All U Get

 

[gettinthere]

Searched for the MS tutorial, can't find it with my droid. Can you link please?

Thanx

 

[All U Get]

Try,
http://www.pbase.com/mainecruising/engine_temp

All U Get

 

[gettinthere]

Thanks, I have been doing that, without the painted 'targets' and without a log of temps. Going from memory.
Only place I wasn't shooting was the sensors.

How easy would it be to just buy a new sensor at the local auto parts store? Are these things unique to each engine? Mine is a perkins 4.154. I'd order from TAD but we're cruising.

 

[gettinthere]

This is the temp sensor I think is the problem. I could replace it if I knew corresponding part numbers. Advanced auto is nearby and they have no way to cross reference a perkins 4.154. Btw, there are 2 on the engine, one for the guage and one for the alarm. The guage sensor is at the other end of the head, mounted to the thermostat housing and indicates 180 degrees.
Anyone know a generic part number? This one has 200f (temp) and 363-f.
Outside of threads measures about 3/4" perkins says they are 1/2" pipe thread.

 

[gettinthere]

This cross references to stewart warner 83307 but I still can't make a connection to anyone

 

[gettinthere]

Barring a miracle find, I plan on putting the old sensor back and getting underway. Next time the alarm goes off, I'll be sure to take a reading right on the sensor before pulling the wire (which will confirm it's that sensor and not the other coolant sensor or the 2 oil sensors). And I'll be careful to watch the guage until I can buy a new sensor & replace.

What do I put on the threads of the sensor to prevent a leak?

Thnx

 

[kloudie1]

Sealant.. MaineSail has a great recommendation for a Teflon based sealant.. Name escapes me .. it can be used on the exhaust ell also..

Edit: Yanmar temp switch part # 127610-91350 (on at 203F, off at 190F) would work if the threads are the same or you can find an adapter sleeve with correct threads..??

Another lead from Go2... http://www.go2marine.com/category/12122/engine-gauges-alarms-and-bells-for-boats.html

 

[All U Get]

This is the temp sensor I think is the problem. I could replace it if I knew corresponding part numbers. Advanced auto is nearby and they have no way to cross reference a perkins 4.154. Btw, there are 2 on the engine, one for the guage and one for the alarm. The guage sensor is at the other end of the head, mounted to the thermostat housing and indicates 180 degrees.
Anyone know a generic part number? This one has 200f (temp) and 363-f.
Outside of threads measures about 3/4" perkins says they are 1/2" pipe thread.

View attachment 50118

I believe my Perkins 4.236 may have the same sensor. In the parts book I have a 0650203 number for the sensor, Detroit Diesel (Perkins). A diesel mechanic should know better than I. If you clean the electrical connection it might help. Is it possible to dip it in some hot water to see if it functions? Another thought would be an air pocket right at the thermostat. MS had that in the temperature monitoring. I got some other books and I'll let you know if I find a different number.
All U Get

 

[All U Get]

Well, here's some numbers you may need someday.

All U Get

 

[gettinthere]

Here's another update:

Put the temp sensor back in. Ran the boat for about an hour & finally did get an alarm. The alarm sensor was reading 188 degrees with my heat gun when I pulled the wire and stopped the buzzing. The guage temp sensor mounted to the thermostat housing was reading 179 and the thermostat housing itself was at 181. The alarm sensor is at the other end of the head, at the rear of the engine (4 cylinder perkins 4.154 62 hp diesel).

The temp sensor has 200f stamped on it. I assume that is the temp when it triggers. Looks like the sensor is defective. Am I missing anything?

I'll order a new sensor in a week or so when I'm parked somewhere.

 

[kloudie1]

Sounds like you've got it.. Lots of marine diesels have a 160 F thermostat to keep the heat exchanger deposits to a minimum.. Ya might want to check the specification on your engine and make sure the correct thermostat is in there.

 

[Bill Roosa]

You could just test the switch, It is normally open below the set temp (200 F in this case) and closes above that temp.
Just put it in a pot of water with a thermometer on the stove and heat while measuring the resistance. When the resistance drops dramatically to almost nothing that is the temp.