Need Help Troubleshooting Overheat Alarm

[JEESails]

I have an E-38 with a Universal 5432. My temperature alarm went off yesterday as I was heading out the channel in Olympia WA. Exhaust water flow was normal, temperature gage read normal, oil pressure was normal, fresh water coolant was full, no smoke in the exhaust, engine was running smooth, etc.

We shut it down and sailed for several hours and sailed back into the marina before starting it up again. The alarm came back on and stayed on as soon as we started it. It ran normal for the 10 minutes or so it took to get back into the slip, but the alarm kept buzzing. Nothing I checked seems to be amiss.

Has anyone experienced this? Could it just be a bad sensor or something? Any ideas about where I should start checking would be great. Thanks!

 

[tdtrimmer]

We have the same engine on our E38, 1981 and have had overheating problems in the past. There are a number of threads about that engine here on the Discussion List.

The following is how I would diagnose the problem:

1. Check the rubber impeller on the fresh water cooling pump. If it is missing a fin, check the plumbing, especially at the output of the pump for the missing fin.
2. The 5432 was supplied with a smaller than needed (2 inch) heat exchanger, at least in the early 80's. The exchanger becomes less efficient with age and needs to be cleaned out or replaced. We replaced the original with a 3 inch diameter exchanger and our heating problems were solved.
3. Check the exhaust manifold and exhaust tubing. With age, the tubing will tend to separate and the inner liner will collapse restricting the flow of exhaust gases resulting in excessive back pressure and the engine overheating. Likewise, rust in the manifold and in the fitting that connects the cooling water to the manifold will result in restricted flow.
4. Check the water intake thru-hull for blockage on the outside of the hull. Something like weeds or a plastic bag could be restricting water flow.
5. Check the hoses to the water heater. A loose hose connection could result in an air lock in the freshwater cooling system.
6. Check the cooling fluid level in the internal cooling system.
7. Check the temperature gauge while the engine is running. If the alarm is going off but the gauge shows the engine is not overheating, replace the temperature alarm sensor.

Tom
S/V Mistress 1981 E38

 

[Emerald]

Do make sure to check the sending unit. I went through this last summer. Most idiot light/buzzer type sending units are a simple make or break thermal switch with a single wire to them. The trick is figuring out what your water temperature is without a gauge. I pulled mine, put it in a pot of water with a thermometer and checked continuity as I heated the water. I would expect infinite resistance until you hit the too hot point. In the end, I upgraded the system by installing a temperature gauge in addition to the switch type sending unit. This way you can see what the engine is really doing, and monitor if you start running at a different temperature - it's the change from a baseline, even if within an "OK" operating range, that can be the tip-off to an impending larger problem.

 

[Tom Metzger]

If the alarm comes on as soon as you start the engine the chances are very good that you need to replace the temperature switch. You indicated that the temperature gauge read normal temperature so you don't have an overheating problem.

The hardest job might be finding the switch. There is also a sender for the gauge. Once you do, remove it (turn on the engine switch to make sure the alarm stopped) and take it to an auto parts store for a replacement.

It is very likely around the thermostat housing:
http://www.marinedieseldirect.com/catalogs/catalog_group.php?owner=mdd&page_ident=200146-32-33&model=M-40&manufacturer=Universal&title=Water%20Flange%20Group&quant_position=&catalog=200146&printparts=200146&printservice=200154&printoperators=200157&comment1=

 

[Ryan L]

Sorry to revive an old thread but I am having a similar (maybe exactly same) problem and was hoping you might have found a solution? Any info would be welcome and appreciated... Thank you!

I have an E-38 with a Universal 5432. My temperature alarm went off yesterday as I was heading out the channel in Olympia WA. Exhaust water flow was normal, temperature gage read normal, oil pressure was normal, fresh water coolant was full, no smoke in the exhaust, engine was running smooth, etc.

We shut it down and sailed for several hours and sailed back into the marina before starting it up again. The alarm came back on and stayed on as soon as we started it. It ran normal for the 10 minutes or so it took to get back into the slip, but the alarm kept buzzing. Nothing I checked seems to be amiss.

Has anyone experienced this? Could it just be a bad sensor or something? Any ideas about where I should start checking would be great. Thanks!

 

[Randy Rutledge]

Ryan you say the same condition? If the alarm sounds when you start the engine cold it is the sending unit as stated in thread #4. The only other thing could be a shorted wire to ground on the sending unit side of the alarm.

 

[Ryan L]

Randy- thanks for the info! The alarm does not start when the engine is cold but once it goes off it will continue to go off even if I stop and then restart the engine unless a certain amount of time passes (like 10-15 minutes estimated). When we were testing to try to trouble shoot the alarm I used an infrared thermometer to confirm engine temp was accurate at gauge (got to about 194 before alarm while we were pushing the engine at about 90% of max rpm). As for oil pressure, we have an accurate oil pressure gauge in line between the engine and the sender that was reading mid to low 20 psi at the time of alarm. I don't know how low the pressure can go before it's a problem but I assumed the alarm was due to oil pressure.

In an effort to test this I cut the wire from the oil pressure sender but alarm did not stop. Then I pulled the fuse at the engine instrument panel leading from the oil pressure gauge to the alarm. That stopped the alarm (duh) but then it restarted when I connected the fuse. The only way to stop the alarm at the panel (other than the fuse) was to disconnect the positive wire to the switch (the instruments are all wired together).

To add to the mystery our tachometer suddenly drops about 500+ rpms then won't read higher than 2200 even at WOT. I noticed this on a trip a few weeks ago but this was the first time I watched it happen. First noticed about 30-45 minutes into the trip while engine was at about 90%. Did not seem to be directly correlated to the alarm going off (it happened after alarm started). My theory is that somehow the alternator changed output when battery was topped off after it started the engine but I don't know much about how this stuff works...

Final possible clue- when I turn on the blower the temp and oil pressure gauge needles move few millimeters.

As for shorted wire on the sending unit I only see one wire from each sender. Should I be looking for the short from the actual alarm buzzer?

Any more info would be grateful appreciated! Thank you.

Ryan you say the same condition? If the alarm sounds when you start the engine cold it is the sending unit as stated in thread #4. The only other thing could be a shorted wire to ground on the sending unit side of the alarm.

 

[Randy Rutledge]

Ryan 194 sounds hot for the engine. I would check engine specs and I think you will find the operating range to be around 170. Looks like the alarm should sound if the fresh water temprature reaches 210. The exterior of the engine at 194 might be at a range when the freshwater has reached 210. I am not sure which will be higher the exterior of the cast iron head or the water. Looks like 5-10 psi oil pressure should keep the alarm off. In the Documents section of this site under engines near the bottom of the list there are engine manuals that could give help, they say the oil alarm is a pulsing alarm and the temp is a signal??? whatever that means, I guess solid.

If you disconnect the temp sending unit wire and that stops the alarm it is the sending unit or the engine is too hot.

Good luck

 

[Ryan L]

Thank you Randy. Yes, 194 is hot for the engine but I think will be a relatively easy fix. In addition to troubleshooting the alarm I was checking prop pitch with WOT runs which brought the temp up (but you're right, too high...) I have the engine and service manuals but did not see the alarm section. I'll check again. In the meantime you've given me some good ideas to check out.

Ryan 194 sounds hot for the engine. I would check engine specs and I think you will find the operating range to be around 170. Looks like the alarm should sound if the fresh water temprature reaches 210. The exterior of the engine at 194 might be at a range when the freshwater has reached 210. I am not sure which will be higher the exterior of the cast iron head or the water. Looks like 5-10 psi oil pressure should keep the alarm off. In the Documents section of this site under engines near the bottom of the list there are engine manuals that could give help, they say the oil alarm is a pulsing alarm and the temp is a signal??? whatever that means, I guess solid.

If you disconnect the temp sending unit wire and that stops the alarm it is the sending unit or the engine is too hot.

Good luck