Merc overheat alarm randomly at idle

[Tyler Schmidt]

Motor is a 2.5L 2004 XR6 (carbed 150) At idle speed throughout the day I began to throw an overheat alarm (single continuous beeeeeeep) but would not throw one operating at higher rpms. Thermostats and water pump (all components) are less than 2 months old. PSI at WOT is 18-22, at 1k rpm it is 7-10psi and below 1k rpms it drops below 4-6psi. I would throw the alarm at the 600-1200rpm range. I pulled the stats and the rubber gasket is intact. Ran it without the thermostats on the hose and water flowed freely out of the left side of the water jacket while it ran slowly out of the right side. I could plug the left side with my thumb and the water would flow well out of the right side of the jacket.

 

Any ideas what the issue could be? I couldn't replicate the alarm on the hose, idled at 5-7psi. I use the boat 1 or 2 times a week, 6 days ago no alarm, 2 days ago it went off about 6 or 7 times, and 0 times in the driveway yesterday.

I had someone tell me that a single continuous beep could also be a oil alarm but I was under the impression that is "beep beep beep beep"?

 

 

[jboutfishn]

I would replace the water pump impeller.

[Tyler Schmidt]

7 hours ago, jboutfishn said:

I would replace the water pump impeller.

It's 2 months old, the housing, the gaskets, the impeller, everything new oem product. My water pressure has not changed, indicating the pump is working as intended. I will be checking the overheat sensor to see if its operating correctly, then check the poppet valve on the lower starboard side of the block before I drop the LU again. I hate trying to line everything up and put it back in by myself. I will be inspecting the water pump last.

[WRB]

May not be a water issue, could be an oil problem. The pee hole only shows the water pump is working, the water to the power head is via the thermoset opening after the engine warms up.

Tom

 

[webertime]

You checked all the oil sensors too?  Pump working?

[Tyler Schmidt]

38 minutes ago, webertime said:

You checked all the oil sensors too?  Pump working?

The only way to test to see if its pumping oil is to run it on a remote tank, per the service manual, and I do not have one. I did check the continuity of the leads on the oil sensor, 0 ohms, which is correct according the service manual. I also took apart the oil pump, the O rings, bushings were intact, the gear teeth and bore were clean of debris and free of damage, residual oil in there as well. Haven't checked the continuity from the leads on the overheat sensor yet. I'm going to drop the LU and go through the water pump system to see if I had something bite the dust. Before I do that I am going to run it on a tub of water to try to recreate the alarm. I think running it on the hose was forcing water through the motor. I've been busy at work, or it has been dumping rain.  

[webertime]

I have the same issue and mine appears to be electrical, So I am chasing that gremlin...

[Tyler Schmidt]

@webertime I just re-tested my thermostats and found one of them was only opening about 1/3 of the way. The stats control water flow at a low rpm range while the poppet valve controls water flow at higher rpms. I was getting the appropriate amount of water while running but when I would get off pad and graph around I wouldn't have enough water circulating in the water jacket due to only having 1 and 1/3 of the stats open. Causing an intermittent overheat alarm Going to pick a new stat up tomorrow and go fishing Tuesday. I did test my overheat sensor as well, continuity was 0 ohms, working as intended.