Merc 502 Alarm
 

For the life of me, I can't remember what sensors are involved when the steady beeping alarm goes off. I know one is the outdrive reservoir level. What are the others? Had an alarm go off today at about 3500 rpm. Slowed down to about 1000 rpm and it went off. Throttled up and it went off again. Down and it went off. I went and checked the manifolds/risers. Left side cool as a cucumber. Starboard side too hot to hold on to. Cooled down with the slower rpm. The temp gauge was rock steady at 175* There was a lot of water from the exhaust tip, it was just hot. So can someone refresh me on what to check when the alarm goes off? Thanks

The normal others are:
Engine coolant overheat
Low oil pressure

If your motor is newer it can have others
What's your serial number?

It's a 2001 model EFi
Engine temp was 175* steady. Wonder if gauge is bad?
Oil pressure was 40 psi

Serial number is 0M005624

Possible to be the transom water intake fitting? Don't know the exact name.

Then your the same as mine (MEFI 3 and MPI)

The three listed in yours and my post are all there is. Running at 175 isn't bad, but your gauge may be the issue, but could also be the switch.

The temp switch is on the port side of the thermostat housing. Will have a plug with two wires coming from it. The gauge temp sender is on the other side with one wire. Next time the alarm sounds pull the plug and see if it stops. If it does, get a IR temp gun and see if your gauge is off and its getting hotter then the gauge is showing

It has run at 175 since i bought it. Hmmmm..... I will certainly check the switch and the sender next time up. I still have to find the cause of the hot manifolds. I am going to check the transom water inlet connector also.

Thanks.

Mine always ran around 165 until the more HP rebuild, and even now it runs no more then 170 when the water is warm. Then again gauges do wear out and are only as good as all their components

Your hot manifolds would be from the mans not getting enough water, and could also be having a restriction. Now if your in salt then could also include bravoits

Ok, so Bravoitis is not as common in freshwater motors? That is encouraging at least for now, as my motor is a freshwater motor. I will then check everything else and see if I can find any type of restirctions. Bravoitis check as a last resort. There has to be some type restriction as it will cool down when idling, like it's getting enough water at that point, but not enough at higher rpms. Thinking about possibly just changing the thermostat, temp gauge, sender and switch anyway. Other than the thermostat (changed in 16), all are 18 yrs old. Might be time.

Just changed my 1995 Rinker with Bravo for first time a few years ago and also did the Bravoits fix. Mine is also fresh water and did not need the change, it was clean.

My thinking is you have a pump and/or impeller issue. Idle will cool down better because it does need as much flow, and usually gets more water then it needs at higher rpm's. Look close at the pump housing and if the impeller springs out flly, or stays constricted some when removed

The alarm circuit and guages are totally separate from each other.
175* is a little high but not much. Mine will run that at WOT but closer to 165* otherwise.

Check the drive reservoir. Merc lube will turn thick like mud at the bottom and cause the sensor to stick.
Easiest way to test which one is to unplug each sensor individually when its going off.

More info here https://www.offshoreonly.com/forums/...questions.html

Thanks Griff.... I guess I should have said that the water temp is just below 175*. Not sure exactly if it's 170* or even 165*, but it rides just under 175*.

I get the drive reservoir, but I do't think that is the problem. It was full, but I understand where you are coming from and I will definitely check it.
Alarm went off as soon as I throttled down. Started again when I throttled back up and then off again as soon as I throttled down. Starboard manifold and riser were hotter than normal to the touch at first. After idling at 1200 rpm the manifolds cooled down to a more acceptable level.