[atomic1]

Howdy all,

I bought a used 40hp 1996 Mercury Mariner (4 cy) – Serial No. OG465134 that is stuck on the back of a 16’ Bass Tracker.

I mix my own oil/fuel (I don’t trust oil pumps), so I disconnected the low-oil alarm at the bottom of the oil reservoir.

My first time out, the overheat alarm started sounding after about 15 minuets of running (beeeeeeeeeeeeeeeeeeeeep). Plenty of water was coming out of the pee hole at all speeds and the engine block was relatively cool. I splashed water on the head, but it didn’t sizzle. I could even touch the head with my fingers and it wasn’t excessively hot. But since I’d rather be safe that sorry, I trailered it, took it home, and replaced the impeller. The old impeller looked fine (it was replaced 2 years ago) the gaskets looked fine; the whole lower unit looked fine.

I took it out this weekend and after about 15 minutes, I got the overheat alarm again. I immediately checked the temp by splashing water on the head (it didn’t sizzle) and touching it (not excessively hot). Again, plenty of water was coming out of the pee hole at all speeds. Then I ran it for 30 seconds at about ¾ throttle and manually checked the temp again. It was fine. Then I ran it for 1 minute, 3 minutes, 5 minutes, and 10 minutes at ¾ throttle. After each run I’d manually check the temp and each time, the head would not sizzle water and I could touch it without getting burned. If I unplugged tan wire at the sensor, the alarm would stop (like you would expect). And, just for fun, I plugged the oil reservoir back in and when I did, I got the low-oil alarm (since my oil reservoir is empty (beep-beep-beep-beep)).

As far as I can tell, this engine does not have a thermostat (someone please correct me if I’m wrong) so all it leaves is a bad sensor ($105.00). If anyone has any other suggestions, let me know. I don’t want to part with my $105.00 unless I have to.

I’m also considering not replacing the module, leaving the current one unplugged, and saving the $105.00, but I haven’t decided on that yet. If y’all have any suggestions about that, I’d be happy to hear them too.

Thanks guys,

Adam

P.S. Just a little note, the low-oil alarm on this motor is activated when the oil gets low, not when the oil pump stops working. So, if you have plenty of oil in the reservoir and your oil pump stops working, no oil gets mixed with the fuel, the oil level will stay the same, and the alarm won’t ever sound. Meanwhile, your engine is burning up……….$$$$$

[atomic1]

After talking with Neil over at Neil’s Boat Service in Cypress, Texas (nice guy BTW), I’ve decided to remove the sensor completely and not replace it. According to Neil, this sensor is the low-oil-alarm sensor only, and doesn’t have anything to do with the high-temp sensor. Since I mix my own fuel/oil, it is no longer needed. Additionally, removing it won’t disable the overheat alarm since the high-temp sensor is a separate component altogether.

I hope this helps someone else out down the line.

Adam