Oil warning alarms and overheat alarm problem

Hi there ! I am having a very frustrating problem with my 1987 Mercury 175 relative to the alarms sounding. To let you know the history or what I have done thus far, see the below:
I have replaced the entire water pump system and changed the lower end gear lube as well. I have already replaced the Oil warning module, the motion sensor and the Oil resevoir cap sensor. Took it out and the alarm still sounds? What could possibly be the problem now? I believe the alarm is an overheat alarm this time as it was a steady single beeping. The previous time I had it out, it was the oil alarm with a steady beep beep???? That is why I replaced the warning module, motion sensor and Resevoiur cap sensor. The boat ran fine all day---Plenty of smoke indicating the engine was getting oil---Heads did not appear to be overheating as I was able to hold my hand on the head without getting burned. Ran it all day off and on with several runs at fulll throtle. If it was overheating, it would have seized up. Any ideas out there? I am at my witts end !

Thanks,
Eric

Re: Oil warning alarms and overheat alarm problem

If its not getting hot but the alarm is going off Try unplugging one water temp sender at a time to see if it stops. Or ohm them out to see if one is bad . Does it do it all the time or just after it warms up.

Re: Oil warning alarms and overheat alarm problem

On that engine you should have an OT sensor in each head water jacket....the plate that the spark plugs stick through. The tan and tan/blue wires connect to them. The sensors are mounted in the cover and ground to the cover which grounds to the block to function. Upon grounding (contacts close) they ground one side of the horn which has 12v across it when the key is on. The sensor is a single pole single throw (SPST) switch that closes normally around 195F. Your stats start opening at 143F. If you can keep your hand on the block you are well below 143F....a domestic hot water heater on the Normal setting is 140F for comparison.

I am assuming your horn is making a solid tone which is temp. Unplug both sensors (follow the wires to a connector) and see if that stops the problem. If so, isolate which is shorted and replace it.

Mark

Re: Oil warning alarms and overheat alarm problem

Groupergulper said:

If its not getting hot but the alarm is going off Try unplugging one water temp sender at a time to see if it stops. Or ohm them out to see if one is bad . Does it do it all the time or just after it warms up.

Click to expand...

Thank you for the response Groupergulper. The alarm appears to be an oil sensor warning as it is a constant beep and not a steady beep associated with overheat warnings. I also replaced the poppet valve while doing the water pump and lower end. Additionally, do you have any pictures of where the water temp sender (overheat sensor) is? When I started the engine, there was no alarm for about 5 minutes and when I accellerated to get off plane, the alarm went off. That is when I checked the temp of the head with my hand and I could hold it on the head without getting burned. There was plenty of smoke coming out of the exhaust so I know it is getting oil? Then I tried to disconnect each of the sensors to see if the alarm stopped. Resevoir cap sensor, motion sensor and warning module but the beeping was still present. The manual I have does not provide very good pictures of these parts since it is an on line manual. Any other thoughts?

Thanks,
Eric

Re: Oil warning alarms and overheat alarm problem

Texasmark said:

On that engine you should have an OT sensor in each head water jacket....the plate that the spark plugs stick through. The tan and tan/blue wires connect to them. The sensors are mounted in the cover and ground to the cover which grounds to the block to function. Upon grounding (contacts close) they ground one side of the horn which has 12v across it when the key is on. The sensor is a single pole single throw (SPST) switch that closes normally around 195F. Your stats start opening at 143F. If you can keep your hand on the block you are well below 143F....a domestic hot water heater on the Normal setting is 140F for comparison.

I am assuming your horn is making a solid tone which is temp. Unplug both sensors (follow the wires to a connector) and see if that stops the problem. If so, isolate which is shorted and replace it.

Mark

Click to expand...

Mark,

Thanks for the response. THe horn is a beeping warning indicating some sort of oil sensor warning based on what I have read in the manual. Do you have any pictures of the sensors you reference and how many of them are there? Are they behind each spark plug? I could not locate any tan and tan/blue wires on the heads where the spark plugs go into or anywhere nearby? I must be missing something. Other thoughts? By the way, I did replace both thermostats at the time I did the water pump in addition to the poppett valve.


Thanks
Eric

Re: Oil warning alarms and overheat alarm problem

big_eric said:

Mark,

Thanks for the response. THe horn is a beeping warning indicating some sort of oil sensor warning based on what I have read in the manual. Do you have any pictures of the sensors you reference and how many of them are there? Are they behind each spark plug? I could not locate any tan and tan/blue wires on the heads where the spark plugs go into or anywhere nearby? I must be missing something. Other thoughts? By the way, I did replace both thermostats at the time I did the water pump in addition to the poppett valve.


Thanks
Eric

Click to expand...

If you replaced the stats, the sensors are on the same plate that the stats mount to. There is nothing more than a wire and a little pear shaped cover and a screw. Remove the screw and cover and this little pellet comes out. I'm remembering that they were around the center cylinder in each bank.

I have no pics as it was my son's boat and he sold it. There is one wire per bank of 3 cyl and as I recall, the port side was solid tan and the starboard side was tan/light blue stripe.....supposedly to distinguish the port from starboard side.

If you are getting a beeping signal, not a constant tone, forget the OT. It's oil as you said.

Mark

Check and come back.
Mark

Re: Oil warning alarms and overheat alarm problem

Thank you again for your response Mark. As for the overheat sensors, I think I have found them. THey are just below Spark plug 1 and 3 with 1 being the starboard side. It has one little blak wires that grounds to a grounding hub above the switchboxes. THe port side looks a little different. There are no wires coming from it at all. It looks kind of like a spark plug in shape (albeit small). The end of it has threads with a small nut and washer, but nothing connected to it? The plate over this is a bit thicker too. I could take a picture of it and try to e-mail or text it to you if you provide me your e-mail address.
It is defintely a beeping warning and not a steady horn which would indicate it is the oil sensors or something within the oil injection system? Any other ideas knowing I have replaced the warning module unit, motion sensor and resevoir cap sensor. Also on the cooling side, Water Pump (complete kit), thermostats, poppett valve and lower end gear oil service. I am out of ideas? Any other thoughts Mark?

Thanks,
Eric

Re: Oil warning alarms and overheat alarm problem

Two sensors. Clyinders 1 and 2. 1 is starboard. 2 is port. Starboard sensor with one wire going to a small "term" screw on tha side of motor is tha only heat warning sensor. Make sure there are only two wires under that screw and they (wires AND screw holding 'em) are touching nothing else. Tha other sensor is for a heat guage. May or may not be used. Will not give you a beep in any form.
If you have change all that on tha oiler system with good parts, motor tank stayin' full and still gettin an alarm it may be a little deeper. Drive gear on tha crank. Pinion may not be turnin' fast enough to trip tha magnet. Could be tha switch box BUT you say its runnin' good. Sooooo, probably time ta get rid of tha oiler and pre-mix........jmo

25 years. Its lived a good life......

Re: Oil warning alarms and overheat alarm problem

Looks like I need to check that plastic gear. If that is not working, I guess it is time to premix due to the cost to fix that being around $1000-$1200. That is a bummer cause I just spent $450 on all the electric parts for the oil system. If I do go to premix how do I get the alarm to stop. Last time out, when the alarm went off, I disconnected the 3 wires to the module--Motion sensor (2wires), Resevoir cap (1 wire) and the alarm did not stop?