Mercury gauge shows hot- but no other symptoms.

[DPForumDog]

We rarely use our 1995 Mercury 150HP 2.0 Black Max. We have owned the boat about 5 years and probably put less than 2 hours a year on the boat. The motor is original to the boat and only used in lake water. Yesterday Paw noticed that the gauge showed the engine was running hot. This may have been happening since day one and we just never noticed. The motor ran fine and we drove the 30 minutes back to our house with no problem. We never heard an alarm or buzzer. It takes 5 seconds for the tell tale hole to pee water and when it does it is very hot, but i read that is normal. Paw removed the two thermostats and ran the boat again and the gauge still showed it overheating .


1. Why would our buzzer/alarm not sound when it overheated?
2. What is normal for the temp gauge?
3. What it the best way to see if the motor is really overheating or just a gauge problem?
4. Is the Tell tale water supposed to be hot?
5. Should it take 5 or 10 seconds for tell-tale water to start peeing?
5. Any chance it is the poppit?
6.. Is there a way to check for debris (dirt dauber nest etc) in the system without tearing everything apart.?


I read that stoppages /clogs can partially blocking water flow and one website that said that clog debris was the number one cause of over heating. But another website said it was the water pump and another said the impeller.
We plan to change the impeller, pump, and two thermostats. and maybe the poppit.


This may or may not have anything to do with it, but Paw thinks the RPMS were too high, He had set the RPMS for 4000 but they went to 5000, but he attributed to excessive turbulence and current.
Any and all help appreciated,
Thanks in advance.
Granny DP
DPForumDog

 

[DPForumDog]

Has anyone ever heard of this scenario causing a boat to falsely show a motor is running hot when it is not?
".....I read where an Mechanic said in older motors,as the rpms increase,the wires to the temp gauge heat up and give a false reading. He said it shouldnt read more than 200 degrees,but the resistance in the older wiring may be the cause as to why it reads so high. His suggestion was to install a water pressure gauge and use that as a primary indictor of whether or not I am getting enough water flow. ...."

 

[alldodge]

1. Why would our buzzer/alarm not sound when it overheated?

It may not be over heating, the temp switch may not be working, or the alarm may not be working.
Does the alarm ever sound off?

3. What it the best way to see if the motor is really overheating or just a gauge problem?

Use a IR temp gun and measure the head temp where the temp sensor is located. Compare with the gauge

 

[Faztbullet]

Put a impeller in it and reinstall the t-stats...it will definitely run hot with stats removed

 

[DPForumDog]

I should have said that Paw removed the thermostats yesterday and it didnt change anything,

 

[DPForumDog]

Are we supposed to hear an alarm? We didnt. Where would an alarm be?
Thanks

 

[alldodge]

Alarm is under the helm in most cases. Look for the Tan/Blue wire at the motor. If you find the single wire on a connector just ground it with key ON and the alarm should sound

 

[Chris1956]

When was the last time the waterpump impeller was replaced? They do not last forever....even if you do not use the motor.

 

[racingdave]

How hot did the gauge tell you?Did it run hot at idle speeds or cruise speeds?

 

[QBhoy]

Intrigued by this gauge you have. Not often these have an engine temp gauge I think. I don’t have one on mine, I’m sure.

 

[Dukedog]

Intrigued by this gauge you have. Not often these have an engine temp gauge I think. I don’t have one on mine, I’m sure.

they were an option on most of tha pre 2000 v6 motors.. lotta guys added 'em later after purchase.. problem is their accuracy... seemed ta be all over tha place.. reason for tha ir gun to get tru temp to compare with gauge..

is your oiler still working or has it been switched ta pre-mix?.. reason for asking 'bout this is to find out if "buzzer" is good?.. if oiler is still intact, do you get tha self check beeps when key is turned on?..

to check over temp sensor and buzzer do this.. sensor in in starboard head.. will have "one" wire.. like daid will be tan/blue or possible solid tan.. with key "on" ground that wire anywhere on tha block.. should get a solid/continuous beep.. your "temp gauge" sensor will be a "two wire" (black, tan/blue) sensor in tha port head.....

 

[QBhoy]

they were an option on most of tha pre 2000 v6 motors.. lotta guys added 'em later after purchase.. problem is their accuracy... seemed ta be all over tha place.. reason for tha ir gun to get tru temp to compare with gauge..

is your oiler still working or has it been switched ta pre-mix?.. reason for asking 'bout this is to find out if "buzzer" is good?.. if oiler is still intact, do you get tha self check beeps when key is turned on?..

to check over temp sensor and buzzer do this.. sensor in in starboard head.. will have "one" wire.. like daid will be tan/blue or possible solid tan.. with key "on" ground that wire anywhere on tha block.. should get a solid/continuous beep.. your "temp gauge" sensor will be a "two wire" (black, tan/blue) sensor in tha port head.....

Thanks

no the oiler was the first thing to get thrown out. I’ve done that on the previous 2 merc V6 2 stroke before this too. Once bitten...twice as shy, as they say here. Not making that mistake again.

 

[DPForumDog]

Last weekend we removed the thermostats and reinstalled after the pot on the stove test comfirmed they were fine.

Success: This weekend we replaced the pump / impeller and our telltale temp went from 160F to luke warn. The engine temp was almost 200 vs 90-100 with the new pump. With the new pump/impeller the temp gauge never got above 15% versus 75% with the old pump.

Since changing out the pump worked we did not fool with the poppit. The rpms still go to 1200 even at idle speed but the boat runs great. We are still looking for the buzzer alarm.

correction: Paw told me we have a 1994 model not a 1994
Thanks everyone!

 

[Faztbullet]

Finally read post #4