how do i tell if my mercury is running correct temp.

[imported_Jjenkins]

just purchased 1978 mercury 175 outboard doesnt have a temp gauge how can i tell if its ok and can i install a temp gauge or is this nessasery.

 

[andy6374]

Re: how do i tell if my mercury is running correct temp.

This is a V6, right?

On your engine you have an overheat switch. When the engine overheats this grounds the overheat switch to the block and completes a circuit which SHOULD set off the alarm under your dash. Test this.


As to your question, I am not sure if you can tap into the cylinder head (preferably near combustion chamber of the 1 or 2 cylinder) and install a temp gauge. They are nice to have.

But better than a temp gauge is a water pressure gauge. This you can install. By paying attention to the water pressure at various RMPs you can quasi-monitor the engines temp. That is, if the water pressure is very low (like 1 psi) at WOT...you know you have problems and the alarm should probably sound.


Since you just purchased the engine, do you know it's maintenance history? If not, I HIGHLY recommend that you replace the waterpump and thermostats at a minimum. I'd also like to see you replace all the components of the pressure relief valve for good measure. That way you can start with a known working cooling system, and then you can get comfortable with the typical water pressure readings at various RPMs, so when an anomaly in water pressure occurs you can take appropriate action.

 

[Silvertip]

Re: how do i tell if my mercury is running correct temp.

A water pressure gauge will not tell you an engine is overheating. Lack of water pressure pressure will obviously cause overheating but good water pressure is not a guarantee the engine is not overheating. A stuck shut thermostat is just one example. Both a temp gauge and a water pressure gauge are desireable but I do agree if I have a choice of only one, I'll take the water pressure gauge and rely on the overheat sensor to warn of overtemp.. Several types of temp gauges are available. Although the gauge itself is similar in all types, the senders are not. There are three basic types. 1) Sender screws into the water jacket. A threaded hole must be available. No - it does not mount in the tell tale hole. 2) Sender mounts on a bracket bolted to the water cover. Paint is scraped from the cover and the sender is in contact with the cover. 3) A thermocouple attaches under a spark plug. The latter two styles can be referred to as cylinder head temperature gauges as they are monitoring the temperature of the water cover. The first is a true water temperature gauge.

 

[Dead Eye]

Re: how do i tell if my mercury is running correct temp.

Question: On all Mercs, all years, does the tell-tale temp represent the head temp? I know that the temps are not the same and can't determine if the head is too hot. I want to know say if the temp gague reads hot and the tell-tale is just warm then the head temp is OK. What should the tell-tale temp be on an idling motor?
Thanks, John
Don't mean to hi-jack thread but i think the answers may help

 

[andy6374]

Re: how do i tell if my mercury is running correct temp.

What I know for sure:

On the mid 80's thru early 90's V6 Black Maxs, the water that gets routed to the tell-tale passes thru tstats before getting to the tell-tale pisser. So the tell-tale temperature is an indicator of water temps inside the top of the block.

No sure what the tell tale on older inlines or newer mercs is an indicator of (ie, whether it tells you block temps or just the fact that the impeller is pumping water).

 

[Silvertip]

Re: how do i tell if my mercury is running correct temp.

The tell tale has one purpose -- to indicate the water pump is working. Cylinder head temperature is a good way to keep tabs on engine temperature. The sender should be located as close to the spark plug as possible on the cylinder that runs the hottest. Installing a temp sender in the tell-tale is not recommended.

 

[Dead Eye]

Re: how do i tell if my mercury is running correct temp.

Do the newer Mercs say 2002 run water thru the t-stats before exiting the tell-tale, like the older mercs?
Dead Eye

 

[Texasmark]

Re: how do i tell if my mercury is running correct temp.

You guys need to go over to my two threads I added yesterday concerning just this.

There are some obvious misconceptions in this thread that need to be clarified for your own good.

Not all engines of one mfgr are alike in this regard. I know from the testing mentioned that Merc does different things, in different years, to the same and different hp engines.

But, it doesn't require a rocket scientist for you to figure out what yours it like. A close visual inspection will tell you real quick what you have and what you can expect.

If you have any questions, I'd be happy to kick it around with you. I like knowing what I have for two reasons: Peace of mind, and understanding what I see when the engine does something.

Mark

 

[Texasmark]

Re: how do i tell if my mercury is running correct temp.

The threads are in Outboard Non-repair Discussions.

Sorry.

Mark

 

[phatmanmike]

Re: how do i tell if my mercury is running correct temp.

older inline mercs did not have thermostats. once they started with the v6's thats when they started using thermos. thats why it takes so long for an inline 6 to start pissing, the water has to go up and around all 6 cylinders and the back out the pee hole.

on the v6s, merc actually makes stainless washers that are the exact size replacement so you can ditch your thermoststats. they are reducer washers. they keep the water pressur where it should be and eliminate the possibilty of your thermostat frezzing or clogging shut 18 miles from home when your out fishing!

 

[Miami Criminal Law]

Re: how do i tell if my mercury is running correct temp.

i have a 2 stoke 115 merc 1996. Is it a V6? of 4 cylinder? and is there a thermostat in my engine?

 

[Silvertip]

Re: how do i tell if my mercury is running correct temp.

Miami -- It's a four cylinder in-line engine and yes, you have a thermostat. To determine the number of cylinders you have, simply count the spark plugs. If all of the plugs in a vertical line the engine is considered an "in-line". If there are two banks of cylinders with two, three or even four plugs in each bank, its a V-4, V-6, or V-8 engine respectively.

 

[Miami Criminal Law]

Re: how do i tell if my mercury is running correct temp.

thanks for the post. Now I know. Of course count the spark plugs! THanks. I appreciate your kind answer to a silly question.