Mercury Water Pressure Gauge

[sportyinc]

I have a '72 1150 L6 motor.
There is only one 1/8" NPT hole in the head cover (approx. between spark plug 3 and 4) but I already have a water temp sending unit installed (extending 1" into the cover) in there.
Others in this forum have suggested cutting and tapping into the "Tell Tale" system but my manual does not talk about it or show it's location. Searching information about the "Tell Tale" system is useless.
I want to drill and tap a 1/8" NPT opening about 1/2" above the existing hole and install a fitting for the Water Pressure hose.
Since the head cover is only there to create a water chamber, and since the fitting wouldn't even extend into the chamber, I don't see any problems.
Has anyone out there successfully installed a Water Pressure gauge using the "Tell Tale" system or my way?
Any advice would be appreciated.

Thanks,
Sporty

 

[4JawChuck]

Re: Mercury Water Pressure Gauge

You just install the line with a tee into the telltale hose, follow the hose from the cowl outlet and you will find the head connection.

 

[sportyinc]

Re: Mercury Water Pressure Gauge

Thanks, I'll check that out.
Am I correct that my motor has 2 water outlets (NOT 1) on the back right below the cowl?
The ports I'm seeing are about 4-5 inches apart just below the lower cowl.

Thanks again,

Sporty

 

[Silvertip]

Re: Mercury Water Pressure Gauge

Those are bypass ports where exhaust and cooling water (usually a mist) exit while the boat is idling. Water pressure on the prop hub at idle causes exhaust to exit at the bypass ports. These have nothing to do with water pressure. Before you bugger up the water cover which would require a pipe tap, not a standard straight thread, simply "T" into the tell tale (if you have one). This is "the pisser" as some prefer to call it. If that doesn't work or there isn't one, then connecting to a new port on the water cover is the only choice. But I would not tap that close to the existing port as this invites cracking. Anywhere in the cover is acceptable but stay as far away from other bolts/ports.

 

[sportyinc]

Re: Mercury Water Pressure Gauge

Silvertip,
Thanks for that info. It is all starting to make sense.
I just purchased this motor to replace the Chrysler that overheated and died. I am trying to be very careful.
I went looking for the "tell tale" system. The two square ports I saw (I now know as "bypass" ports) didn't have a hose running to the block.
I did notice a very small (plastic?) nozzle on the starboard side of the lower cowl pointing down at a 45 degree angle.
I will check this out when I get a chance. If it is NOT a "tell tale" port, I will take your advice about tapping into the cylinder cover.

Thanks for your help. Much appreciated!

Sporty

 

[jeff_smith_0423]

Re: Mercury Water Pressure Gauge

Silvertip,

I did notice a very small (plastic?) nozzle on the starboard side of the lower cowl pointing down at a 45 degree angle.
I will check this out when I get a chance. If it is NOT a "tell tale" port, I will take your advice about tapping into the cylinder cover.

No question - without a doubt, that's your telltale. No tapping required.

 

[sportyinc]

Re: Mercury Water Pressure Gauge

That's great. Now I have a point to start from.

Thank you very much for everyone taking the time to help me with this problem.

sporty

 

[Moody Blue]

Re: Mercury Water Pressure Gauge

Don't waste your time tapping into the telltale line. The pressure is so low that the gauge needle will barely move.

I went thru this exercise earlier this summer. I ended up putting a brass "T" into the existing port on the water jacket cover. Connected the water pressure gauge to one side of the "T" and the temp sender to the other side. Gauge now reads about 2-3 psi at idle and 12-13 psi at WOT.

 

[sportyinc]

Re: Mercury Water Pressure Gauge

After hours of searching, I found an Auto Meter Cylinder Head Temp Sending Unit. Number 2259. It has NO probe sticking out past the threads.
It is 1/8" NPT and runs about $9.00.

I went to the Auto Meter web page and they state this sender can be used on any electrical temp gauge where room is a problem.

Using a 1/8" TEE, you can easily make a setup to hold the water pressure and the temp sending units.

Here is the link:
http://www.autometer.com/cat_accessoriesdetail.aspx?vid=33

I'll post back with the results.

sporty

 

[BLU LUNCH]

Re: Mercury Water Pressure Gauge

Scroll down this page there is a bunch of marine senders here......
http://www.livorsi.com/catalog/senders.htm

 

[sportyinc]

Re: Mercury Water Pressure Gauge

Thanks for the info.
The problem is the "probe" part that extends past the threads. The ones shown on the link you submitted, all have extensions past the threads.
If you put a sender with a "probe" (or extension) sticking out past the threads, it blocks the water flow to the water pressure fitting, resulting in no pressure.
The cylinder temp sending unit I found has NO probe extending past the threads. It can get water but does not block the water pressure fitting.
Hope it works.
Thanks for your input.

sporty

 

[Silvertip]

Re: Mercury Water Pressure Gauge

Better find out what the resistance range is for that temp sender. If it is not in the 33 - 240 ohm range it will not work with a marine temp gauge.

 

[sportyinc]

Re: Mercury Water Pressure Gauge

Thanks for the heads up, SilverTip,
The only specs I have been able to find so far state that the sender is good from 0-340 Degrees.
If I dig a little deeper, I should be able to find out the resistance.

Thanks again,
Sporty

 

[Silvertip]

Re: Mercury Water Pressure Gauge

Lots of senders are good for lots of temperature ranges. But they still need to be compatible with the gauge. None of the automotive senders are compatible with a marine temperature gauge. They are all in the 1000 ohm and above range.

 

[sportyinc]

Re: Mercury Water Pressure Gauge

Thanks.
I'm getting ready to research that sender and look for a marine sender that will fit my plumbing.
If worse comes to worse, I can drill and tap and use the sender I have now.

Sporty