1981 235 OMC temp gauge question

[Rickracer]

Where is the best place to drill and tap for the temp sender? I'm looking at the rectangular plate that covers the hole the regulator normally sits in on the later models, or there's about a 3/4" boss over to the starboard side of that that looks like it would be a likely location. Thanks in advance, :cool:

[Liqui-Fly]

12" long 3/4' spade bit right down through there. It will take care of all your problems hehe.
David

[Jeff_G]

You would want it on the hottest part of the motor the cylinder head near #1. That area is relatively cool and you could fry a powerhead long before any temperature change there.

[BarryStrawn]

I'm curious what others will say but I'm planning to put one in the top of each cylinder head right in front of the thermostat. A water flow diagram is attached and like Jeff says the top of the block doesn't seem to be the ideal location.

[Rickracer]

Right where the piss tube comes out of the exhaust housing, I put in a tee, sender on one side, piss tube on the other one, (keeping flow of hot water moving past sender)I would think this would provide pretty near the warmest water in the motor to the temp sender. I'll let ya know how it works. I'm gonna put the water pressure fitting in the boss on top. :cool:

[BarryStrawn]

Let us know how it works out. I'm fairly certain that's just about the coldest water in the engine.

[Rickracer]

Not enough clearance from the back of the cowl.:rolleyes:

[racer]

Barry has the right spot

[Rickracer]

After examining the flow diagram, and looking over this motor in that light, I have come to that conclusion as well. Thanks for the hint Barry and AL, I'll be driling and tapping tomorrow. :cool:

[B.Leonard]

According to the diagram, the hottest spot would be the bottom of the head. Why not put it there (haven't checked to see if there is room)?Mine sits on the outside on #3 cyl.

Don't expect that temp sender to warn you of a piston meltdown. That piston will have melted and cooled down before that sender gets a clue as to what's going on, and even then it may never know.

It is extra info as to whats going on under the cowl though.

-BL

[Jeff_G]

On top of the cylinder head is OK but not optimum. The waret is still cold until it flows through the thermostat. You want to put it in the hottest stream of water. #1 cyl. in the water jacket on the back of the head.

[BarryStrawn]

Hey Jeff,

Can you clarify? I don't understand what you are saying about water not being heated until it flows through the thermostat. Until the water in front of the thermostat is warmed by the engine, the thermostat will not open.

My thinking is that right in front of the thermostat would see good temp without being effected by whether the thermostat was open or closed.

Barry

[Jeff_G]

The easiest place to check with a pyrometer or thermomelt stick is the top of the cylinder head. It is probably the easiest place to place the screw in type switch. Although the water jacket is the hottest part of the water after it flows through the thermostat. The water is restricted by the thermostat until it heats up. That's why the temperature guages that direct read the water jacket temperature, surface type, are on the jacket. The water before the thermostat is cooler than after. Look at the diagram, blue is cool water and red hot (relatively). Barry you are correct on putting a switch on each cyl head. You are also right in you will see the least amount of fluctuation there. B. Leonard is right in that a guage will not necessarily warn you of a meltdown until too late. Much more important is a water pressure gauge to ensure you are pumping.

[racer]

The problem with after the thermo is the water is freefalling down the back of the head, and block temp is more important than head is we are concerned about longevity. The biggest thing here is to watch for changes in temp were ever you decide to put it. I run temp probes in both locationson the dyno and once the thermo opens they are only a couple of degrees apart. The flow color on the diagram is to show before and after thermo only.

Alan Stoker

[BarryStrawn]

Thanks Jeff, you just lost me with the "cold" water part. I've never bothered with more than a pressure gauge before but I was changing the dash and thought why not. Mostly just to see when she is warmed up. I thought one for each side made sense since the flow is divided before it starts cooling the engine.

Barry

[Rickracer]

Should I run the stats or restrictors, and if so, what size restriction? Right now I just have the centers clipped out of the stats. Thanks

[racer]

I always left the stats and valves, at speed it blows open the valves so its like the stats are removed, but they idle better and warm up quicker, much better if running forged pistons.

[Talon2.5]

good point warming up a forged piston motor with thermostats installed