1983 85HP: small bolt next to the spark plug hole, what is it for?

[Benz Mondi]

There is a small bolt one inch to the left and slightly lower than each spark plug hole. Next to cylinder 1, the over-heat sensor is in that spot. How about the for the other two cylinders, what are they there for? Can I use one of them to install a cylinder head temp sensor? thanx.

 

[jerryjerry05]

Re: 1983 85HP: small bolt next to the spark plug hole, what is it for?

The head, it has a water jacket on it.
The screws are whats holding it in place.
Along with the head bolts.
You might be able to use the screw.
Just be careful when removing.
If it breaks off it can be fun to remove and tap.
You have the temp gauge?
You can install a light in series with your alarm.
When/if you overheat it will light up.
That is if the sender is working.
Test the sender.

 

[Benz Mondi]

Re: 1983 85HP: small bolt next to the spark plug hole, what is it for?

The bolt came out very easily. Looked like it had some RTV on the threads. My thought is that I want to monitor the health of my motor by being able to see the temps not just be alerted when it’s already starting to cook (overheat). The alarm horn is plenty loud so I don’t need a flashing light. The challenge is the temp sender. I purchased a Faria surface mounted temp sender here. Because of the ridges in the head I had to make a holder that used the middle bolt to hold it firmly against the surface of the head (though the one that I received is being sent back and a replacement is already on the way… tested it with two brand new gauges and heated with hot water and then soldering iron and never got the needles to move). I just thought that perhaps the bolt in question would be available as a spot to bolt in a traditional internal temp sender. Since it can’t, my last option is to use a water temp sender and install it in line with the tell tale from the top of the head. I’ll report back when I receive the replacement sender.

 

[jerryjerry05]

Re: 1983 85HP: small bolt next to the spark plug hole, what is it for?

The gauge?? How about a pic of the sending unit?

 

[Jiggz]

Re: 1983 85HP: small bolt next to the spark plug hole, what is it for?

I think having a temp gauge to monitor the engine is quite cool. However, wouldn't it be better to monitor water pressure instead? Obviously having both is even better. But having a temp monitor is not preventive monitoring at all but more like a shutdown monitoring and doesn't necessarily avoid incurring damage to the engine. However, with a water pressure monitor or gauge it is more preventive in nature since as soon as the water pressure drops, you do the shutdown and investigate hopefully before the temp goes up too high. In fact, you can even place a low pressure switch in the ckt to shut down the engine if pressure goes too low but you will also need a time delay for starting.

 

[Benz Mondi]

Re: 1983 85HP: small bolt next to the spark plug hole, what is it for?

It?s amazing what you can see when you take a step back and take in the big picture?
I figured out what my problem is. I didn?t provide for an adequate Ground!. I?ll have to clip a wire with a ring connector onto the sensor tab and connect it directly to the bolt. I just tested it with test leads, a glass of cold water, a pot of hot water on the stove, and a digital thermometer. With a direct ground connection, the needle on the gauge moves as expected. My set up should work now.

Anyway, here is my set up and the holder I made. The sensor increases resistance as the temp increases. I enlarged the hole at the sensor head to allow the rubber isolator to keep the head from contacting the metal of the holder and grounding the sensor out. I made sure to pre-tension the holder by making the distance between the bends about an 1/8? short of the height from the bolt head and the sensor head. If I had to do it again, I would have made the tab at the bolt a little longer to allow for a socket to get around the bolt head. Clipping the stock sensor tab was to allow for the freedom to position the sensor between the ridges from the head.

Yes, I already have a water pressure gauge to go along with the Tell-tale. Once you have either you?ll never run naked again.

 

[jerryjerry05]

Re: 1983 85HP: small bolt next to the spark plug hole, what is it for?

Is it getting a good contact through the paint under the sensor.

 

[Benz Mondi]

Re: 1983 85HP: small bolt next to the spark plug hole, what is it for?

Is it getting a good contact through the paint under the sensor.

I didn't want to take that chance at an intermittent contact. That's why I added the ground wire.