90 HP Johnson, replace temperature sensing?

The overtemperature switches on my 1993 J90TLATS cause just a little beep at the buzzer when shorted to the block, & I would like to replace them with sensors & gauge (Or maybe add it to them)<br /> Do I need two of each, sensor + gauge, or can I wire them together in some way to show the higher of two temperatures? Also, do the senders go into the same hole as the switches are now?<br /> I see the items I need in catalogs, but no help in assembly. Thanks for a great forum!<br /> Joe

Re: 90 HP Johnson, replace temperature sensing?

Joe, the temp sensors in each head contain bi-metal contacts. When heated to a certain temp., the contacts make up to put the warning circuit to ground. Thus the alarm blows. If your shorting the lead going into the wire harness and all your getting is just a "blip", I would take a look at the warning horn or it's wiring in the control box. It's just not for overheat. It also gives you warnings for the VRO system....if ya' still got it.<br /><br />Temp gages use thermocouples or RTD to gage engine temp. They are usually mounted on the outside of the block on the head. Problem is, with a four popper using two t-stats, you'll need a t-couple on each head and two gages.<br /><br />But I would see to the horn first IMHO.

Re: 90 HP Johnson, replace temperature sensing?

Thanks, OBJ. I have removed the VRO & are now pre-mixing. I'll take a look at the control box & horn.<br /> Joe

Re: 90 HP Johnson, replace temperature sensing?

Horn is OK, I would like to follow up with an actual gauge installation:<br />1) Will I have to drill & tap for the sender, or should there be a specific plugged hole? Is it 1/8 npt or 1/4 npt to match specific sender?<br />2) The Teleflex sender 52320s003 lists dual station models available - is that for each bank?<br /> Thanks

Re: 90 HP Johnson, replace temperature sensing?

The temperature sender you are looking at is not typically used on a two-stroke because of the heat range (100 - 240 degrees). On your engine the needle would hardly get off the 100 degree mark. Dual station means there are probably two instruments (one for each control position on the boat) but fed by the single sensor. A thermocouple senses temperature and changes its resistance accordingly. The device is fastened to head and does not stick into the water jacket.

Re: 90 HP Johnson, replace temperature sensing?

The temperature sender you are looking at is not typically used on a two-stroke because of the heat range (100 - 240 degrees). On your engine the needle would hardly get off the 100 degree mark. Dual station means there are probably two instruments (one for each control position on the boat) but fed by the single sensor. A thermocouple senses temperature and changes its resistance accordingly. The device is fastened to head and does not stick into the water jacket.

Re: 90 HP Johnson, replace temperature sensing?

Hi again Joe. Temp senders usually use a thermocouple mounted to the head. It is a mechanical contact meaning the sensor lays up against the head. Should be no drilling needed. If it's a dual station, I would assume that means two senders, one for each head.

Re: 90 HP Johnson, replace temperature sensing?

one sender for the starboard side and one sender for the port side. one gauge is all you need. wire the senders to a toggle switch to change from one side to the other. Thats what i did and it works perfect. they cannot read both sides at the same time unless you have two gauges. a waste of money in my book.