1987 Evinrude 90 HP flatback engine temp sender location?

[skibumm100]

Hi All,

Longtime lurker, first time poster. I just bought an 89 Astro Quickfire 18 FS fish-n-ski with an 87 Evinrude 90 HP VRO flatback. I am going through the boat and motor and trying to get everything working. I ordered a factory service manual today. I took it out last weekend after adding oil to the fuel tank to get 50:1 mix until I can be sure the VRO is working correctly and all of the warning buzzers and such are working. The first time out I was out for about an hour putting around. It's a small lake and it's a long, slow ride to get past the no wake zone. There was a lot of boat traffic and a lot of chop. It ran OK but I had no idea how to set the power trim. The tach was inop, the charging system didn't seem to work and the temperature gauge in the dash didn't seem to register. This boat originally came with a Merc 115 from the factory. I have run a 25 HP tiller deep-V aluminum before but this was my first time with anything bigger.

This weekend I cleaned the engine and found some chafed wiring and a couple of broken wires. The purple wire at the terminal strip was corroded and broken. I also found some other splices that were corroded and brittle. The tilt/trim plug had overheated and melted the plug in the past. I cleaned the terminals, put dielectric grease on them and put them back together. I took it out for a longer, faster ride last night to see if the oil tank level would drop a little. The tach worked and the charging system worked. It ran about 5200 RPM at WOT the way I had it trimmed. I had also read up on how to trim out a boat and the ride was much better. Water was flat, so that helps too.

It looks like the oil tank dropped maybe 1/4", maybe a little less. I burned a couple gallons of gas.

The question I have is the temp gauge. I did not see a sender for the gauge on the engine block. Does it have one? Is the gauge a left over from the Merc? The overheat switches both sound the buzzer under the dash. I grounded each switch and it rang the buzzer. The pisser seems fine although the two banks don't seem to be the same temperature by feel. Port bank is warm, starboard is cooler. Probably need to do the t-stats and water pump.

I need to change some of the clamps on the VRO hoses from tie wraps to ratchet clamps. . I need to test the VRO oil flow alarm, if there's a way. This is a 3-wire VRO.

Once my manual gets here I will start getting my parts list together. If someone can tell me if my motor has a sender or not, I can fix it in the meantime.

Thanks in advance,

Gregg

 

[MaPaHa]

Re: 1987 Evinrude 90 HP flatback engine temp sender location?

It sounds like mine I just posted about. If so, there is one on each head. It sounds like you found them and a short to ground makes the alarm go off. I imagine the gauge was for another motor but I’m not 100% sure.

 

[emdsapmgr]

Re: 1987 Evinrude 90 HP flatback engine temp sender location?

The engine has two overheat switches, one in each head. Either will sound the hot horn when the temp gets up to around 212. Horn will quit when the head gets back down to 175, which is still too hot. If you want to drive a temp gauge on the dash, you'll have to mount a sender compatible with the gauge. Most fabricate a Z bracket which will hold the flat face of the temp sender in contact with one of the two heads. That's fine to provide a general idea of the engine temp, recognizing that you are only measuring the head temp on one of the two heads.

 

[skibumm100]

Re: 1987 Evinrude 90 HP flatback engine temp sender location?

Thanks for the reply. Since it came with a 1989 115 Merc on it I should be able to use a sender for that. Once my shop manual arrives I should be all set on the motor. I may drill and tap the coolant passage and install two senders with a selector switch on the dash and just monitor the one that runs hottest. I need to find out if that is possible first.