1989 Force 85 HP

[bearcave86]

Hey guys I just bought a 1989 Cajun bass boat with a 1989 Force 85 HP engine. I can't find a serial number anywhere on the engine or transom and I need to order a thermostat and a new impeller. It seems there are several different engine variations and I don't want to order the wrong part. So far I have replaced the fuel lines, primer bulb, fuel filter, added a second fuel filter, drained old gas and added new gas, cleaned spark plugs and disassembled and cleaned carbs (filthy). I was able to get the engine started today and ran it for few seconds. I took out the thermostat to make sure it would open and it would not so I need a new one. I plan on changing the lower unit oil and thats really all i can think of to change. I also have a leak somewhere on the trim and tilt the engine slowly lowers after I raise it. So if anyone can point me in the right direction on the thermostat, impeller and trim/tilt rebuild kit I would very much appreciate it.

 

[Jiggz]

For your motor, the impeller and thermostat is basically the same as all other 89-85HP. The part number for the impeller is F694065 while the Thermostat is F664068. You can get substitute aftermarket ones from iboats.com. Just click on the boat parts & accessories and type in the part numbers and it will show you what is available. For the thermostat just make sure you get the 130 degree one.

 

[bearcave86]

Those part numbers are pulling up mercury part number 18-3553 and sierra 18-3017 are these correct? I also see a 18-3030 for the impeller?

 

[Jiggz]

That is correct. If you scroll down at the bottom of the page for each part number pulled up, it also tells you which OEM part # it replaces. Now this is with the assumption your LU is still the original one that came with the motor. To be sure, you might as well drop the lower unit and pull the old impeller and usually you can make comparison through the pictured item. You can do the same with the thermostat.

 

[bearcave86]

my thermostat looks similar to the sierra 18-3559 not the 18-3553. I guess I could order both. The 18-3559 says it opens at 110 degrees I thought these were suppose to open around 140 or 150 degrees.

 

[Jiggz]

Thermostats comes in different temp ratings although most common is 130. What you need depends on the local environment you will be operating the motor on. In warm waters it is better to use low temp t-stat like the 110 you mentioned to avoid overheating. On the otherhand in cold waters of the north, the usual 130 is recommended.

If the 18-3559 is similar to what you have, you should just order this one. In fact, that is the same one I have on my 89-125HP.

 

[bearcave86]

I'm in texas so a 110 would be better then thanks for the help Jiggz

 

[Jiggz]

As for the impeller, you might want to go with the 18-3017 sierra part #. Or you can just order both the 18-3017 and 18-3030 if you are not sure which one works for you since they are dirt cheap. But I'm quite sure the 18-3017 is the better fit for your motor. As soon as you find out it is a perfect fit, always have a spare in the garage for a broken impeller can stop your boating season in a heartbeat.

 

[Jiggz]

As for the tilt and trim repair, you might want to read through the sticky posts on top of the forum. There is one about T&T repairs and leak down procedures to identify where the leak is coming from.

 

[bearcave86]

well I just pulled the impeller and it was in about 10 pieces. I went ahead and ordered the thermostat, both impellers and some gaskets. The bolt under the exhaust snout was missing so I guess ill take one to lowes and see if I can find a match. Ill check the sticky thanks again for the help.

 

[Jiggz]

Just make sure no debris from the broken old impeller got stuck into the water tube or worse yet into the power head. Check the t-stat well for any debris and while over there stick a hose into the t-stat well to back flush the water ckt.

 

[bearcave86]

Jiggz I did as you said and the impeller is not pumping any water. I installed the tell tail to ensure that I get immediate water and nothing. I took the lower unit back off and the impeller is already ruined. Before i installed the lower unit i ran the garden hose through the lower unit to make sure it wasn't clogged. I then ran the hose from the thermostat housing and it does not appear to be clogged either. I seem to have a decent pressure running through the muffs but maybe its not enough. Ill have to order another impeller ill see if I can fill up a garbage can with water and maybe that will fix it. I also found out my overheat buzzer does not work so thats pretty awesome. Short of doing those things I'm not sure what else to do. Your input is apperciated.

Also to be clear when I installed the impeller i turned it counter clockwise into the housing so Im certain I installed it correctly.

 

[Jiggz]

Well if the new impeller is already on, you cannot back flush the unit. The only time you can back flush is if the lower unit is off and engine is not running. Whenever the engine is running, you need to provide cooling water from the water intakes of the lower unit. Sorry if I wasn't too clear on the last post. Anyways, install the new impeller and do a test run. Water should be coming out of the exhaust snout. Better yet, use a barrel or garbage can and dip in the LU while running it.

 

[bearcave86]

Let me start again I did not do a good job of explaining what I did. I first flushed the system with the impeller off, then I installed the new impeller and reinstalled the lower unit. After I reinstalled the lower unit and replaced the thermostat I tried running it on muffs and it didn't pump any water. So I took the lower unit back off to check the impeller and it was already ruined the fins have splits in them. I could not find any areas that seem to be blocked by debris and the inside of the impeller housing wasn't even wet. I don't think I had enough pressure on the muffs to force water into the impeller. Ill replace the impeller again and next time use a garbage can or my friends pond. Thanks

 

[Jiggz]

Oh OK. Anyways, with this Force model the water intakes are on the "bullet" of the LU making it very hard to fit muffs to make sure it is directing water into the impeller. The secret is as soon as the engine started, you should see water running out of the exhaust snout if not you need to reposition the muffs or increase water pressure. If you cannot restore water running out of the snout in less than 10 seconds from starting you need to shut down the motor. And then try again to reposition the muffs. I have the same system on a 89-125HP. DO NOT TRY TO REV THE MOTOR UNTIL YOU SEE WATER COMING OUT OF THE EXHAUST SNOUT OR YOU CAN DAMAGE THE IMPELLER AND MAYBE THE MOTOR ITSELF DUE TO OVERHEATING!

Also for muffs, I found out the best fit are those simple round ones with solid metal spring rods. Never use the rectangular ones or worse yet those with plastic spring rods. And finally, before installing the new impeller verify the inside of the housing is smooth as a glass. If not you will need to sand it down a little bit with very fine sand paper and finish it off with some polishing or metal polishing compound. And when first re-installing it use some liquid soap to make it install easier. Do not use grease or oil as this is detrimental to rubber.

 

[bearcave86]

I installed the new impeller and used a tub of water it took about 10 seconds for the water to come out of the tell tail. I think I'll just use the tub instead of the muffs. Now if I can just get the carbs tuned I'll be in . good shape. Thanks for all the help jiggz!