Force 90 Overheating AFTER Impeller replacement

[snowbrd84]

Alright, after all my frustration with this 1990 Force 90 I just bought, I thought I would share in case anyone else has the same issue...

Bought a 17' Bayliner Capri with a 1990 Force 90 and the guy said it just needed a new impeller. Tore the lower unit apart and replaced the impeller (however, the impeller in there looked brand new), kept getting over heat warning immediately upon putting it in gear in the water (did not overheat at idle....) While in the water, I took off the t-stat cover and removed the t-stat, started the motor, no water came out of the head, something is wrong... Called it a day and took it home. Pulled the lower unit, checked the impeller i just put it, looks perfect... Pulled the t-stat housing again, took my garden hose, stuck in on the water tube going up the motor leg that is normally fed by the water pump. Not a drop of water came out the t-stat housing and there was so much water pressure, i could barely hold the hose on... So I pulled the head off and it turns out, the guy i bought it from sucked in a TON of sand and completely clogged the water jackets feeding the head, the water jackets were literally jam packed with sand and shells + chunks of a chewed up impeller. I also pulled off the head cover and it had a ton of built up debri (calcification it looked like?) so i scraped it all off and, with some black RTV, reinstalled the head cover. After a new head gasket, t-stat, and spark plugs and some wrenching, i get it back out in the water. Immediately over heats again, my frustration at this point is at an all-time high, but no worries because this time its all me, put the new t-stat in backwards :facepalm: . Flipped it around at the ramp, and presto, boat runs great. This may be obvious for some, but the part of the t-stat the has the built in spring goes inside the t-stat cover, not inside the head.

So yeah, long story short, I would suggest that when replacing the impeller, especially if the old one got chewed up or you ran aground, pull the t-stat and shoot some water up there to make sure the passage is clear... I am guessing this is the reason he sold the boat and just decided to pass along the problem, because the impeller in there was new, while the old chewed up one was in the water jackets inside the head...

 

[emoney]

Re: Force 90 Overheating AFTER Impeller replacement

Good for you. Any time an outboard overheats, you're better off spending some quality time tracking down the source of the problem and never "assume" anything. Not sure who started the rumor that the impeller is about all there is to cooling these things, but lots of people think that's the case for some reason, lol.

Every time I drop the lower unit I try and if nothing else, visually inspect the water tube by shining a flashlight up there, along with the area where the driveshaft connects. You never know what's up there until you look. I had a dirt-dobber's nest in my water tube that I'm sure would've caused an issue had I not found it before putting it on the water. Another thing I'm a big fan of is getting one of those infrared digital thermometers to verify the operating temps at the head. Just because a motor pumps water doesn't mean it's cooling and I've never trusted the "put-your-hand-on-there-test". Doesn't seem that accurate to me, lol.

 

[snowbrd84]

Re: Force 90 Overheating AFTER Impeller replacement

Yeah everyone kept telling me that if it has a good impeller/key/housing etc, then it WILL NOT overheat. Well, it did, and it was... Thats why i figured i would post this, in case someone else ever has the same problem.

 

[Jiggz]

Re: Force 90 Overheating AFTER Impeller replacement

Your troubleshooting skills and processes are logical. The use of a pressurized garden hose to shoot straight into the water tube in the LU is one trick that will assure you have good water flow in the system. As you discovered, the water passages are all blocked hence the caused of overheating. I'm quite sure there is still a lot of calcification in other section of the cooling system. One way to clean this is use of citrous anhydrous acid or citric acid mix with hot water. Place it in a tub or trash can and run it through the system for at least 15 minutes while having a cheese cloth filter for the return to filter debris. When done, flush it with fresh water for 5 minutes to neutralized the acid.