SOLVED: 1998 Force 120 Overheating

[bingbong]

I had an issue with overheating when I would run at over 2000rpm for more than a couple of minutes (alarm would go off). I replaced the impeller (made sure the key was in) and replaced the thermostat. Before there was no water coming from the peehole, but after the impeller swap it started flowing. I took the boat out today and got the same result again. I ran it until the alarm went off, then dropped it to about 1100 rpms and the alarm went off after about 30 seconds. While the alarm went off, I couldn't touch the thermostat housing because it was so hot. While keeping it under 2000 rpms, it stayed room temperature. I would appreciate any suggestions, I am losing my mind.

Thanks

 

[foodfisher]

Re: 1998 Force 120 Overheating

Re: 1998 Force 120 Overheating

You have a restriction somewhere in the cooling system. Take the thermostat completely out for a first test. May be the wrong one or installed wrong.

 

[bingbong]

Re: 1998 Force 120 Overheating

Re: 1998 Force 120 Overheating

You have a restriction somewhere in the cooling system. Take the thermostat completely out for a first test. May be the wrong one or installed wrong.

When I bought the thermostat, the outboard mechanic suggested I throw it in the garbage and not replace it, just leave it out. So I bought it anyway, but am leaving it out until I see an issue. He said that with the temperature here (Mississippi) that it wouldn't make a difference. I have tried both with and without, no change.

 

[bentle]

Re: 1998 Force 120 Overheating

Re: 1998 Force 120 Overheating

Sounds like a water flow restriction as already stated. With the lower off you can try a back flush through the therm. opening. If that doesn't work then pull the exhaust cover to clean out water passages. Also before all of that check the exhaust plate cover for any missing or loose bolts. They do sometimes loosen and fall down into the lower cowling. 70 inch pounds torque on those bolts.

 

[bingbong]

Re: 1998 Force 120 Overheating

Re: 1998 Force 120 Overheating

Forgive my ignorance, I'm new to owning/working on boats. Where is the exhaust cover and plate? I have a Clymer manual for this outboard which is how I have been getting by so far.. but want to be sure I'm pulling off the correct part. I have pulled the lower unit back off and will try the backflush tomorrow.

 

[bentle]

Re: 1998 Force 120 Overheating

Re: 1998 Force 120 Overheating

To try and make this easy.
Standing at the back of the motor looking at the spark plugs this is the cylinder head.
Now just to the left and left side is the exhaust plate. It has fins that run up and down but they are not to deep. Remember only 70 inch pounds on those bolts. If you do have to remove them then take them out very carefully turning really easy on them. I hear they can get stuck in there and be a real bugger to remove. Jerry seems to have some good advice on getting them out if they are stuck so hopefully he will read this and chime in here.

 

[Justinde]

Re: 1998 Force 120 Overheating

Re: 1998 Force 120 Overheating

Here is a post of my encounter with an exhaust port

http://forums.iboats.com/showthread.php?t=465794

I was lucky to break just 1 bolt, as you can see others went worse than me. Patirnce and a lot of penetrating oil/wd40 etc. My friend who is an auto mechanic helped. I am sure that his 'feel' for the bolts and tension was paramount in only breaking the 1- because I was the person who broke it.

The crud in the exhaust was crusted in like a rock. I bought a second hand onw from ebay(freshwater Wisconsin) for $50.00 plus postage. The gaskets were $35.00.

This, the link and sync and water pump, and now she goes well, except that one small problem with the tilt/trim- but I'm onto that!

Cheers

 

[jerryjerry05]

Re: 1998 Force 120 Overheating

Re: 1998 Force 120 Overheating

Your mechanic is giving the WRONG info.There is a reason they made the motor with a thermo!!!
They run better at a certain temp.
Like the others said it's possible a blockage has happened.
Now figuring out where it is.That's the fun part.
When you reinstalled the impeller and lower unit you sure you aligned the copper tube?

If it's been run in salt water it's possible the exhaust cover is clogged.
Like Justin said.be REALLLLLLLY careful try to undo the screws.
Location in Mississippi?
I use WD or PB Blaster to start working the screws loose.
Start spraying now(2 days)!! Then a bit of heat and a hammer to tap the screw heads.More heat and spray and tap and heat and tap and on and on!!
GENTLY,GENTLY try to unscrew them.They only have about 7ft#s of pressure.So if it won't budge more WD and heat and tap.
A small propane torch will usually work.
An acetelene torch will melt the alum.

 

[bingbong]

Re: 1998 Force 120 Overheating

Re: 1998 Force 120 Overheating

Ugh.. those pics look rough. The past owner tells me it hasn't been in saltwater and it doesn't look like it to me, but who knows. I took the lower unit back off and will re-check my work there first, back flush through the thermo hole ( and put the new one in). Hopefully that will fix it. I am honestly a little intimidated of messing with the exhaust area after hearing the stories.. nonetheless I will start spraying the bolts just in case.

Thanks guys

 

[bingbong]

Re: 1998 Force 120 Overheating

Re: 1998 Force 120 Overheating

Ok... took the water pump back off and re-installed for good measure. Everything looks good there. I went ahead and pulled the exhaust plate (was tough getting to those bottom bolts, is there an easy way to take the lower cowl off?). The plate itself looks extremely clean, however in the bottom left there were two sections filled with sand and pebbles. How much blockage would it take for it to overheat? It doesn't seem like much, but then again, I don't really know what I'm doing. Also, do I need to replace all of the gaskets? The outer one broke a little at the top, the metal one seems fine and the inner one is still stuck to the engine block pretty solid with no tears.

Thanks for the guidance!

 

[Justinde]

Re: 1998 Force 120 Overheating

Re: 1998 Force 120 Overheating

Replace the gaskets- at $35.00 might as well. just clean the old ones off the block/plate reall well.

any blockage is no good- look at mine

you'll find out on the lake!

 

[bingbong]

Re: 1998 Force 120 Overheating

Re: 1998 Force 120 Overheating

Ok...reading back through and watching videos on impeller installation, it has dawned on me that there was no copper tube when I pulled it off. I am also seeing some use a seal on top of the water pump housing that I don't have... is the seal on all models?

 

[bingbong]

Re: 1998 Force 120 Overheating

Re: 1998 Force 120 Overheating

Disregard copper tube comment.. it was lodged in the upper unit. I just never noticed. My Clymer manual doesn't show a seal around the shaft on top of the water pump housing, so I am assuming there isn't one. Does this sound correct?

 

[Justinde]

Re: 1998 Force 120 Overheating

Re: 1998 Force 120 Overheating

This thread should help....

http://forums.iboats.com/showthread.php?t=466213

 

[jerryjerry05]

Re: 1998 Force 120 Overheating

Re: 1998 Force 120 Overheating

Post a few pics of the pump.New and old.Pic always help.
These housings are made of pot metal or something like aluminum.
They can be in pretty rough shape but still work just fine.
You can lower the cowl but need to remove the shield on the mid section.
If you didn't align the copper tube it won't work right.
Try hooking a hose to the copper tube and turn the hose on.Not a lot of pressure needed.
Flash lite up in the housing.See if it's comming out around the seal???
The gaskets should be really replaced.
They can be found all over.Mercury dealers can get them.Or e-bay!

 

[bingbong]

Re: 1998 Force 120 Overheating

Re: 1998 Force 120 Overheating

Here is a picture of the water pump housing (I put it back together last night).

I just found the tube on the left last night and I'm wondering if there was supposed to be a seal at the base of the shaft on top of the housing. Like I said earlier, the Clymer manual doesnt show one, so I dont think one goes there. While I have everything torn apart, where else should I look for a blockage?

Thanks

 

[bentle]

Re: 1998 Force 120 Overheating

Re: 1998 Force 120 Overheating

Well from what I have found there is no seal above pump housing and on drive shaft.
However there should be a water tube seal that fits inside of the water outlet opening pump housing when lower is installed.
Most of the time it will be attached to the long water tube that feeds water to the motor.
If its missing then motor will overheat until replaced.

 

[bingbong]

Re: 1998 Force 120 Overheating

Re: 1998 Force 120 Overheating

Since I found sand and debris in my in the exhaust plate area, should I pull off the head as well and check it? I don't want to get in over my head, but I want to make sure I cover all my bases while I have it apart.

 

[pnwboat]

Re: 1998 Force 120 Overheating

Re: 1998 Force 120 Overheating

The head is easier to take off than the exhaust plate. Just need to torque the head bolts in the proper sequence when you put it back on, and re-torque after you run it at operating temperature for a while.

 

[bingbong]

Re: 1998 Force 120 Overheating

Re: 1998 Force 120 Overheating

Would I need to replace the head gasket after removing the head cover?