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Ever since I repropped to bring my RPM's into spec (from 4300 up now to 5200) I am overheating at anything above 4500rpms. The motor is a 1994 Force 120. I have replaced the waterpump, housing, wear plate, gaskets, and impeller as well as the thermostat. I am still right where I started. Any suggestions on what to do next?
I am thinking that maybe the block is just covered in crap from 12yrs of use. It doesn't run too well off of earmuffs, so I don't think it has been getting a good rinse after every use. I think my next course of action is to sit it in a bucket of fresh water and Salt Away and let it run for a while. Is there any chance that might break down some of the crud in there?
double check reinstall old prop & run.maybe something wrong with the prop.make sure the bottom is clean back to water screens,also no new tranducers??????????
double check reinstall old prop & run.maybe something wrong with the prop.make sure the bottom is clean back to water screens,also no new tranducers??????????
I followed you up to the tansducers part. Are you talking about depth, speed, temp, etc transducers??? If so, nope, nothing has changed since the new prop, she should be getting the same water as before.
Defineately try the old prop on it...I went crazy with a mercruiser I/O a few years ago. I change props, it was an old style that i picked up. The boat started overheating, would be fine till I planed off then it would not pick up water. I don't know if it was turbulence or what, after changing the pump twice and thermostat I put the old prop on and it was fine.
__________________ Stratos 2500 wa
Twin 225 Johnsons
What is that sucking sound?
The only thing I don't like about going back to the old prop is the loss of RPM's. It puts me back down to 4300 at WOT, that is WAY below what the engine should be running at. And it was a dog out of the hole, load the boat up for a day out and it would take forever to get up and go. I guess worst case is I just don't run over 4500 and leave the new prop on...???
What made you think the old prop was creating the RPM problem?
The boat was really overpropped. It was a 13x19 prop, I dropped down to a 13x15 Cupped prop after talking with a local prop shop. Everything improved except for this overheat problem.
Check the height of the engine. If just an inch too high on the transom it will not pick up enough water. The extra 1000 RPM that your achieving probably also means your going faster thus less of your lower unit is in the water. Your engine manual should describe what height to install the engine. If thats not the problem, I would go with your original thought of flushing the system. I would double check the impeller and check for a blockage before doing so.
When over heating are you trimmed up or Down? If up, then see if it happens when trimmed down. Thats a quick way of determining if the engine is a bit high.
I will double check the engine height and trim issue, I don't think it really makes a difference trimmed up or down, but I will give it a shot. If it seems to make a difference then I will drop the motor down a notch. Thanks for the help.
I am going to give the salt away idea a shot. I contacted them regarding running it in a bucket and what ratio to use, they sent me a very nice email giving me some ideas to help break down the crud. If that doesn't work I may be off to the prop shot again.
Kajun - If I do, I will let you know how it works out.
I would also just try the old prop and see if it does it, you also just may have a enough blockage that it will only do it at the higher RPM. Not familiar with the motor but you may have thermostats or a poppit valve that could be causing the problem.
Did you put the spring in the wrong location. And did you actually check the head temp with a temp gun or pyrometer. Re-check the Tstat and make sure it can move off of it's seat. (like a popet valve would)
The teflon seals got put back in the pump, right?
You did the pump, or someone else?
Someone flipped the impeller over and put it back on in last time I had that problem.
That pump kit is the right one for a Force, right? Do not assume that it is because it is a Merc gearcase. It is not a 90/125 Merc.
Water pump was done by myself and someone who has be doing his for 16 years, so that shouldn't be a problem. Everything was replaced, except the housing (impeller, seals, wear plate). And its the right kit, pulled right out of the Merc parts manual after inserting my serial number (comes back as a 94 Force, not merc). Thermostat was replaced with brand new and is working fine, I even ran the motor with no thermostat to make sure it still wasn't the Tstat. Thanks for all of the ideas, I will give slowly working through all of them to find out what the heck is going wrong.
I just saw on another forum that a guy was having an overheating problem that nothing seemed to fix. He pulled a cylinder head and saw that the cooling passeges were all packed with sand.
I just saw on another forum that a guy was having an overheating problem that nothing seemed to fix. He pulled a cylinder head and saw that the cooling passeges were all packed with sand.
I am keeping my fingers crossed its not this serious. I am not looking forward to removing the 12 year old bolts from the block.
I just saw on another forum that a guy was having an overheating problem that nothing seemed to fix. He pulled a cylinder head and saw that the cooling passeges were all packed with sand.
that was ME! lol...but i was having the same problem as this guy before i hit that 2ft sand bar
I had a similar problem with a 115 yam. much money and time later found the cooling passage stopped up. I would try the other above suggestions before pulling the heads. If your motor has a poppit valve ck that .
Overheat Headache!!! 
