mercury 200 overheating

[aquasport1998]

Beginning to understand why a friend laughed when I bought a boat and said "Bring Out Another Thousand." Changed Throttle and Gear cables to get my '98 Mercury 200 to go in gear. Felt like a million to get it done and see the prop spin. Put it in the water and didn't have enough thrust to move even though it was in gear. Pulled the prop and found spun hub. Got that replaced and re-installed. Was only out $100 for both fixes. Put her in the water to test and she did great. So we got up early this morning to load up and fish. Pulling away from the launch, the alarm sounded. Found that the motor was not peeing at all so figured it was the temp alarm.

When I bought the boat/motor last summer had the mechanic install new water pump and thermostats and impeller. Ran great last season and early this season (other than the gear problem).

So how do I check and see if I need a new water pump, impeller, stats? Is there something else I should think about? Is it something that I can do myself or should I take to a ----gulp---- mechanic?

Thanks for the help guys.

 

[j_martin]

Re: mercury 200 overheating

Beginning to understand why a friend laughed when I bought a boat and said "Bring Out Another Thousand." Changed Throttle and Gear cables to get my '98 Mercury 200 to go in gear. Felt like a million to get it done and see the prop spin. Put it in the water and didn't have enough thrust to move even though it was in gear. Pulled the prop and found spun hub. Got that replaced and re-installed. Was only out $100 for both fixes. Put her in the water to test and she did great. So we got up early this morning to load up and fish. Pulling away from the launch, the alarm sounded. Found that the motor was not peeing at all so figured it was the temp alarm.

When I bought the boat/motor last summer had the mechanic install new water pump and thermostats and impeller. Ran great last season and early this season (other than the gear problem).

So how do I check and see if I need a new water pump, impeller, stats? Is there something else I should think about? Is it something that I can do myself or should I take to a ----gulp---- mechanic?

Thanks for the help guys.

If you have "popped it off" without water supply, even for a few seconds, then the water pump is bad. I consider an impeller (minimum) is annual maintenance anyway.

I wouldn't consider running that engine without a working water pressure gauge. Lily pad over the water intake to hole in piston time is measured in seconds.

hope it helps
John

 

[gss036]

Re: mercury 200 overheating

Did you get a constant alarm (beeeeeeeeeeeeeeeeeeeeeeeep) or intermittent alarm, beep beep beep?

 

[aquasport1998]

Re: mercury 200 overheating

Thanks, John. It's going to the shop next week.

 

[aquasport1998]

Re: mercury 200 overheating

GSS, it was a constant alarm.
I decided to pull the lower unit before taking it to the shop.
Found the impeller was chewed up.
Bought replacement and installed impeller and now having trouble getting LU back on.
Did not put it in Reverse before I dropped lower unit (newbie mistake). Now having a heck of a time aligning the splines on the gear shaft.

Any suggestions?

 

[j_martin]

Re: mercury 200 overheating

GSS, it was a constant alarm.
I decided to pull the lower unit before taking it to the shop.
Found the impeller was chewed up.
Bought replacement and installed impeller and now having trouble getting LU back on.
Did not put it in Reverse before I dropped lower unit (newbie mistake). Now having a heck of a time aligning the splines on the gear shaft.

Any suggestions?

Neutral should work as long as both are in neutral. Sometimes they have an attitude.

If you're talking about aligning the driveshaft to the engine, have your first mate put a breaker bar on the flywheel nut and turn the engine a bit. Just be sure you pull all the plug wires first, pull the kill switch, and make sure the ignition is off.

hope it helps
john

 

[aquasport1998]

Re: mercury 200 overheating

Thanks, John. Got the LU installed. Put the hose on it to test and all went well. The motor was peeing and purring.

Then I put her in the water today...beautiful day on the Gulf. All went well in the short tests around the dock, so I headed out of the launch area. I got her up to speed and on plane and ran for about 5 minutes. The alarm went off again. Assuming it is something with the water pump again though motor continues to pee a good stream. Let it cool down, and motor seemed to run fine at low speed getting back to dock (probly shouldn't have run it, but knew I was getting water circulation). No alarms at low speed.

What am I missing? What should I check next? Thermostats? Is there a difference in alarm for the oil injector and the overheat? Probly should take her in to the mechanic, but darn I want to know how to fix it!

 

[JimSA]

Re: mercury 200 overheating

Thanks, John. Got the LU installed. Put the hose on it to test and all went well. The motor was peeing and purring.

Then I put her in the water today...beautiful day on the Gulf. All went well in the short tests around the dock, so I headed out of the launch area. I got her up to speed and on plane and ran for about 5 minutes. The alarm went off again. Assuming it is something with the water pump again though motor continues to pee a good stream. Let it cool down, and motor seemed to run fine at low speed getting back to dock (probly shouldn't have run it, but knew I was getting water circulation). No alarms at low speed.

What am I missing? What should I check next? Thermostats? Is there a difference in alarm for the oil injector and the overheat? Probly should take her in to the mechanic, but darn I want to know how to fix it!

If you figure this alarm thing out, please post it. I am having the same issue with my Merc 200 when it gets close to 5000 RPM.

 

[mxzeatr]

Re: mercury 200 overheating

When John and the other guru's around here say you need a fully functioning water pressure gauge they aren't kidding.

Its 40.00 for the kit, and it tells you a lot about your cooling system. Its by far the best 40.00 I've spent. I don't get an alarm on my boat, but the darned gauge is pegged at 3/4 most all the time. I was worried at first, but once I monitored water pressure it seems just fine.

 

[aquasport1998]

Re: mercury 200 overheating

Think I have figured it out....talked to several folks on here and local mechs, they say it's the poppet valve. Finally figured where it is, took the lower cowling off and got the @#$%@ bolts loose. They were pretty corroded from salt water. Seals were trashed and the diaphragm had a fair amount of salt build up. Cleaned everything up and installed a new diaphragm and seals. Now waiting for the weather to clear enough on a day that I have time to put it in the water and see if that really was the fix.

While working on it, figured out...no big surprise...that the water gauge was toast. So looks like that is the next thing to replace before I put her in the water again.

Thanks for the help guys. Will up date when I get back to shore...if I come back.

 

[aquasport1998]

Re: mercury 200 overheating

Okay...had to come back. Put in the water and she did great. Idled well and ran strong at low RPM. Got her up to speed -- 4000 rpm and did great for good while...10-15 minutes of running in the lake. Took her down the canal at about 4000 rpm and within 3 minutes got an alarm. Shut her down. waited 5 min or less, turned key and no alarm. Started up and slowly made way back to the lake. no alarms and strong stream out of the tell tale. Back in lake picked up some speed and ran her for another good 5-10 min at between 3k-4k rpm. So held my breath and ran her down the canal slowly picking up speed. Did great, ran a good 10 minutes on plane. Then an alarm. Shut her down, cooled her off and limped back to the dock.

So...what next? Yes, I know I need the water pressure gauge. After the water pressure gauge... Is there a way to adjust the poppet valve? Did I get it "too tight" or "too loose" when I installed it? I read some where that you could clip one of the rings on the poppet valve spring. What does that do for me, if anything? Would it be the thermostats? Or a bad sensor? At a loss here guys. Not a whole lot of pressure to get back on the water as our fishing is closed for a while, but spending the time I would be fishing working on the boat.

Any insight would be helpful.

 

[gonnabe]

Re: mercury 200 overheating

Not trying to hi-jack thread, but I've got same problem-only worse. My story, 1994 200 owned since new, water pressure gauge since new, personally done all service since new (water pump and t-stats every year, poppet every 3). Live on a shallow brackish water creek, I cannot get in slip without kicking up mud with no fresh water at dock to flush engine.
engine has been gradually running hotter over the years (temp gauge since new), tried an "acid flush" last year and problem got worse. Tried running today for first time now engine overheats to "alarm" after running or idle (used to run cool while running-only overheat at 1800-2000 rpm )
Looking for suggestions.

Sorry for hi-jack, but hopefully both of us can find the answer in one place

 

[j_martin]

Re: mercury 200 overheating

Not trying to hi-jack thread, but I've got same problem-only worse. My story, 1994 200 owned since new, water pressure gauge since new, personally done all service since new (water pump and t-stats every year, poppet every 3). Live on a shallow brackish water creek, I cannot get in slip without kicking up mud with no fresh water at dock to flush engine.
engine has been gradually running hotter over the years (temp gauge since new), tried an "acid flush" last year and problem got worse. Tried running today for first time now engine overheats to "alarm" after running or idle (used to run cool while running-only overheat at 1800-2000 rpm )
Looking for suggestions.

Sorry for hi-jack, but hopefully both of us can find the answer in one place

If you're sucking in mud then immediately shutting it down repeatedly, you would expect a baked build up to clog everything over time. I suggest you find some place else to park it, or shut it down and bring it in with a trolling motor. You need to tear it down and somehow clean out the cooling passages.

Perhaps a factor in the other one?

John

 

[pokman]

Re: mercury 200 overheating

I also have this problem with my 94 125 outboard. Can run all day till I get over 5000 rpms. Is there a step by step instruction somewhere or pics for replacing the poppet? Sorry to step in on your thread.

 

[klze]

Re: mercury 200 overheating

Perhaps a factor in the other one?

x2
check all water jackets, blow compressed air through every hole and line...

water is coming out, but how strong is the stream? that is why you need
the guage, or try cleanning passages first.

 

[gss036]

Re: mercury 200 overheating

aquasport1998 aquasport1998
After reading your post, I guess my first question would be, DID you get all the pieces from the IMPELLER out? If not, you may be getting pieces moving around or stuck blocking the water passages. The poppet will work just fine, you cannot get it too tight.

 

[aquasport1998]

Re: mercury 200 overheating

Thanks for all the insight guys. Update on where we are:

took poppet out and cut a loop off the spring as suggested in another thread. replaced poppet and lower cowling.

removed and tested thermostats. working fine. put them back in.

dropped lower unit to make sure all was well with the impeller and the water pump. all looked fine.

hooked water hose directly to the water intake and ran for a while. strong stream out of the tell tale. clamped off the line going to the tell tale to run water through the rest of the block. seemed to be moving through fine.

put it all together again. When putting together, noticed what appear to be a hairline crack in the housing of the water pump around the impeller near one of the screws. Left it because it was late at night and i was tired and not thinking clearly.

Put her in the water next morn to test. Ran hot again, and didn't go as long before running hot and ran hot at lower RPM.

So, here's what Im thinking.
1. go back to original spring on poppet.
2. install water pressure gauge.
3. install completely new water pump to eliminate possibility of leak.

Advisable to replace the water lines from the splitter that Ts off to the tell tale and then to thermo1, from thermo 1 to thermo 2. And also the one out of the poppet. Or just take them apart and blow compressed air through them? They are now secured to the fittings with plastic zip cords...that adequate or should I go with metal clamps?

Anything else?
Seems the issue of overheating at higher RPMs is a thing with some mercs 200hp and up. Not sure where else to turn except take her to a mech.

 

[aquasport1998]

Re: mercury 200 overheating

Thanks for all the help on here, folks. Finally was able to make the repairs/fixes last night and I put her in the water. Ran for 30+ minutes most of the time at 4k rpm. NO overheat alarm!

Here's what I did to get the fix. Not sure which piece or pieces did the trick or if it was just cumulative effect. But figure no harm in doing it all...would have done it eventually anyway.

1. Replace poppet valve diaphragm and seals (went back to original spring setting as well, no clipped ring--see further up post).
2. Replaced impeller
3. Replaced water pump housing, plate, and seals. (just a note here: I originally replaced ONLY the impeller. Made a rookie mistake and tightened the nuts holding the housing on too tight...hairline cracks in the housing. This may have been the cause of lost h2o pressure and overheating?).
4. Cleared water lines of any debris..both with water and compressed air.
5. Cleared water intake chamber in the lower unit of old impeller shreds (maybe this was impeding water intake and lessening water pressure causing overheating?)
6. Installed new water pressure gauge.

She ran beautifully and made me remember why I boat her to begin with.

And then when I was putting her back on the trailer, durned if I didn't have a flat tire! It's always something....but it's worth it. Right?

Thanks, again for the help! Happy boating.