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Author Topic:   Engine Overheat
Drydock posted 06-08-2003 04:18 PM ET (US)   Profile for Drydock   Send Email to Drydock  
I have a 135hp Merc Optimax on an 18' Ventura. Today was running around the lake between 2000 and 4000 rpm for about 2 hours with out a problem. I stopped to pick up someone and take a short break. Turned engine off. It was off about 10 min. Restart and got underway. As soon as we got out of the 5 mph zone around the Marina I hit the throttle and received an overheat alarm about 15 seconds later. I throttled back and checked for telltale water flow and it was there. Shutdown engine and restarted. Alarm was silent. Water flow was OK for idle. Increased throttle again and another alarm. 10 to 15 seconds later. Engine temp guage indicated about midway but on the cool side.
I also checked intakes for clogging.
I idled back in and came home. (no further alarms at low rpm) Has this happened to any of you? Any tips or info before I take it down to get the service shops line on this.
Clark Roberts posted 06-09-2003 06:30 AM ET (US)     Profile for Clark Roberts  Send Email to Clark Roberts     
Dry, the 135 opti comes with 142 degree therostats (two) while most engines are equipped with approx 120 degree thermos. This only applies to idle as there is a spring loaded, pressure actuated bypass to route water around thermostats at speed. This high idle temp is necessary to achieve the three star emissions rating and can cause temporary overheat alarm at idle speed and usually just as you hit throttle up. My experience is that highest temps are at dead slow idle (about 600 rpm) and that idle in gear at 1200 rpm brings temp down significantly. I ran a 135 Opti for 2 yrs and installed a temp gauge for each cyl bank so I could monitor closely... as ambient water temp here runs above 90 degrees frequently. There are 120 degree thermostats available (be sure to get the stainless ones) that will bring idle temps down but could have some effect on the emissions, plug life etc.. I installed the 120's and no problems... Happy Whalin'... Clark... Spruce Creek Navy
Clark Roberts posted 06-09-2003 06:38 AM ET (US)     Profile for Clark Roberts  Send Email to Clark Roberts     
PS> the stock temp sensor (located atop the starboard cyl bank - and easily accessed) has a built in analog output. This signal is via the solid brown wire on sensor and all you have to do is hook up a temp gauge to this brown wire and, bingo, you can watch temp modulate with different conditions. The reading will be cyl head temp (as sensor is seated in a blind hole and not in contact with jacket/cooling water) which is the more meaningful reading vs. jacket water temp which is always hotter than the cyl head. blah,,, blah,, blah...etc..etdc...etc... will hang up now! happy Whalin'.. Clark..SCN
fno posted 06-09-2003 08:39 AM ET (US)     Profile for fno  Send Email to fno     
Clark, any thought on the same problem with a Merc 90 four stroke. No computer or smart gauges involved. I will check the thermostat temp rating though.
Clark Roberts posted 06-09-2003 01:37 PM ET (US)     Profile for Clark Roberts  Send Email to Clark Roberts     
fno, completely different engines/cooling systems! I have a 115 Merc EFI 4S and have a temp gauge and temp runs cooler at idle than at speed and there appears to be no thermostat bypass... Best to get a good analog gauge to keep an eye on temp... just good to know, at least for me... Happy Whalin'... Clark... Spruce Creek Navy
PS>I also have a cooling water press gauge since am running with a power jackplate..
Drydock posted 06-09-2003 08:29 PM ET (US)     Profile for Drydock  Send Email to Drydock     
Thanks for the info. I called several Merc Repair facilities today and no one can touch it until July 7th. But the one that spent the most time listening suspected a bad water pump impeller. (As far as I know its original, 4 years old) My last years service (all $480 of it) did not include an impeller change. Clark, It amazes me how much some of you guys know about these engines. I cannot even find a repair or service manual anywhere. How did you learn about the thermostat setup and the sensor wiring. I cannot even locate a decent service manual.
If I could get a reliable temp reading I might try running it and keeping an eye on it but otherwise I'm too chickens--t to run it with the high temp alarm on. The warrenty is gone and I reeely cannot afford a new motor. Besides, This one has been running pretty darn good since I recovered from a bad primer bulb. The dealer I took it to could not figure out why it would stall after a successful start. I found out from this forum that there were a bunch of bad primer bulbs so I went to the dealer and bought one. He of didn't think that could be the problem but I haven't had a stall since.
Thanks very much.
tully_mars posted 06-11-2003 10:38 PM ET (US)     Profile for tully_mars  Send Email to tully_mars     
An impeller change is fairly simple on these motors. I had never done one before and did both of my 150 EFI's this year, took about 2-3 hours total for both. I suggest you save the money and get a service manual for them and do it yourself. The book does a good job of describing what to do and how to remove and reinstall the foot.

Also helps to have a 2nd person handy on re-installing the foot, just easier to guide it on gently when realigning the shaft spline.

Tully Mars

Drydock posted 06-13-2003 02:40 AM ET (US)     Profile for Drydock  Send Email to Drydock     
Tully and Clark. What service manual do you use?
Clark Roberts posted 06-13-2003 06:30 PM ET (US)     Profile for Clark Roberts  Send Email to Clark Roberts     
Dry, never got a repair manual for my Opti as it was always under warranty... Clark
cmarques posted 06-15-2003 11:01 AM ET (US)     Profile for cmarques  Send Email to cmarques     
Could the alarm be the low oil alarm? If I remember right my salesman told me at least on the 90 Merc that the same alarm goes for low oil or overheating- most times i've found my oil level to be low when coming out of an idle zone and jumping on the throttle then sitting in the river filling oil reservoir with other boats flying by. I think when the boat rocks back and forth or going on plane it thinks oil is way low?
TRAFFICLAWYER posted 06-15-2003 01:40 PM ET (US)     Profile for TRAFFICLAWYER    
After 4 years a impeller AND water pump is in due for change.
Drydock posted 06-15-2003 03:09 PM ET (US)     Profile for Drydock  Send Email to Drydock     
Yea, I'm sure the next time the whaler is launched it will have a new water pump and impellar. If that is the problem I will be very satisfied. And this will have a happy ending.

I thought of oil also but I am 100% sure there was neither a low oil level alarm or an oil pump failure alarm. The alarm setup is a 4 sector indicator with an audible horn. There was no doubt it was the Engine High Temp alarm both times.

The mechanic at the dealer I called asked me if I pulled off the cowl and felt the engine to see if it was really hot. I did not do this and would not have had a reference since I've never done that at all with the engine up to temp and operating normally.
Have any of you done this? Would you be able to feel if the engine was overheating? Where would you place your hand?

Don't want to deviate from topic but this episode did make me wish I had a full set of instruments though. I would love to be able to monitor actual Oil pressure, Engine Temp, Water Temp and fuel flow. And just have the idiot lights for pump or sensor failures. If I keep the boat long enough I may try adding some of these indications.

lakeman posted 06-15-2003 07:28 PM ET (US)     Profile for lakeman  Send Email to lakeman     
Just got my new used opti 135 on my new/used dautless 18 had a complete service and new impeller, motor has less than 60 hrs on it (2000). While trying it out and running at 3000_4000 then to idle no problem. Ran boat at near max rpm for a while 3-5 min and went to idle, for a while, when I hit throtle the overheat horn went on temp was 165, when it got down to 155 is was ok, did this several times, off to the dealer I go still under warranty
Bigshot posted 06-16-2003 02:32 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Definately do a water pump, 90% sure it will cure your issues. Easy job to do. You do not have oil pressure so don't buy that guage:)
lakeman posted 06-19-2003 04:52 PM ET (US)     Profile for lakeman  Send Email to lakeman     
Just got a call on my 135 opti with the overheat problem. The computer read out is showning no over heat recorded. Every thing else is fine. They are running more test to see if sensors are bad.

bsmotril posted 06-23-2003 03:12 PM ET (US)     Profile for bsmotril  Send Email to bsmotril     
A loose battery cable will cause weird intermittent alarms on the Optis. I had a stipped battery stud that caused intermittent alarms to no end. Was driving me and the dealer nuts until we happened upon the battery. Replaced it, and no more faults. I had the same sympton where the CPU dump did not show any errors for the alarms.
lakeman posted 06-23-2003 09:53 PM ET (US)     Profile for lakeman  Send Email to lakeman     
I tried the motor and boat again today, first day without rain. We lowered the motor on the 18 Dauntless one hole and I put a SE Sport on it. I ran motor as before no overheating. The water temp was down about 15 degress with the rain. I hope lowering the motor one notch did the trick????????
Time and money will tell.
ivansfo posted 07-16-2003 06:23 PM ET (US)     Profile for ivansfo  Send Email to ivansfo     
I ran into this problem 2 weeks ago with my 135 Optimax. The motor was idling at the lauch ramp for about 5 minutes. When I pulled away and pushed the throttle, the overhead alarm went off. Put it back in neutral and alarm stopped. Tried it again and the alarm went off again. Engine block temp read about 180 degrees. Water pressure read 0 when engine was at idle but it was [streaming] just fine out the back. Turned off the motor and restarted it. Rev'd it up to 2500rpm while out of gear and water pressure built up and engine cooled. Off we went fishing but found if I idled too long engine would overhead.

Took the boat to the dealer and they found low water pressure at idle as I suspected. They replaced water pump and popit valve. Going to pick up the boat tomorrow and try it this weekend.

One more thing. Buy an Optimax service manual on Ebay. Cost me about $20 and the info was very helpful. It will give you enough info to fix it yourself or at the very least know enough if the dealer is blowing smoke.


lhg posted 07-16-2003 06:57 PM ET (US)     Profile for lhg    
Mercury sells their complete service manuals, for any engine they have ever built, directly from them. Highly recommended.
jimh posted 07-16-2003 11:40 PM ET (US)     Profile for jimh  Send Email to jimh     
Got a Mercury shop manual for my 1976 50-HP Mercury. My Mercury dealer had it in stock, on the shelf. Cost $35.

I can't imagine there would be a problem to get a shop manual for an engine only a few years old.

Drydock posted 07-19-2003 01:54 AM ET (US)     Profile for Drydock  Send Email to Drydock     
New Impellar solved the problem. The impellar was original (1999) Bummer that it took so long to get it to a shop. The mechanic showed me the part and how the vanes on the pump had taken a set from non use so they were only pumping half the time (pretty obvious by inspection). Recommended an impellar change every year if you let your motor set idle for storage for 3 to 4 months. If you use it once or twice a month should make it an every two year project. Significant difference in the flow out the pee hole. Ran the engine for 4 hours after the change. All speeds, pulling skiers and at trolling speed and left it running at idle during a dock stop for 15 min just to see what happened. The Opti never made a burp and ran like a clock.
p.s. for what it's worth...the mechanic acknowledged some of the problems with the opti's. hate to drop brand names but they recommended using the mercury synthetic "optimax" DFI oil and Chevron gas because the additives seem to keep the engines cleaner. These guys are also a honda and Yamaha dealer and recommend Chevron in all these engines when available. (yes I did ask if the guy owned Chevron stock and the answer was no)

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