Merc 200 1981 - running hot??

RVAHA · Jul 24, 2003

I have about finished moving the Merc 200 off of a boat I purchased and installed it on my boat. I took it out and had very low amounts of water out of the pee hole. Also, I ran it for a while and temp gauge got close to 200 degrees. I had the dealer put in a new impeller. The old one looked OK. I ran it yesterday and pee hole is stronger, but not as strong as I thought it should be. Temp gauge was around 185 degrees when running. The sender is mounted on the starboard head. Is this normal?? I ran the same temp gauge on a Johnson 150 and it would idle at 140 degrees and run at 125 degrees. Does anyone know what the thermostats are normally set at?? Thanks for any help!! I don't want to lose this motor!! Also, I did not get any alarms.

profish00 · Jul 24, 2003

Re: Merc 200 1981 - running hot??

I think the T stats are 140

RVAHA · Jul 24, 2003

Re: Merc 200 1981 - running hot??

Thanks I'll take a close look at them. Rick

NICK JONES · Jul 24, 2003

Re: Merc 200 1981 - running hot??

Do you get that beep when you turn ignition on to confirm that the alarm system is working okay?That little piezo-electric beeper sometimes fails as does the alarm module on port side of motor. They may be nothing wrong , these do run hot, the tell tale will be too hot to hold your hand under for more than a second or so and the temp gauge way up at idle but it should drop back as the revs rise to around 2000 rpm. I think the tell tale exits after the stats so you don't get much out of it until the stats open up and also its hot compared to tell tales on other motors. Do you have a water pressure gauge ? If not I'd get one fitted.

RVAHA · Jul 25, 2003

Re: Merc 200 1981 - running hot??

Thanks for the reply Woodman. No, I don't have a water pressure gauge. Where does the sensor connect? Just looking at the telltale, it looks like it comes straight from the water pump, (bottom of the engine)but that may not be correct. I would like to see a stonger telltale, but that may just be my opinion. I'll check into the gauge. I think that I may pull both T stats and maybe replace them. I did not get a warning alarm. I did test the piezo beeper, and it is OK. Of course, not sure about the high temp sensor, or the control box. The dealer told me to throw the temp gauge in the trash, but I don't trust him. (The warranty runs out in 10 days) He gave me a fit about changing the water pump under warranty. As I said above, I used the same gauge and sender on the Johnson, and it never got above 140 on idle, 125 running. Of course, there may be a normal difference in the temp due to the location of the sender. On both motors, the sender was located on the heads. Thanks again for the help Woodman!! Rick

RVAHA · Jul 25, 2003

Re: Merc 200 1981 - running hot??

Woodman, I reread your post, and I do not get a beep when firing the engine up. I assumed that the high temp sensor just grounds the piezo when it gets to hot. (I grounded the wire from the engine to test the peizo. I think that its color is brown) Perhaps it feeds the alarm box which supplies the ground. On this year motor(1980 or 81), does an alarm box perform this function?? I need to get a book!! Thanks

RVAHA · Jul 26, 2003

Re: Merc 200 1981 - running hot??

I met with a new mechanic today and we pulled both thermostats. Both were corroded and appeared that they had been in saltwater. He recommended removing them and running the motor without the thermostats during the summer. I did this today and the boat ran at about 155 - 160 degrees, instead of the 190 to 205 with the thermostats. Everything else seemed to be fine.

robalofish · Jul 28, 2003

Re: Merc 200 1981 - running hot??

Put NEW thermostats back in. They also help to restrict the water flow over the heads so that the heat can be transferred to the water and out of the engine. They also help the engine to run at its recommended operating temp. Don't run without them. Rfish

profish00 · Jul 29, 2003

Re: Merc 200 1981 - running hot??

running without T stats will cause un even temps in the heads causing them to warp...... or you can drive it like you stole it.....

RVAHA · Aug 3, 2003

Re: Merc 200 1981 - running hot??

Thanks guys for the remarks. I had wandered if there were some good reasons to put them back in. I'll get a couple tommorow. Also, I purchased a water pressure gauge and am in the process of putting it in. Hopefully, between it and the temp gauge, I'll have some good info on the motor condition. Thanks, Rick

RVAHA · Aug 11, 2003

Re: Merc 200 1981 - running hot??

I put new T-stats in. Boat now runs at about 165 degrees according to temp gauge. I installed a (new)Teleflex dash mount water pressure gauge. It is connected at the top of the motor by removing a 3/4 " plug. The gauge is a 30 PSI. It goes full scale above 2000 RPM. Is this normal?? Any idea if it will hurt the gauge? Thanks

trumanlake · Aug 11, 2003

Re: Merc 200 1981 - running hot??

If the pressure gauge is pegged, check the poppet valve (lower starboard side of block).

RVAHA · Aug 12, 2003

Re: Merc 200 1981 - running hot??

Thanks, I'll check it. Is there just one, or is there one in each head (V6)?? Thanks again, Rick

RVAHA · Aug 12, 2003

Re: Merc 200 1981 - running hot??

Just pulled the poppit valve. Looks like there is just one, which is on the starboard side. It looks to be OK, not like the Tstats which were corroded. The spring seems to be OK. Any way to tell if OK? Or should I just change it anyway. Hopefully this may be causing the high pressure. If it doesn't, is there anything else that may cause the high pressure? (I assume that the new gauge is OK). Thanks for any help!! Rick

gss036 · Aug 12, 2003

Re: Merc 200 1981 - running hot??

You should be running 22 PSI at full throttle and about 143 degrees. I would think you have a restriction somewhere, maybe at the poppet valve. I would also think that the pressure guage would go inline after the t-stat. Check w/your mechanic to see for sure where you should hook it up to.

RVAHA · Aug 13, 2003

Re: Merc 200 1981 - running hot??

I took the poppit valve to the dealer. The parts man and I both think that there is nothing wrong with the valve. Essentially, it is a diapram valve with a spring behind it. Diaphram and spring both seem to be OK. What usually goes wrong with the valve?? I did run it on the muffs tonight. It appears to be the same as it was ( which may be OK) I did not get any water out the telltale except little squirts occasionally. Other posts seem to indicate that this may be normal until the TStats open. Any other idea where the high pressure may come?? As I said before, the pressure gauge is connected at a 3/4" plug that is located between the 2 heads. Both Tstats are new, and the temp sensor read around 165 degrees when running the other day. I put that sensor halfway up the starboard head. Am I making a big deal out of this?? Thanks for any help! I doing my best to try and make this engine last!! Thanks!!

RVAHA · Aug 17, 2003

Re: Merc 200 1981 - running hot??

ttt Any ideas on high pressure if the poppit valve is OK?? Thanks

RVAHA · Aug 24, 2003

Re: Merc 200 1981 - running hot??

Great news! I took another look at the poppit valve. It looked like it was squeezed close at all times. I took it to my mechanic. We compared it with another model and it looks like it was about 1/4" too long. Apparently, someone installed the wrong version of valve in the motor. I ran it this weekend. Normal operating pressure is around 12 pounds. At WOT, it is 20-22lbs. Also, the temp gauge now reads about 135 degrees. Telltale is now more consistent. In summary, it looks like the impeller was OK. The TStats were shot, and it had the wrong poppit valve. Thanks for all of the help!! The dealer told me to throw the temp gauge in the trash when it read 210 degrees! I'm glad that I didn't listen to him. Thanks again, Rick

merc 140 pontoon · Aug 24, 2003

Re: Merc 200 1981 - running hot??

"Poppet valve" is a new term for me. Does my 1974 Merc 140 have one? I can't find any info on poppet valves, online or in my Clymer manual. Steve

RVAHA · Aug 25, 2003

Re: Merc 200 1981 - running hot??

I'm guessing that it does, but I may be wrong. Do a search on poppit valves and you'll find some info. On my engine, it is on the starboard side of the power head at the back. It has a hose that connects to it. Rick

Merc 200 1981 - running hot??

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