Operating temperature 1992 200 HP Mercury

[jdupree]

Could you tell me what the normal operating temperature should be for this motor? I just installed a visible teleflex gauge to monitor temperature. My motor has a factory sending unit installed on the port side. The wire is grey and is just 1 wire. The gauge is showing over 200 deg once you slow down from WOT. I have tested the overheat alarm and it works. The book shows that the overheat alarm goes off at around 190deg. The tell tale is very warm to the touch but you can hold your hand under it. The water pump, t-stats, impellor were replaced recently within the last 2 years. Just needed to know if I should be concerned about what the gauge shows, or if I even have the right gauge or not. Motor does run great. I just don't think the motor is running at over 200deg. Thanks in advance for the suggestions.

 

[gss036]

Re: Operating temperature 1992 200 HP Mercury

On my 1989 Merc 200 HP, the temp sender is located on the (left) port head and has 2 wires. One goes directly to ground, the other works it way to the guage. Since it is right below the thermostat, which opens at 143 degrees, I would assume the temp is close to that. The average hot water tank in your house is set somewhere around 110-120 degrees. The teleflex guage works on restiance sent out by the sender. I chaged my sender and guage last year and was getting high readings with the teleflex sender, went back to the Mercury sender which put it back into what, I considered, the proper range on the guage. I doubt very seriously, that it is running at 200 degrees, you definately would not keep your hand in the stream(steam).
The overheat alram in on the (right) starboard side and has one single wire which works its way to the buzzer, for a constant sound. The button syle overheat sender "pops" and makes contact, completeing the circuit, causing the alarm to sound, when it cools down it resets itself.

 

[jdupree]

Re: Operating temperature 1992 200 HP Mercury

On my 1989 Merc 200 HP, the temp sender is located on the (left) port head and has 2 wires. One goes directly to ground, the other works it way to the guage. Since it is right below the thermostat, which opens at 143 degrees, I would assume the temp is close to that. The average hot water tank in your house is set somewhere around 110-120 degrees. The teleflex guage works on restiance sent out by the sender. I chaged my sender and guage last year and was getting high readings with the teleflex sender, went back to the Mercury sender which put it back into what, I considered, the proper range on the guage. I doubt very seriously, that it is running at 200 degrees, you definately would not keep your hand in the stream(steam).
The overheat alram in on the (right) starboard side and has one single wire which works its way to the buzzer, for a constant sound. The button syle overheat sender "pops" and makes contact, completeing the circuit, causing the alarm to sound, when it cools down it resets itself.

Thanks! I just want to make sure that I have the right sending unit. If you are standing behind the motor it would be on the port side near the top of the head. Mine only has a single wire coming from it which is tan in color. This is the wire that I ran to the sending terminal on the teleflex gauge. On the starboard side appears to be the overheat alarm which have 2 wires coming from it. This one on mine is for the heat alarm which does work.

What kind of temp gauge do I need? I guess the factory sending unit will remain but it does seem like the reading with the teleflex gauge is really high! Thanks.

 

[gss036]

Re: Operating temperature 1992 200 HP Mercury

I think you description is about the same, I looked at my OEM manual w/wiring schematic for the 1989's and it shows the same. Google the TelFlex site and go there, they have some great test sheets for guages, etc.
I had bought a new Merc sender for my motor, but as it turned out my guage was bad and I replaced it with a Telflex assy which included their sender, which was giving me the high readings.
The Merc sender looks like a condensor which was used w/points/condensor for older vehicles. The Telflex senders all press against the block/head assy and gives higher readings as they read metal temp;

 

[jdupree]

Re: Operating temperature 1992 200 HP Mercury

Update: First, thanks to all for the help.

Went out the other day without making any changes. The temp gauge is now reading between 160 and 170deg. The gauge could be correct because when I felt the tell tale it would not burn your hand but was very, very warm. Ran for about 1 hour and that is as high as it got. The water pump and impeller have been replaced. The only thing that I could figure is that the t-stats could be sticking and not opening when they should. I don't know the history of the t-stats but I think I might replace them. Could you tell me what temp they are rated at when they should open? Thanks again!

 

[Texasmark]

Re: Operating temperature 1992 200 HP Mercury

Son has a '95 150. Overtemp switch in each bank of cylinders; tan wire on port, tan/blu on starboard. Both go to a junction block where tan/blue goes off to the horn. The switch shorts to ground (case tied to head water jacket cover mechanically) when overtemp is reached. My service manual for a different engine says 195 degrees for the horn. Yours may be the same.

Pellet has 143 stamped on it which means it opens at 143 (give or take for tolerancing). Full open would be another 15 (more or less degrees). 160 for the engine working hard sounds fine to me.

Mark

 

[jdupree]

Re: Operating temperature 1992 200 HP Mercury

Thanks for the reply. That would make since because while running at WOT the temp actually drops down to around 130 to 140 and stays there. Then when you come off WOT and go to trolling speed it shows about 160 to 170deg. I guess this temp range is fine. Just want to make sure she is not running too hot. I might just pull the t-stats anyway and test them in the water and see what temp they open at. Thanks

 

[jdupree]

Re: Operating temperature 1992 200 HP Mercury

Son has a '95 150. Overtemp switch in each bank of cylinders; tan wire on port, tan/blu on starboard. Both go to a junction block where tan/blue goes off to the horn. The switch shorts to ground (case tied to head water jacket cover mechanically) when overtemp is reached. My service manual for a different engine says 195 degrees for the horn. Yours may be the same.

Pellet has 143 stamped on it which means it opens at 143 (give or take for tolerancing). Full open would be another 15 (more or less degrees). 160 for the engine working hard sounds fine to me.

Mark

Mark,

Still trying to figure this temp thing out. Took her out today and temp was a constant 160deg at WOT. Coming down after WOT she had increased to 180 to 185deg. I then felt the tale tale discharge and she was on the borderline of hot. Water pump appears to be pumping well because the discharge looks strong.

Just say the motor is running at 180deg. Would that be damaging the motor? Should I pull the t-stats and put them im warm water to see when they open? Thanks

 

[gss036]

Re: Operating temperature 1992 200 HP Mercury

I think it is time to consider changing the poppet valve. Not very expensive and easy to do. You need to take out the lower cowling screws and tap the cowling out of the rubber mounts and lower it enough to allow easy access to the starboard side of the engine. You might have to move a couple of wires out of the way. I would suspect you have the same setup as mine and the cover (figure 8 design) has 4 small 3/16-1/4 bolts to remove. Be carful you don't break or strip them out, you might have to tap (lightly) on them first and try some Blaster PB soaking overnight. White vinegar does a good job cleaning up the inside cover if you are running saltwater.

 

[Texasmark]

Re: Operating temperature 1992 200 HP Mercury

10-4 on the poppet because higher speeds is where it comes into play. The opening is much larger than stat openings and water pressure, either from ram injection, high impeller rpm's, or both force it open.

Mark

 

[jdupree]

Re: Operating temperature 1992 200 HP Mercury

It is funny that you guys mention the poppet valve. It was replaced right before I bought the boat. He gave me a receipt and the old poppet valve to show that it was done. The motor was checked out by a dealership in January right before I bought the boat. The dealer invoice said that water temp was good on the motor. I notice that it starts running hotter coming down from 4000 to 5000 rpm's.

I know the answer to this question, what if I pulled out the t-stats and gave it a go that way. That might damage the motor?

 

[gss036]

Re: Operating temperature 1992 200 HP Mercury

I don't think you will do any damage to the motor, it will just run cold and take longer to warm up. When the temp does come up, and when/if the poppet opens as it should you will see a drastic drop in the temp reading and the heads will probably be only slightly warm or maybe even cold if you have good circulation of the water.
I have heard of a lot of people removing the stats. At least you can give it a try to see if does make a difference and real simple to them back in.

 

[Texasmark]

Re: Operating temperature 1992 200 HP Mercury

I bought a used engine 18 mos ago and first time out discovered the stat stuck shut. Since engines ran without them for many 10's of years I thought what the heck and left it out.

In short, smarter now and the stat belongs.

On your V engine you have to have stats to get the starboard bank completely filled with water due to the offset in the block caused by the V design. I know that because I was flushing out the son's engine with the stats out, looking into the holes while idling on the muffs and learned what I said about water circulation.

So sir, "don't leave home without them".

Had a car with a stat that had been in there for a long time. Was having no problems with it. Figured it'd be good PM to put a new one in. Wrong. Next trip out was to go fishing and there I sat on the side of the road in the middle of nowhere with an overheated engine on my car. Bracket on new stat was defective and broke.

You be the judge on the previous work you mentioned.

Mark