Overheating 1987, 175 Mercury V6

[1933jim]

I have read all the various overheating problems on this forum and I am still confused. I have removed, cleaned and replaced gaskets in both heads and exhaust manifold. I have inspected and replaced the impeller in the pump and replaced the copper tube from the pump. The poppet valve diaphram was replaced and the new thermostats have been removed. All of the above and the engine runs very hot from1500 RPMs and up where the RPM must be reduced or the temperature will reach above 200DegF. Below 1500 RPM the temp is 160DegF. The temperature gauge was replaced along with the sender. The gauge was checked with an IR thermometer. Timing was checked also.

It appears to me that there must be a blockage someplace but I am lost as to where to begin looking.

 

[andy6374]

Re: Overheating 1987, 175 Mercury V6

Did you replace the waterpump?

Do you have a water pressure gauge? If so, what are the readings at various RPMs?

Did you replace every component of the pressure relief system and not just the diaphragm?

 

[KCLOST]

Re: Overheating 1987, 175 Mercury V6

The alarm will not sound until the head metal temp. reaches 245F. If you are not getting an alarm, you are ok.
210-220F readings at WOT are normal...

 

[gss036]

Re: Overheating 1987, 175 Mercury V6

Jim, when you replaced your temp sending unit and
guage, did you use Merc parts or TelFlex?
I went through this with my 89 200 and when I put a new Merc sending back on the engine, the temo dropped back into the previous range I had been accustomed to.
You do need those thermostats installed as they open at 143 degrees and allow the water to flow freely.
If you do not have a water pressure guage, get one as that will be the cheapest preventive maintence that you will do.
You obviously have water flow, then maybe you can induce a salt away solutition into the block some way and maybe get a salt blockage disolved it there is one?
Normally, as you increase RPM the poppet will open and allow excess water to circulate and make its' way through the exhaust. If you do a search there is a water flow chart available on this board, look at it and it will give you ideas where to look if there is a blockage.

 

[1933jim]

Re: Overheating 1987, 175 Mercury V6

Both the water pump and impeller are new. I only replaced the diaphram on the Poppet valve. No, I do not have a water pressure gauge. I will get one and install it before I go out again. I tried to check water passages today and removed the Poppet valve to check flow. When I ran a high water pressure through the engine I heard something come loose internally. Then the water seemed to run through the system freely. I installed the Poppet valve and ran pressered water through the system again and the poppet valve opened freely. Without a pressure gauge I have no idea how much pressure it took to open the valve.

I was told by Mercury that 240 deg temp. would be the end of this engine. I have water passing through the engine but the high temperture is what concers me. I don't think 200deg at 1800 RPM is OK

Thanks, I'll be back.

Jim

 

[Boston Habba]

Re: Overheating 1987, 175 Mercury V6

Jim, relax. I have the same engine and it runs in the red zone most of the time. I have had this engine for four years, run it at least twice a week. If there was any significant problem It would have shown up by now. My overheat alarm functions (tested it) but does not go off. If yours isn't beeping, you should be OK.

KCLOST and I discussed this a year+ ago and decided that if the alarm isn't going off you are OK.

Now if only this engine didn't gulp gas!

 

[gss036]

Re: Overheating 1987, 175 Mercury V6

The poppet will open at about 8 or 9 #, so you have water flowing, that is the main thing.
A water pressure guage is good insurance, that way you know the water pressure is there.