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OK this is strange

8

88_grady_white

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"I have an 87 Merc 175hp that

"I have an 87 Merc 175hp that runs great (still). That's not the strange part.
I have been dealing with a heat issue in this motor that is driving me nuts. From just off idle to about 3000 RPm's it runs hot (very hot) and it never used to. This would lead me to believe that the poppet valve is not functioning correctly.

Before you start thinking, new in the motor;
Water pump(s) (pulled a couple of times to make sure everything was correct, and it definately is)
Thermostats
Poppet valve
New old stock heads (very clean)
Power packs and stator
All water passages checked to ensure propper flow
Water pisses out of the telltale like me when I was 20!

Any other suggestions on this would be appreciated!

Here is the strange part (finally). The poppet valve does not appear to have anywhere to dump the extra water? What I mean is, the newer models have another passage next to the poppet plate where the water diverts to, this one just has a plug valve held in place by the spring and plate - when the poppet lifts where the hell is the water supposed to go? I do have a sand plug in the motor that I could pop out and install the newer type poppet setup (after drilling and tapping a couple holes around this passage). But as I said before, the first six years I owned this motor it ran in the cold no matter what. GO FIGURE."
 
Maybe the exhaust gaskets are

Maybe the exhaust gaskets are leaking or the plate is letting exhaust get into the cooling system.
 
"Tony,
Very interesting, neve

"Tony,
Very interesting, never even thought of that since I've never broken this motor down that far. I'm not even really sure where the exhaust plate is on this thing or how far I would have to disassemble in order to replace. I didn't think the water jackets even ran close to the exhaust on these engines??

Thanks for the insight.
D"
 
"OK, so I did a little researc

"OK, so I did a little research and find that the plate between the heads is what houses the exhaust plate and the rest. Would anyone happen to know if this plate can come off without removing the heads? (of course the coil packs would need to come off and a few miscilanious do-dad's but that's simple enough)

This definately makes sense since I notice what appears to be steam coming from the two exhaust holes under the tell-tale. Compression test says that the head gaskets are good (after all they are new).

Thanks!"
 
"Thanks Graham,
Does this sou

"Thanks Graham,
Does this sound to you like something viable that may cause an overheat issue? Top speed the engine cools off but seems to be getting a bit worse as the summer goes on. I've pretty much checked everything else but seemed to have overlooked this."
 
"Yes, gaskets are always suspe

"Yes, gaskets are always suspect - exhaust or powerhead base (especially if accompanied by an occasional "cough" or "sneeze") can cause your symptoms."
 
"WTF? How could the water not

"WTF? How could the water not have anywhere to go? Makes no sense at all. Either the valve did not open or there is a blockage. If you have 20 PSI of pressure. This has nothing to do with the exhaust plate. The water comes through the plug hole and dumps into that pocket, than out the bottom. "
 
"Some of these valves had a 4

"Some of these valves had a 4 bolt cover with a bypass hose running to the top. Others did not. Which one do you have? If somebody switched it, you will have problems. Bad P/H gaskets cause issues as well."
 
It's obviously going somew

It's obviously going somewhere - maybe right down the exhaust housing through a bad base gasket before it can get up to the top of the head
 
"I am having the same problem

"I am having the same problem with 1991, 150 blk max, temp at idle is around 160, and temp between 25mph - 60mph is 200, but temp from 10-20mph will reach 240 after about 10min."
 
"Bandit; I have the 2 bolt sty

"Bandit; I have the 2 bolt style and this has not been changed for the 10 years I've owned it. Of course the poppet was changed but not the style and I'm the only one who touches it.
It all kind of started back when I lost a stator, a power pack, and a head all in one week (talk about a bad week) The stator and the power pack where definately related and went at the same time, the head gasket appeared to have been leaking a small amount of water into the cylinder and from the water flashing off to steam it actually put a nice big pocket in the head. Don't know if this is related to the heat issue at all but figured I would throw it out there.

Ronnie; I've heard this problem a couple of times with these motors (87-88) in particular and never really got an explaination from anyone, but I will be sure to post what I find!! AND I WILL FIND IT!!! Unfortunatley I don't have nearly enough time to do a complete tare-down these days.

D"
 
One last post on this and I&#3

One last post on this and I'll leave it alone.

I was wondering if overheating the engine when I had the head problem would cause an exhaust gasket problem??
 
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