Overheating Stingray 556ZP

Hi All my name is Mike, I have been enjoying reading these forums,I am not new to boating but I just bought my first boat in 20 years. It is a 1993 Stingray 556Zp with Stock 3.0L engine. Today a friend of mine and I put it in the water for it's maiden voyage. All went well until we could open her up and she started to over heat. I could run at low speed all day long at about 150-160 degrees. At speed the temp gauge would start to climb to an uncomfortable 200+ and the engine would not cool down until I shut it off. Then I could restart and run at low speed all day again. When I got home connected the hose and ran it up to temp again and I notice the outlet hose going to the exhaust was staying cool while the big hose going to the engines water pump was hot. The temp gauge was reading 140+ thermostat should be open and hot engine water flowing through the outlet hose. I removed the thermostat and it ran on muffs again this time temp there was no temp on the gauge and all the hose were the same temp (by touch). My previous experience has been with an 1980 4 cylinder Merc 50, this is my first Mercruiser. (not a good start LOL) I am thinking the thermostat?? Unfortunately It will run on muffs with out overheating and I am running out of days here in NJ to test on the water. Any advise is greatly appreciated. Sorry if I seem a bit long winded in my first post but I am trying to give as much detail as possible to diagnose this problem. Looking forward to a fun summer on the New Jersey coast in 2011.

Mike

PS I have been reading the restoration forum recently and you guys do awesome work. I am totally blown away.

Re: Overheating Stingray 556ZP

Ayuh,... Welcome Aboard,...

Drop the lower unit,+ rebuild the impeller pump...
Then put the t-stat(New 1, of course) back in, 'n Go Boatin'...

Re: Overheating Stingray 556ZP

Forgot to mention the previous owner told me he just replaced the pump in the drive and the gear oil. He could have messed it up but it seems to have plenty of water flow.

Re: Overheating Stingray 556ZP

but it seems to have plenty of water flow.

Click to expand...

How would you know that?

The previous owner could have "messed up" or he just said he did the job and didn't...or a previous impeller failure has sent impeller fragments into the t'stat housing and is plugging it, or your exhaust elbow or manifold is plugged with rust.....

There's a common thread........ Engine overheating is fully related to total cooling water flow through the engine and exhaust system from the raw water pump all the way from the pump to the exhaust.....


Cheers,


Rick

Re: Overheating Stingray 556ZP

I ordered a Tstat, tstat gasket and both end plate gaskets, once they arrive am going to install the Tstat and start cleaning out the manfold and other related exhaust plumbing. Then will put back it the water and try again. Hopefully this season before I winterize. Then will start looking into the raw water pump. It an Alpha 1 Gen 2 drive I believe the drive lube needs to drained and refilled when doing the pump. I get to by Tools . Anybody know a good Mercruiser parts dealer in central NJ