'93 Ski Nautique 351 PCM Pro Tech Overheating

Can't confirm anything what the original service tech did concerning stat replacement other than the 160F that I took out(it was installed correctly) which should have been a 143F. All I know is that when I replaced the 160F to the new one it seems to work like it should.

Will be replacing decals in the next couple weeks. One good thing about the whole process is how much I have learned about my boat. This is my first one.

Good to hear of your progress. Sometimes the cause is right in front of you, but mixed in with extraneous information.

Your boat looks great. Have you considered replacing the side graphics?

I ordered a new 143F from SKIDIM today along with several other items and spoke extensively with Vince(great help). He indeed said it probably was a faulty thermo, but still could be a number of other things. I couldn't wait so I drove to Houston to pick one up from Palmer Power. I spoke a good long while with the manager there who also was very helpful. I showed him the old thermostat that I took out and he confirmed that it was a 160F. Remember in my previous post that when I found out the tech had installed a 160F I had him change it back out to the original 143F which he said he did. Obviously he LIED.
Well I got back home and immediately installed the new thermostat. Hooked up the water supply and started the boat the temp. rose to 140-150-160 all the while I had my hand on the top of the thermostat housing to see if I could tell a temp. change. At 165 I started to feel a difference, at 170 it stopped rising and dropped back down to 160 and stayed there. I let it run there at about 1,000 rpm for about 5 minutes feeling spots on the engine, checking water flow out the back. I felt safe to rev to about 1,500 with not much change. I decided to install my fresh water strainer back inline, had to go to local auto parts store to obtain new o-ring. I installed the strainer along with reconfiguring my water hookup. I this time used a 5 gallon bucket to let the water hose fill the bucket and let the motor pull the water from the bucket. With the bucket full and water running over I started the engine. Same result with the temps and felt good suction from the hose connected to the engine. At 1,000 rpm and water on all the way, the bucket would still run over. At about 1,500 the bucket would stay level with the top, at 2,000 the water level in the bucket starts to drop fairly quickly. I feel pretty confident I have solved the issue, but the true test will be getting it into the river(hopefully tomorrow evening, have to work). Another step I want to verify is test the engine areas with thermo gun(hopefull tomorrow or Thursday). On and by the way I still have yet to recieve a call back from the shop where the original service was done(imagine that).

And the best way to test either one is to suspend it in the water.If it sits on the bottom you will get a false reading due to the contact to the hotter bottom of the container.

Something just doesn't sound right here. Two brand new stats of different temps and both bad?????? What are the chances of that?

I would confirm that the stats weren't installed upside down and when you get the new one put it in a pot of water on your stove and heat it up to verify that it does open at 143 before you install it.

I also posted this on planet nautique so I will give the same update here.

After having done nothing to the boat since my last post(working alot) and waiting on someone to help me I took it upon myself to pull it out of storage to my house. As noted in my previous post the Houston service tech said he changed the thermostat. I am a below average mechanic and am leary about messing with engines. I took a chance and hooked up a homeade water supply system to my boat to check temperatures myself. I bypassed the water strainer and verified that I was getting water through transmission cooler. Learned a lot about how to do all this on these forums(thanks guys). Without the boat running I was getting water out the rear exhaust. Feeling safe to start the engine I did and temp gradually started climbing till it got to close to 200F and this is where I shut it down. I did during that time rev it and water shot out of the rear exhaust. Going through the overheating steps at SKIDIM this told me that the water pump was good. I decided to pull the thermostat myself and leave it out and check temp again. Started engine and temp never rose above 115F. WOW. This does tell me that I am getting water through the jackets doesn't it? I did this several times with the same result. Called the shop where the service was done and just so happen the tech who performed the service had to step out. Talked to the owner about what I had found and he verified that from what it sounds like the thermo is bad. As noted in my previous post the tech suggested that I have a machine shop pull the engine and clear the water jackets. He quoted me a price from someone he new at aroung $3,500 for the whole job.
I will be ordering a new thermostat tomorrow or might even go to Houston(75miles away) and pick one up myself. I could understand that the orginal thermostat was bad but he installed a new one(or so he said) and when I found out he put a 160F in instead of original 143F I had him change it out. It still overheated after all this.

Hmmm, might have to pull the engine.   A nice slow-season job.      But that would be milking the customer . . .

Tim, I know it sounds kind of simple, but have you tightened all the hose clamps (with a nut driver) and made sure the raw water strainer is tight (and the gasket is in proper order)?
Got the same engine in my 93 Sport and it will do the same thing after multiple hot and cold cycles during the season. Tightening down everything brings it back down into the proper temp range.
I know the shop checked for hose clamps and cracked hoses....but did they actually tighten everything properly? I have worked in the boat business around a lot of technicians and sometimes they miss the obvious. Especially with the large punch list of things to go over.
Just sayin!

Time for a new marine shop. Verifying the proper, functioning thermostat should have been pretty high up the diagnosis list. Then again, posting accurate information helps too.

Bri892001 wrote: tsassman wrote: M3Fan wrote: That boat shouldn't have the 160 t-stat. A 160 T-stat will put your temp at around 180 or slightly above which may be what you are interpreting as an overheat situation. It should have a 140 t-stat. As stated at top all wires and connections were checked. I am planning on buying a IR gun to test it when I get the boat home this weekend. Thanks. I agree with M3Fan on the Thermostat. A 93 era boat would typically have a 140 (143 actually) T-Stat. If someone did actually retro-fit a GT-40 Fuel injected engine in this boat, it may then call for the 160.

You are correct. My mistake and I have edited my post. It is a PCM 351 Pro Tech. Thanks for the catch.

I just got off the phone with Karen( great help) at SKIDM.com(Discount Inboard Marine)and she informed me that they went to the 160F in '94. She says that I should have the technician put a new 143F back in, not that the 160F is bad just to help with the cooling issue. She also said that the typical running temperature for this boat is 180F -185F. Also, she said that 190 is typical. When is gets close to 200 is when you have problems.

M3Fan wrote: That boat shouldn't have the 160 t-stat. A 160 T-stat will put your temp at around 180 or slightly above which may be what you are interpreting as an overheat situation. It should have a 140 t-stat.

As stated at top all wires and connections were checked. I am planning on buying a IR gun to test it when I get the boat home this weekend. Thanks.

Some good advice so far.

Also, lets see some pics of the motor. Curious about a 93 Ski Nautique with a GT-40 engine.

you probably already checked this, is there blockage in the exhaust line that is not allowing water to flow freely? Chack passage from exhaust manifold to stern.

Thier reasoning for dismissing the circulating pump is backwards, and therefore the conclusion is suspect. Intermittant block temp, with a known good RWP, with good temp at both manifolds and risers would be a result of a bad circulation pump. Could also be rust mind you but I have seen some pretty cruddy blocks cool just fine, and a very fresh and clean one with a bad circ pump (loose impeller) cause the exact behavior you are experiencing -- eventually leading to a valve sticking, breaking, dropping.

That being said - as mentioned if an engine is running hot always always check your timing with a good light and make absolutely sure it is correct.

If I was really worried about rust with the water pump off I would pull the core plugs off the side and blow a bunch of compressed air everywhere i could reach and see how much comes out.