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Hey guys, I lost the impeller a few months ago and had to pull bits of rubber from my engine. The boat never got hotter than 160. I replaced the impeller and cleaned the entire cooling system. I decided to install a new thermostat (140), temp gauge and sending unit while I had it apart. Today was my third trip after the repair and my boat never gets above 125 on the gauge. The engine runs great and seems cool enough. When idling, the hose pressure from the raw water pump seems low. Should the temp go to 140 or is 125 o.k.? 1989 malibu skier 5.7 350. Any advice would be helpful, Thanks

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I'm going to throw out the possible obvious, but what temp thermostat did you buy? They sell them with different settings. I don't mean to insult, just throwing it out there.

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Temp should go to 140. You need to verify what is not working correctly. An infa-red thermometer is a nice tool to have right now. I think they had trouble keeping the exhaust manifold below 200 degrees back then in '89, hence the 140 stat instead of todays 160 stats. Your engine will run better at 160 but the important factor (NMMA and Coast Guard regulations) is keeping the surface of the exhaust under 200 degrees.

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mine does this too, let me know if you find out why, I've replaced the temp sensor and the thermostat, even tried the higher 160 degree one but she still stays at 125 most of the time.

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here is kind of an oddball suggestion based on the idea that the gage is suffering from some kind of inaccuracy.

any of your buddies have a boat with the same block?

if so; consider observing their engine temp. gage and noting the temperature.

then swap out sending units, that is an easy task.

run yours up to temp and compare the temps.

that should give you some baseline from which to sort out the next step.

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  • 3 weeks later...

Sorry for not posting sooner guys but I have some info that may help out. I found out that the previous owner installed the thermostat gaskets the wrong way. The lower gasket must have the brass contacts on it. If these contacts are not touching the intake manifold and the thermostat housing the sending unit will not be properly grounded. I removed all the gaskets and cleaned all surfaces and scraped the manifold to ensure a clean contact. I also did not use and silicone sealer on any parts. Temp gauge worked great. Hope this helps.

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  • 3 years later...

Your engine will run better at 160 but the important factor (NMMA and Coast Guard regulations) is keeping the surface of the exhaust under 200 degrees.

I'm just curious...I can't find any regulation regarding this. The only reference I find is that raw water cooling should be limited to below 145 degrees due to salt being more corrosive at those temps. I've always wondered why fresh water motors aren't running higher temps.

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