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500 EFI Running hot

500 EFI Running hot

Old 06-07-2009, 12:37 PM
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don't drill the stat as suggested. the efi has its own bypass and if you make the stat not work as designed the lack of proper temp at the sensor will make the efi think it needs to be richer than it needs to be. you'll screw up the fuel curve for no reason. assume the system worked fine as designed ( it did) and find the REAL problem and fix that.
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Old 06-07-2009, 01:01 PM
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Do a compression check. A blown head gasket will increase your temps.
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Old 06-07-2009, 02:01 PM
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Originally Posted by WarlockCat 28 View Post
The alarm is def not going off. I will check to see if it beeps with the key. The boat does not have a strainer so im afraid i sucked up something.

If the alarm is not going off past 200* then I would bet on a gauge or sender acting up.
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Old 06-07-2009, 02:57 PM
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Yea def not gonna drill holes in the stat! The alarm doesnt go off after 200. So is the alarm hooked in with the temp sensor and not the gauge? I just put a new stat and i used adhesive to hold the gasket to the housing, Im wondering if that could be messing up the grounding tabs on the gasket. I sure hope its not a head gasket!!!
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Old 06-07-2009, 03:33 PM
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Originally Posted by WarlockCat 28 View Post
I just put a new stat and I used adhesive to hold the gasket to the housing, Im wondering if that could be messing up the grounding tabs on the gasket.
Water Temperature Ohms Reading
140 F (60 C) 121-147
194 F (90 C) 47-55
212 F (100 C) 36-41


Oh.....and my stat is drilled on my 502MPI

Last edited by MacGyver; 06-07-2009 at 04:23 PM.
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Old 06-07-2009, 06:45 PM
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Originally Posted by WarlockCat 28 View Post
Yea def not gonna drill holes in the stat! The alarm doesnt go off after 200. So is the alarm hooked in with the temp sensor and not the gauge? I just put a new stat and i used adhesive to hold the gasket to the housing, Im wondering if that could be messing up the grounding tabs on the gasket. I sure hope its not a head gasket!!!
If you thermostat housing has any kind of sensor mounted to it then yes the adhesive is more then likely messing up the grounding to the sensor and giving you that kind of reading, You will have one sensors to read the gauge and one temp switch to tell the warning horn to sound any thing over around 200 degress, some times they are both on the T/ housing and some times one is in the intake manifold by the T/ housing. You should clean the housing and the intake and put it on dry.

Last edited by Boat Tech; 06-07-2009 at 06:48 PM.
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Old 06-07-2009, 06:54 PM
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Originally Posted by MacGyver View Post
Water Temperature Ohms Reading
140 F (60 C) 121-147
194 F (90 C) 47-55
212 F (100 C) 36-41


Oh.....and my stat is drilled on my 502MPI
If your engine is stock then you are wasting fuel and running rich and fouling your spark plugs and loosing engine performance by drilling it out one EFI engines Just my 02 worth, Good luck with it.
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Old 06-07-2009, 07:52 PM
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Originally Posted by MacGyver View Post
Water Temperature Ohms Reading
140 F (60 C) 121-147
194 F (90 C) 47-55
212 F (100 C) 36-41


Oh.....and my stat is drilled on my 502MPI
well. you're wrong. and it really is as simple as that. if you want the fuel curve to be correct, put an undrilled one back in. if you want the fuel curve to be worse than original (already a bit on the fat side) and use more fuel and make less power, then leave the drilled one in.
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Old 06-08-2009, 01:44 AM
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Back to the original problem.......................

The adhesive on the gasket is more than likely causing the problem. The crush rivets need to make good contact to ground the sender.

The alarm temp sender and gauge temp sender are totally separate.

As far as the holes in the tstat, they really should not be needed. If the engine gets to temp fine, then they are not hurting anything and will help eliminate steam pockets.
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Old 06-09-2009, 08:32 AM
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Replaced impeller and housing, and cleaned out oil cooler. Took the boat out and it wouldnt go over 190. So i think ive got it for now. I think my gauge is off a little becuase i have a 140 stat in it but it seems not to open up till 180 if i trust the gauge and not sure i do.
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