500 EFI Running hot
 

I just bought this boat with about 200 hours on it. Impeller was replaced before i bought it and i just put a thermostat in. Normally runs between 150-180 but sometimes will hit 220! I am planning on replacing impeller and backflushing the lines. Any other suggestions?

Drill three or four 1/8" holes in the stat.

It should run between 160 and 180* all the time. It definately should not get to 220*. At 200* or so, the alarm should be going off. If its not, then its a bad gauge.

If your boat is equipped with sea strainers, have a look at them to make sure they are not clogged

Also look to see if the circ water pump is leaking or not, That would make it run hot. Do you think the warning horn is working? it should beep at key up to let you know it works some times.

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.

When people talk about overheating and can't find the cause, I wonder
why no one ever mentions cleaning out the oil cooler? In fact, cleaning
out the seawater section of the oil cooler is shown as a yearly maintenance item in my 575SCi owners manual (it's the same cooler that is used on the 500EFI). You have to take them off and rod out the water section. Get all
the little tiny stones and various clogs out.

Several times over the years I've sucked sufficient sand to clog them enough to have high temps. And these are stone sizes that can make it
past many sea strainers.

Pesky Varmint

The oil cooler is moounted on the back of the engine right? Looks like it will be fun getting it off, having to work around the sport tubes and all

you can remove the end caps ( one bolt on either end ) and use compressed air to blow out any debris in the cooler.

Sweet. Thnx every1 for the help!

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.

Do a compression check. A blown head gasket will increase your temps.

If the alarm is not going off past 200* then I would bet on a gauge or sender acting up.

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!!!

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 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.

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:eek: Just my 02 worth, Good luck with it.

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.

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.

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.

Pick up a Laser Temp Gun and carry it with you whenever towing or boating. Use it to find bad bearings, brakes, tires (will be hotter than the rest) when towing, and use it when boating to validate your gauges and also find hot cylinders if you have trouble. Priceless investment.

what temp should a 500efi run at? mine is running around 150ish ,no higher

Well now mine is usually at 160 but sometimes will hit 180 and then it seems the thermostat opens up and rapidly drops down back to 150. I have a laser thermometer and will def compare it to my gauges thnx. Good idea!

Your fine, You should be running a 140 degree thermostat and a lot of times the gauge will show 10-15 degrees more then what the thermostat degrees is.