Guys, I have a 99 353 with 502 Mags ( MPI). My port motor was out winter before last to replace a coupler and since then I have struggled with water temps that get just high enough to trip th ewarning lights on my original Gaffrig temp gauges. The temps normally run around 170 on the gauges, but if I get on it for more than a few minutes they creep to 180 or slightly above and the light comes on. Prior to engine removal this did not ever occur. I've asked the dealer to check the ground strap, thinking it may be the culprit and have been told it is fine.

I also noticed this weekend that the left side ( facing motors) risers on both engines are hot to the touch ( can put a hand on them, but not for long) compared to cool on the right side risers. Is this normal? We've used a Snap On thermal gun to check temps at WOT and temps were under 180 at risers and the thermostat housing. Thoughts? Boat is 100% fresh water its whole life. Running 160degree stats. Thanks

My thoughts are . . . check the oil cooler for clogs on the engine that is running hot.

Typically one side of the cooling system gets 'favored' by the flow of cool water to the risers. this will reflect in a difference in the elbow temperature. They are probably OK, but you could 'twaek' the flow a bit on the cool side to force more water to the side that is running hotter.

I'll almost guarantee whoever did the coupler R&R crushed the hose going to the pump or the hose coming out of the pump that goes to the cooler when they reinstalled the motor. Did you shoot the risers and thermostat housings on both motors and compare? Until you are able to provide some more info comparing one engine to the other I'd check the hoses I mentioned. I think that's where you'll find your problem. Also, If that's not the problem you should post this in the general section of the forum. You'll get a lot more response from some very knowledgeable members.

Thanks for the replies. To clarify, both motors are running the same temp at the gauge and both have left (actually stbd) side risers that are hot to the touch. I will check the oil cooler hoses for blockage and or kinks. Not sure if these motors have popet balls or not, but will check that too. I ordered new gauges without the warning lights ( all you can get now anyway), but one was defective. Pain in the butt. Flow from the thunder box is good as well. Thanks

My 350 mag had one hot riser and I found rubber chunks from an old impeller lodged in the small outlet where the plastic ball is in the thermostat housing.

The odds of that happening on twin engines on the same side would have to be astronomical but it is easy to check so I'd make sure the thermostat housing is all clear.

Good project for Saturday am. Thanks for the help.

When you find out what's going on please post. It might help someone down the road.

Ran the boat last weekend and took some temps using an infrared temp gun. At 3500 RPM steady, the port risers read about 100 degrees, stbd read 135. Thermostat housing was at 135 on both motors. Identical results on both motors. Gauges are reading approx. 170-175 on both motors at the time of the readings. Water flow appears to be great. I ran the boat at WOT and the temps on both motors rose ( on the gauges) to 180 and red warning lights came on. They continued to slowly climb , so I backed down to 3500 RPM and temps immediately dropped to the 170 level or less. Make any sense? I'm wondering if a bad battery might contribute to funny readings? I know one is weak and that trim on the stbd motor doesn' t work well when the battery is on Number 1. Buddy of mine had other electrical gremlins that were resolved with new batteries. Just a thought. Thanks , Steve

I am now wondering about a ground problem that may exist that contributes to the sending unit reading too high. Is that possible? Would a bad or imperfect ground create such a problem at high RPMs? I do know that the water temp gauge sending units are very sensitive to ground and just don't know if a bad ground would give a high or a low reading. I am also experiencing an occasional Tach RPM difference of about 300 to 400 RPMs between the two tachs. Problem is, the errant tach ( ie, the one that fluctuates) is the motor that was not removed for teh coupler. Last question, where would I find the main ground strap for the motors? I'd like to make sure those are clean and tight. Thanks!

I have the same experience with my 7.4 mpi. The Starboard side is a little warmer than the port. I have spoken to a number of mechanics and they all same the same thing a tpenfield - one side will always be warmer and you will drive yourself crazy trying to figure out why.

my 2 cents

Safe Boating

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