HOTTZU98

Where and how many temp sensors are there on a 1996 454 mag efi? I suspect I have a bad one. Ijust changed my theremostat and I get the same temp readings as before I changed a new 170* tstat in. It will run 150-170 when running on palne but at idle goest to 150*-145* any ideas? I recently swaped engines and with the old engine it read 150* within minutes now wont hit 150+ until on plane?

Outdrive1

I believe your sensor is up front by your thermostat. I know that you if you buy a sender with a different range than your gauge is set up for it will work but not correctly. Sounds to me like yours may not be reading the right temp but that it is working. You could just live with the wrong temp knowing what your motor normally operates at or you could try to replace it with the correct one to feel better about it. The factory part should be 806490t. If you give your serial number to an authorized dealer they should be able to get you the right part number for sure, that is unless who ever rigged your boat or owned your boat didn't change the sender to operate with a gauge that didn't have the same range as the factory sender was set up to operate at.

trivalleyboater

I just went through this on my 502s. You can search my thread "502 mpi" The temp sender is on the termostat housing on the left side. It will have a eyelet or a rubber slide on plug, not a clip in harness. If you could borrow a infa-red temp gun, that would tell you your engine temp for sure (point it at the front, top of the thermostat housing).

As the previous guy mentioned, you must replace the sender with the same resistance sender or the gauge will read wrong. We had problems with that. In my cousins boat, I tested it with the infa-red and the gauge was high by 25 degrees! So we installed about a 47 ohm resistor in the sender wire behind the gauge. Now, it reads pretty close, about 149 degrees ... infa-red showed about 145. Good Luck!

trivalleyboater

Before checking your engine as in my first post, are you sure you have a good / new impeller? That could be a sign that the impeller is wearing. It is somewhat common for a motor to run a little hotter under a load. Are you sure this is different? 170 degrees would be acceptable. What about the condition of the circulating pump. Are you getting good water flow? Once you have eliminated these items, get a hold of an infa-red and check out your actual water temp.