Engine/Transmission (1994 - 1998) Grid Heater Working right??

[drees1]

My grid heater seems to work ok and cycle when cold. But it will always cycle any time I start the truck when it is below 60 deg F. , ambient. Even if the truck is warm and just turned off. As long as it is below 60 deg F. outside it cycles. Is this correct?? It seems to me there should be a coolant sensor to over ride it when the engine is hot. If that's true, how do I fix it?? Thanks for any help.



Doug Rees

 

[illflem]

The sensor for the grids only measures intake air temp but 60° is too warm for the heaters to come on, it should be below 50°. Even if the engine is warmed intake air may be below 50 but only when the temps are really cold. Your sensor or it's wiring may need attention.

 

[Missouri Mule]

illflem's right (kind of) grid heaters do measure air temp coming in to intake manifold.

There is also a pre and post cycle post cycle should turn off on most years of 12 valves around 15 mph or as I recall 5 minutes ( I have to check that one out).



But I disagree with the under 50 degree temp, (I will check this out also).

From the 96 service manual (from memory) it states at or under 59 degrees the grid heaters will be activated.



If it gets down to 59 right at sunrise or a little before the air in the intake may not be 59 (and usually isn't) so the wait to start light will not be activated.



drees1, seems like your system is working fine.

The only "if" I can see is if your grid heaters remain on for an extended period of time like 15 to 30 minutes(cycling) or 30 miles of driving.

 

[JohnE]

The IAT sensor signal is read by the PCM. The grid heater relays are controlled by the PCM.

I don't know the PCM logic for timing cycles and over rides such vehicle speed or coolant temp.

 

[illflem]

MM is right, the temp for the grids is 59°. According to the manual the PCM will only allow the grids to cycle for three minutes max after starting, the time depends on the intake temp only. They will also not cycle if you go faster than 17 mph.

 

[drees1]

Thanks for the responses. It sounds like it is working ok. I might put in a manual switch to turn it off when coolant temp is warm, but cold outside. The engine certainly does not need assistance when it is warmed up.



Doug Rees