Red engine light
Thread Starter
Junior Member
Joined: Jul 2024
Posts: 25
Likes: 3
From: Michigan
Red engine light
Overheated my truck the other day and since then the red engine light will come on when the temperature gage reaches the N, once in awhile the temp gage will reach O without the red engine light coming on It didn't do this before it overheated.
could it be a bad sensor? Which one? The coolant temperature sensor? I did get a code for the air flow temperature sensor. I replaced that but still same results. What sensors determine the red engine light?
could it be a bad sensor? Which one? The coolant temperature sensor? I did get a code for the air flow temperature sensor. I replaced that but still same results. What sensors determine the red engine light?
Senior Member
Joined: Oct 2016
Posts: 3,700
Likes: 766
From: Parts Unknown
The sensor you changed tells the computer the temperature of the incoming air not the coolant.
There will be a coolant temperature sensor if you have a gauge or a sender for an idiot light screwed into the water jacket. It should be a single wire sensor. (not the one for the computer which probably has two wires attached) . But without knowing what you have and what year, who knows.The engine technically doesn't overheat unless the coolant boils over.My gauge typically runs at the "R or M" which doesn't really mean anything since the gauges cannot be relied on.
There will be a coolant temperature sensor if you have a gauge or a sender for an idiot light screwed into the water jacket. It should be a single wire sensor. (not the one for the computer which probably has two wires attached) . But without knowing what you have and what year, who knows.The engine technically doesn't overheat unless the coolant boils over.My gauge typically runs at the "R or M" which doesn't really mean anything since the gauges cannot be relied on.
Last edited by raski; Jun 2, 2025 at 03:07 AM.
Senior Member
Joined: Apr 2023
Posts: 4,294
Likes: 1,389
From: Near Salt Lake City
It is probably coming on due to low oil pressure as it warms up
Check the "actual" oil pressure with a "direct pressure gauge" screwed into the sender port
The light comes on at around 5 psi
* There is a resistor to fix the low reading ones that show good oil pressure on a manual gauge, but read low through a new sender
Check the "actual" oil pressure with a "direct pressure gauge" screwed into the sender port
The light comes on at around 5 psi
* There is a resistor to fix the low reading ones that show good oil pressure on a manual gauge, but read low through a new sender
Thread Starter
Junior Member
Joined: Jul 2024
Posts: 25
Likes: 3
From: Michigan
The sensor you changed tells the computer the temperature of the incoming air not the coolant.
There will be a coolant temperature sensor if you have a gauge or a sender for an idiot light screwed into the water jacket. It should be a single wire sensor. (not the one for the computer which probably has two wires attached) . But without knowing what you have and what year, who knows.The engine technically doesn't overheat unless the coolant boils over.My gauge typically runs at the "R or M" which doesn't really mean anything since the gauges cannot be relied on.
There will be a coolant temperature sensor if you have a gauge or a sender for an idiot light screwed into the water jacket. It should be a single wire sensor. (not the one for the computer which probably has two wires attached) . But without knowing what you have and what year, who knows.The engine technically doesn't overheat unless the coolant boils over.My gauge typically runs at the "R or M" which doesn't really mean anything since the gauges cannot be relied on.
Thread Starter
Junior Member
Joined: Jul 2024
Posts: 25
Likes: 3
From: Michigan
I forgot to add that the red engine light goes out when the temp drops below the N. It's an 89 f150 4.9l. Also the check engine light comes on when it's warmed up a bit but it clears every time the truck is shut off. I'm not able to get the code using the flashes of the check engine light while running. That only works when the truck is off.