Fluctuating temperature gauge, erratic
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1st Gear
Joined: Jun 2022
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Fluctuating temperature gauge, erratic
I have a rebuilt 302 5.0L from 1987. I have digital gauges. Driving down the road 40+ mph
(90-95F outside and humid) my temp barely hits 190F°. If after 20 min of driving I have to stop at red light, the temp starts going up fairly quickly(one red light and it probably hits 200-205F). I have a new pusher fan 3000 cfm and new aluminum radiator. Once I can drive over 40ph for about 5 minutes the temp starts dropping again, amd becomes steady. if I stay in traffic, stop and go, temp starts quickly hitting 220 or even higher.
I find the temperatures kind of erratic at times during stop and go, quickly going up or down. Is it gauge issue, air in radiator or thermostat not working properly? I heard digital gauges are not that precise or constant
tnx
(90-95F outside and humid) my temp barely hits 190F°. If after 20 min of driving I have to stop at red light, the temp starts going up fairly quickly(one red light and it probably hits 200-205F). I have a new pusher fan 3000 cfm and new aluminum radiator. Once I can drive over 40ph for about 5 minutes the temp starts dropping again, amd becomes steady. if I stay in traffic, stop and go, temp starts quickly hitting 220 or even higher.
I find the temperatures kind of erratic at times during stop and go, quickly going up or down. Is it gauge issue, air in radiator or thermostat not working properly? I heard digital gauges are not that precise or constant
tnx
Cargo Master
Joined: Jan 2004
Posts: 3,118
Likes: 149
From: South Dakota
I would say the problem is with your pusher fan as you call it. It is not getting the air through the radiator properly when it needs to when you are stopped or moving slow. You don't need anything to push or pull air through the radiator at 40 plus MPH except in rare conditions. In my opinion there is nothing better than the stock design cooling system if it is working properly.
Lead Driver
Joined: Jun 2021
Posts: 5,221
Likes: 805
I have a rebuilt 302 5.0L from 1987. I have digital gauges. Driving down the road 40+ mph
(90-95F outside and humid) my temp barely hits 190F°. If after 20 min of driving I have to stop at red light, the temp starts going up fairly quickly(one red light and it probably hits 200-205F). I have a new pusher fan 3000 cfm and new aluminum radiator. Once I can drive over 40ph for about 5 minutes the temp starts dropping again, amd becomes steady. if I stay in traffic, stop and go, temp starts quickly hitting 220 or even higher.
I find the temperatures kind of erratic at times during stop and go, quickly going up or down. Is it gauge issue, air in radiator or thermostat not working properly? I heard digital gauges are not that precise or constant
tnx
(90-95F outside and humid) my temp barely hits 190F°. If after 20 min of driving I have to stop at red light, the temp starts going up fairly quickly(one red light and it probably hits 200-205F). I have a new pusher fan 3000 cfm and new aluminum radiator. Once I can drive over 40ph for about 5 minutes the temp starts dropping again, amd becomes steady. if I stay in traffic, stop and go, temp starts quickly hitting 220 or even higher.
I find the temperatures kind of erratic at times during stop and go, quickly going up or down. Is it gauge issue, air in radiator or thermostat not working properly? I heard digital gauges are not that precise or constant
tnx
Laughing Gas
Joined: Jan 2012
Posts: 1,106
Likes: 25
Your radiator is to big, your over cooling your system, it wont reach operating temp and or wont stay there long enough for the thermostat to stay open and that's why it keep fluctuating.
So run a single core radiator and get a good fan controller, I recommend autocoolguy, he makes some nice fan controllers.
I know this because I had the same issue with my 302, I had a auto part store 2 row radiator and a different fan controller, and did just about everything to keep my gauge from fluctuating, it finally stopped once I put in a single row rad and used autocoolguy fan controller set for a higher temp, which allowed my thermostat to stay open and operate properly.
So run a single core radiator and get a good fan controller, I recommend autocoolguy, he makes some nice fan controllers.
I know this because I had the same issue with my 302, I had a auto part store 2 row radiator and a different fan controller, and did just about everything to keep my gauge from fluctuating, it finally stopped once I put in a single row rad and used autocoolguy fan controller set for a higher temp, which allowed my thermostat to stay open and operate properly.
Lead Driver
Joined: Jun 2021
Posts: 5,221
Likes: 805
Your radiator is to big, your over cooling your system, it wont reach operating temp and or wont stay there long enough for the thermostat to stay open and that's why it keep fluctuating.
So run a single core radiator and get a good fan controller, I recommend autocoolguy, he makes some nice fan controllers.
I know this because I had the same issue with my 302, I had a auto part store 2 row radiator and a different fan controller, and did just about everything to keep my gauge from fluctuating, it finally stopped once I put in a single row rad and used autocoolguy fan controller set for a higher temp, which allowed my thermostat to stay open and operate properly.
So run a single core radiator and get a good fan controller, I recommend autocoolguy, he makes some nice fan controllers.
I know this because I had the same issue with my 302, I had a auto part store 2 row radiator and a different fan controller, and did just about everything to keep my gauge from fluctuating, it finally stopped once I put in a single row rad and used autocoolguy fan controller set for a higher temp, which allowed my thermostat to stay open and operate properly.
5) fan depth(if fixed on engine fan) 6) Cooling hose having spring on bottom 6) thermostat quality 7) temperature gauge on dash is read by a sensor while engine temperature for PCM Is different 8) the stock coolant gauge for me is about 25 degrees between N and L on Normal which is very misleading but its just how mine is 9) air bled??? 10) water pump,hoses, restrictors, bypasses, etc kept in check or used where needed
Laughing Gas
Joined: Jan 2012
Posts: 1,106
Likes: 25
With mine I found with a electric fan and a 2 row radiator it would heat up the coolant to open the thermostat but would over cool the coolant causing the thermostat to open and close constantly which shows on the gauge has major fluctuation sweeps.
Lead Driver
Joined: Jun 2021
Posts: 5,221
Likes: 805
Idk about your engine but at least on4.9 the placement of the sender for gauge is strategic as to be less pronounced like that
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