pizzaman09 Posted April 13, 2023 Share Posted April 13, 2023 Now that warmer weather is here, I have found that my Comanche likes to overheat when idling. 1990 4.0L Renix with an all original closed cooling system. Has about a 1 year old water pump. I changed the harmonic balancer yesterday thinking it may be slipping and not driving the pulley but that wasn't it. It cools back down if I rev it up to about 2000 rpm and even better once I get moving. A couple days ago it got up to 235 deg F according to the REM and started to steam a little from an expansion tank fitting. Any thoughts on where to start? Link to comment Share on other sites More sharing options...
PIKE Posted April 14, 2023 Share Posted April 14, 2023 Fan Clutch Link to comment Share on other sites More sharing options...
jdog Posted April 14, 2023 Share Posted April 14, 2023 How's the shroud Link to comment Share on other sites More sharing options...
pizzaman09 Posted April 14, 2023 Author Share Posted April 14, 2023 2 hours ago, PIKE said: Fan Clutch I'll have to check that out. 2 hours ago, jdog said: How's the shroud Excellent shape Link to comment Share on other sites More sharing options...
cruiser54 Posted April 14, 2023 Share Posted April 14, 2023 Describe "overheats". Link to comment Share on other sites More sharing options...
gogmorgo Posted April 14, 2023 Share Posted April 14, 2023 Fan clutch is easy enough to test out. When the engine is cold (and off) you should be able to spin the fan by hand. When its hot, shut the engine off and it should be difficult if not impossible to turn by hand. Link to comment Share on other sites More sharing options...
pizzaman09 Posted April 15, 2023 Author Share Posted April 15, 2023 23 hours ago, cruiser54 said: Describe "overheats". About 10 minutes of idling it just keeps getting hotter until steam starts to come out at the weakest point which appears to be the upper return line of the expansion tank. Turning on the AC to kick the electric fan on seems to help. I did find yesterday that it was about 1/2 gallon low on coolant, I've topped it off and it is behaving better but I'm not convinced the problem has gone away. I haven't had a reason to let it idle for long. Link to comment Share on other sites More sharing options...
87MJTIM Posted April 15, 2023 Share Posted April 15, 2023 Is the e-fan temp switch bad? You say the e-fan come on with the AC, but it doesn’t when the temperature rises. Link to comment Share on other sites More sharing options...
cruiser54 Posted April 15, 2023 Share Posted April 15, 2023 Does the electric fan come on during this "overheat" time without activating it with the AC? Still have the coolant bottle on the passenger side firewall? Have you performed gogmorgo's suggested test on the clutch fan? Do you have a temp gauge or just a warning lamp? Link to comment Share on other sites More sharing options...
87MJTIM Posted April 15, 2023 Share Posted April 15, 2023 Just now, cruiser54 said: Does the electric fan come on during this "overheat" time without activating it with the AC? Still have the coolant bottle on the passenger side firewall? Have you performed gogmorgo's suggested test on the clutch fan? Do you have a temp gauge or just a warning lamp? I beat you to it! Link to comment Share on other sites More sharing options...
cruiser54 Posted April 15, 2023 Share Posted April 15, 2023 I saw that after I posted. LOL. I've only ingested 20% of a mug of coffee. Link to comment Share on other sites More sharing options...
pizzaman09 Posted April 15, 2023 Author Share Posted April 15, 2023 10 minutes ago, cruiser54 said: Does the electric fan come on during this "overheat" time without activating it with the AC? Still have the coolant bottle on the passenger side firewall? Have you performed gogmorgo's suggested test on the clutch fan? Do you have a temp gauge or just a warning lamp? I am going to test the fan clutch today, it is free when cold. The coolant bottle on the passenger side fire wall is original, I tried two replacements last year and both had pinhole leaks. I have both a temp gauge and a Renix Engine Monitor. The REM confirmed that it was very hot, 235 def F. In the winter it had no issues controlling temperature at the thermostat set point, just now that it up into the 60s to 70s out. I did confirm last year when checking all the sensors that the coolant temp sensor output is correct according to the factory charts for resistance vs temp. 11 minutes ago, 87MJTIM said: Is the e-fan temp switch bad? You say the e-fan come on with the AC, but it doesn’t when the temperature rises. I have not witnessed the e-fan kick on without also the AC compressor kicking on. Link to comment Share on other sites More sharing options...
cruiser54 Posted April 15, 2023 Share Posted April 15, 2023 Coolant sensor and Fan switch are 2 different things. SENSOR mounts on driver side engine block and sends input to the ECM. Fan SWITCH is located low on the driver's side radiator. SENDER is located at the driver side rear of the head and sends signals to dash gauge. Link to comment Share on other sites More sharing options...
rokinn Posted April 15, 2023 Share Posted April 15, 2023 4 hours ago, pizzaman09 said: I did find yesterday that it was about 1/2 gallon low on coolant, I've topped it off and it is behaving better but I'm not convinced the problem has gone away. I haven't had a reason to let it idle for long. If you are leaking coolant eventually you will overheat. You may have a pin hole leak in the radiator or some other place. When you shut off the engine and there is a leak somewhere you will suck air from that site and then your cooling system is compromised. You may also have a bad fan switch. Link to comment Share on other sites More sharing options...
pizzaman09 Posted April 15, 2023 Author Share Posted April 15, 2023 4 hours ago, cruiser54 said: Coolant sensor and Fan switch are 2 different things. SENSOR mounts on driver side engine block and sends input to the ECM. Fan SWITCH is located low on the driver's side radiator. SENDER is located at the driver side rear of the head and sends signals to dash gauge. What temperature is the fan switch supposed to kick on at? Link to comment Share on other sites More sharing options...
87MJTIM Posted April 15, 2023 Share Posted April 15, 2023 11 minutes ago, pizzaman09 said: What temperature is the fan switch supposed to kick on at? Mine kicks on around 219* according to the REM. It shuts off around 213*. Link to comment Share on other sites More sharing options...
Ωhm Posted April 15, 2023 Share Posted April 15, 2023 Link to comment Share on other sites More sharing options...
87MJTIM Posted April 15, 2023 Share Posted April 15, 2023 Yes, but... The e-fan switch is on the cool side of the radiator - not connected to the ECU. The engine temp sensor is on the driver's side block - feeding the ECU. The REM reads the ECU, which is not the temp coming from the radiator. Link to comment Share on other sites More sharing options...
Ωhm Posted April 15, 2023 Share Posted April 15, 2023 True, location, location, location. Link to comment Share on other sites More sharing options...
pizzaman09 Posted April 15, 2023 Author Share Posted April 15, 2023 I have tested and found the viscous clutch fan is not any good. Link to comment Share on other sites More sharing options...
cruiser54 Posted April 16, 2023 Share Posted April 16, 2023 Probably not the only thing wrong. Link to comment Share on other sites More sharing options...
pizzaman09 Posted April 23, 2023 Author Share Posted April 23, 2023 To close this out. I ended up replacing the fan clutch and the electric fan switch. I found out that someone in the past had hacked the fan switch into the lower rad hose instead of plugging it into the radiator location. Notice the plug hacked into the rad hose. Link to comment Share on other sites More sharing options...
cruiser54 Posted April 23, 2023 Share Posted April 23, 2023 That "hack" was generally done when dealer installed AC was put in. Link to comment Share on other sites More sharing options...
pizzaman09 Posted April 23, 2023 Author Share Posted April 23, 2023 1 hour ago, cruiser54 said: That "hack" was generally done when dealer installed AC was put in. That must be it as I looked at my vin build sheet and it had zero mention of AC. I know the previous owner of the truck told me that the dealership that owned it had recently fixed up the AC at the request of the dealership owner's wife that liked driving around in the Comanche. Link to comment Share on other sites More sharing options...
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