cdtx_2011 Posted February 17 Share Posted February 17 Hey Guys, I have 1988 4.0l, prior to changing the temp sensor at the back of the head the gauge would never get above 160 indicated on the dash. I changed the sensor and got the same result, when i stepped out of the truck and back in (20 seconds) it had jumped to 215-220. How do i go about troubleshooting the gauge? I'm not terribly worried about the higher temp at this time, i just want to be sure I'm getting the correct reading (and yes, I'm buying an infared gun soon!). thanks! Link to comment Share on other sites More sharing options...
eaglescout526 Posted February 17 Share Posted February 17 Maybe your t-stat is stuck or the wrong temp? this is where I would start if my temp was reading low. Have you confirmed the temp gauge is accurate with a infrared gun? Link to comment Share on other sites More sharing options...
cdtx_2011 Posted February 17 Author Share Posted February 17 Water pump and thermostat are brand new. Picking up an infared gun this weekend. Link to comment Share on other sites More sharing options...
eaglescout526 Posted February 17 Share Posted February 17 195* stat? Link to comment Share on other sites More sharing options...
cdtx_2011 Posted February 17 Author Share Posted February 17 Correct, 195 with 3/16 hole drilled at the 12 o’clock. Link to comment Share on other sites More sharing options...
cruiser54 Posted February 17 Share Posted February 17 MOPAR 195* stat? Link to comment Share on other sites More sharing options...
cdtx_2011 Posted February 17 Author Share Posted February 17 Motorad Link to comment Share on other sites More sharing options...
cruiser54 Posted February 17 Share Posted February 17 That could be your problem right there. Link to comment Share on other sites More sharing options...
cdtx_2011 Posted February 17 Author Share Posted February 17 They're cheap enough that i'm willing to replace again, however the sticking was happening with the old thermostat other than it never read above 160 on the gauge which lead me to go ahead and change the sensor. That's why i'm weary of the gauge reading vs the thermostat. I probably would have not changed the thermostat but when i got the truck it had a replacement thermostat in the center console that was clearly never change before the truck was parked for 20 years. I'll try the temperature gun and see if things are matching up. Link to comment Share on other sites More sharing options...
eaglescout526 Posted February 17 Share Posted February 17 4 hours ago, cruiser54 said: MOPAR 195* stat? 1 hour ago, cdtx_2011 said: Motorad From when I ordered mine from mopar, it was made by motorad. Link to comment Share on other sites More sharing options...
cruiser54 Posted February 17 Share Posted February 17 That is correct. BUT, the aftermarket Motorad thermostats don't hold a candle to the ones they make for Mopar. Link to comment Share on other sites More sharing options...
eaglescout526 Posted February 17 Share Posted February 17 27 minutes ago, cruiser54 said: That is correct. BUT, the aftermarket Motorad thermostats don't hold a candle to the ones they make for Mopar. I want to agree with you but I also don’t want to disagree with you there either. I put in a mopar motorad a few years ago. Now it’s opening up either a bit to early or it’s partially stuck. One of the two and I hate changing the t-stat. Hate the idea of changing it frequently too. Link to comment Share on other sites More sharing options...
cruiser54 Posted February 17 Share Posted February 17 Wow. My experience has been: Three 4.0s in the family. I put a brand new Stant SuperStat 195* in each one. All of them exhibited the same symptoms. took a while to warm up. Ran a little cool and got rather hot before opening up and cooling down. Warranteed all 3 and replaced with new SuperStats. Same symptoms. I bought a new 8983501426XX stat from the dealer and put it in one of the 4.0s. Warmed up quickly. Temp stayed rock solid with no swing at the top end. So, I replaced the other 2 SuperStats with factory Mopar. Same results. You think you don't like replacing stats? That was 9 times!!!! Link to comment Share on other sites More sharing options...
eaglescout526 Posted February 17 Share Posted February 17 Yeesh! Link to comment Share on other sites More sharing options...
schardein Posted February 18 Share Posted February 18 In tech school I was taught to bench test every new thermostat in a pot of water on the stove top (with a thermometer), before installation. And this was 36 years ago. So questionable thermostats aren't something new or recent. I guess a bench test might not pick up funky operation at operating temp, but it will tell you if it is opening at the right temp, if it is opening smoothly, and if it is closing smoothly. During bench testing I've seen ones not open at a full boil, I've seen them open well before their rated temp, and I've seen them stick partway open when cooling down. I don't recall the brands. And I haven't changed a thermostat in years. I trust one that's 20 years old and working before I trust a brand new one. Link to comment Share on other sites More sharing options...
pizzaman09 Posted February 18 Share Posted February 18 How is your cooling system at holding pressure? I assume it's still the Renix closed system. My truck would run cool until it sat and idled, then it would spike in temperature. Replacing the expansion tank with a new one that didn't have a slow leak fixed everything. Link to comment Share on other sites More sharing options...
cdtx_2011 Posted February 18 Author Share Posted February 18 2 hours ago, pizzaman09 said: How is your cooling system at holding pressure? I assume it's still the Renix closed system. My truck would run cool until it sat and idled, then it would spike in temperature. Replacing the expansion tank with a new one that didn't have a slow leak fixed everything. I didn’t think to check. It definitely doesn’t leak fluid but i don't know if the cap is holding pressure. I’ll check today. Link to comment Share on other sites More sharing options...
cruiser54 Posted February 18 Share Posted February 18 Is the cooling system in your vehicle a Renix type for sure? Link to comment Share on other sites More sharing options...
cdtx_2011 Posted February 19 Author Share Posted February 19 3 hours ago, cruiser54 said: Is the cooling system in your vehicle a Renix type for sure? Link to comment Share on other sites More sharing options...
cruiser54 Posted February 19 Share Posted February 19 Here's the issue with that system. The caps don't seal well and the bottle distorts/cracks/ blows up. If you're anywhere needing a radiator, switch to an open cooling system. Easy as pie. Link to comment Share on other sites More sharing options...
cdtx_2011 Posted February 20 Author Share Posted February 20 Update. Infrared gun pointed at the upper cooling hose more or less matches the dash gauge. Temp is ranging from 205-215 while idling in the driveway. So i’ll cross that anxiety off the list and move on. Maybe the gauge just needed to loosen up after sitting 20 years? Link to comment Share on other sites More sharing options...
cruiser54 Posted February 20 Share Posted February 20 Go with it!! Link to comment Share on other sites More sharing options...
Airborne Janitor Posted February 20 Share Posted February 20 I replaced an aftermarket coolant temp sensor with a Mopar one and watched my temps drop 15* at the gauge. Mopar 53005309 is what you want. Link to comment Share on other sites More sharing options...
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