89 MJ Posted August 7, 2022 Share Posted August 7, 2022 Going to and from Kenosha, I noticed the temp gauge creeping up in my 89 4.0. I was turning about 2700 RPMs at 72ish mph (4.10 gears and 31s). The temp seemed to sit right at 220 in clean air and would creep up more (225-230) when following someone. All numbers verified with an invaded thermometer. I have an open cooling system with the Mishimoto radiator and a stock thermostat. The AC was not run at all and outside temps were between 75 and 85. The temp would get that high after about an hour of driving. What can I do to keep the temps at 210 or less? I would like to bring the truck to AZ with me at some point and don’t want to deal with overheating when I’m down there. Link to comment Share on other sites More sharing options...
eaglescout526 Posted August 7, 2022 Share Posted August 7, 2022 I’m running stock on my 2.5L and never see 210. Course I probably have a slightly stuck thermostat in my favor there but that’s fine. What’s the condition of everything but the radiator? All air out? How about the fan clutch? Link to comment Share on other sites More sharing options...
89 MJ Posted August 7, 2022 Author Share Posted August 7, 2022 5 minutes ago, eaglescout526 said: I’m running stock on my 2.5L and never see 210. Course I probably have a slightly stuck thermostat in my favor there but that’s fine. What’s the condition of everything but the radiator? All air out? How about the fan clutch? Fan clutch was new with the radiator, hoses were new with the engine swap, block was flushed with the engine swap, and it was a new water pump when I got the engine. It seems to be getting plenty of airflow too. Link to comment Share on other sites More sharing options...
JMO413 Posted August 7, 2022 Share Posted August 7, 2022 Do you have a fan shroud? Just checking many people overlook the importance of them. Link to comment Share on other sites More sharing options...
89 MJ Posted August 7, 2022 Author Share Posted August 7, 2022 8 minutes ago, JMO413 said: Do you have a fan shroud? Just checking many people overlook the importance of them. I do have a good, OEM shroud on it Link to comment Share on other sites More sharing options...
JMO413 Posted August 7, 2022 Share Posted August 7, 2022 I figured you did. Good luck you have already replaced all the normal culprits. Link to comment Share on other sites More sharing options...
eaglescout526 Posted August 7, 2022 Share Posted August 7, 2022 Maybe the T-stat isn’t opening up all the way. Link to comment Share on other sites More sharing options...
89 MJ Posted August 7, 2022 Author Share Posted August 7, 2022 14 minutes ago, JMO413 said: I figured you did. Good luck you have already replaced all the normal culprits. Thank you 5 minutes ago, eaglescout526 said: Maybe the T-stat isn’t opening up all the way. At this point, that’s where I am at too. Link to comment Share on other sites More sharing options...
eaglescout526 Posted August 7, 2022 Share Posted August 7, 2022 That’s kinda the only thing I can think of. It seems that t-stats aren’t being made to work like they should. Like I even put mopar in mine. Unless My mopar unit just runs really cool, there’s gotta be something wrong with the quality of all the stats. Link to comment Share on other sites More sharing options...
Eagle Posted August 8, 2022 Share Posted August 8, 2022 Does the lower radiator hose have a spring in it? If not, the hose may start to collapse at high RPM when hot, which reduces the coolant flow. Link to comment Share on other sites More sharing options...
cruiser54 Posted August 8, 2022 Share Posted August 8, 2022 I would try a new Mopar stat. Are you considering 2700 RPM high? Link to comment Share on other sites More sharing options...
89 MJ Posted August 9, 2022 Author Share Posted August 9, 2022 On 8/7/2022 at 4:14 PM, eaglescout526 said: That’s kinda the only thing I can think of. It seems that t-stats aren’t being made to work like they should. Like I even put mopar in mine. Unless My mopar unit just runs really cool, there’s gotta be something wrong with the quality of all the stats. I’m think I’ll probably replace it, it’s cheap enough that it’s not a big deal if it doesn’t solve the issue. On 8/7/2022 at 7:37 PM, Eagle said: Does the lower radiator hose have a spring in it? If not, the hose may start to collapse at high RPM when hot, which reduces the coolant flow. I believe that it does, I’ll have to make sure though. On 8/8/2022 at 6:56 AM, cruiser54 said: I would try a new Mopar stat. Are you considering 2700 RPM high? I probably will. Considering everything else in our collection turns 2100 at 70, I consider 2700 at 70 pretty high Link to comment Share on other sites More sharing options...
cruiser54 Posted August 9, 2022 Share Posted August 9, 2022 2700 RPM is not high for a 4.0. Sure you're not lugging it? Link to comment Share on other sites More sharing options...
lejeune981 Posted August 9, 2022 Share Posted August 9, 2022 1 hour ago, cruiser54 said: 2700 RPM is not high for a 4.0. Sure you're not lugging it? So my jeep with a combo of 5.13 gears and 31 inch tires… spinning at 3000 to do 70mph isn’t spinning her too fast? think 75 mph is around 3200 it will deff go faster but I get worried running her above 3k mine heats up too so I’ve gotta run the aux fan to keep her around 210 while cruzing these Florida’s highways Link to comment Share on other sites More sharing options...
cruiser54 Posted August 9, 2022 Share Posted August 9, 2022 No worries. It isn't a tractor motor. It's probably the most capable, flexible, and longest running straight 6 engines ever built. Drive it like you stole it if you want to. Ever see the speedo needle point straight down for over 2 miles? I have. Still have that Jeep with over 200K miles. Link to comment Share on other sites More sharing options...
lejeune981 Posted August 9, 2022 Share Posted August 9, 2022 Good to know.. she rides smooth at 80 but I’m not ballsy enough to find out how fast it will go lol So she is safe to roll at 3000 to 3500 rpm for long distances ? I go to Tampa bay and the gulf about every weekend to go fishin so it’s a good hour drive at 3k I know 4.0s are nearly indestructible.. but I seem to have a knack at breaking the unbreakable 😂 Link to comment Share on other sites More sharing options...
lejeune981 Posted August 9, 2022 Share Posted August 9, 2022 P.s. your renix page is a life saver Link to comment Share on other sites More sharing options...
cruiser54 Posted August 9, 2022 Share Posted August 9, 2022 Might burn more fuel and might not. Strong enough to do that easily. With an auto trans, they shift out of one gear and up to the next at 4800 RPM ya know. Glad you're enjoying the Renix Tips. Link to comment Share on other sites More sharing options...
lejeune981 Posted August 10, 2022 Share Posted August 10, 2022 50 minutes ago, cruiser54 said: Might burn more fuel and might not. Strong enough to do that easily. With an auto trans, they shift out of one gear and up to the next at 4800 RPM ya know. Glad you're enjoying the Renix Tips. Link to comment Share on other sites More sharing options...
lejeune981 Posted August 10, 2022 Share Posted August 10, 2022 Oh she loves her recycled Dino’s expecially on the highway but I think that’s due to an issue somewhere that I haven’t quite found yet.. it used to do better mpg wise mines a 5 speed but good to know the autos shift at 4800 Link to comment Share on other sites More sharing options...
cruiser54 Posted August 10, 2022 Share Posted August 10, 2022 Have you completed Tips 1,3,4 and 5 yet? Tell us more about your thermostat. Are you running a good 16 pound radiator cap? Link to comment Share on other sites More sharing options...
89 MJ Posted August 10, 2022 Author Share Posted August 10, 2022 16 hours ago, cruiser54 said: 2700 RPM is not high for a 4.0. Sure you're not lugging it? Glad to hear it, it doesn’t get lugged Link to comment Share on other sites More sharing options...
lejeune981 Posted August 10, 2022 Share Posted August 10, 2022 13 hours ago, cruiser54 said: Have you completed Tips 1,3,4 and 5 yet? Tell us more about your thermostat. Are you running a good 16 pound radiator cap? Haven’t messed with the coil yet, but 1,3,5 yes unknown on thermostat and still running the sealed system so no cap deleted the c101 a couple weeks ago Link to comment Share on other sites More sharing options...
Andy in Pa Posted August 10, 2022 Share Posted August 10, 2022 I have not seen mention of this, but to the OP, do you have an electric fan? Does it run on the temp switch? Was it running when it reached 210*F? Honestly, I can't remember anymore if the Renix fans come on at 210*F, but it would be easy enough to activate if you still have the temp switch in your radiator. Its located just above the outlet line at the bottom drivers side of the radiator. I suppose the other thing to try is to turn on the AC, as it should turn on the electric fan as well. Link to comment Share on other sites More sharing options...
cruiser54 Posted August 10, 2022 Share Posted August 10, 2022 218* or 208* Link to comment Share on other sites More sharing options...
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