CO MJ Posted July 8, 2021 Share Posted July 8, 2021 Hi all, I recently picked up an 89 renix 4.0 4x4 MJ and it's running pretty consistently at about 250. It was originally closed cooling, but I accidentally popped the pressure bottle and decided to go ahead and just swap over to the open system with a new radiator and overflow bottle. I removed the heater control valve as well. So, fortunately I don't have to futz around with the closed system, but I'm still running just as hot. Here's everything I've tried so far: I flushed the originally coolant, which was not particularly cruddy looking, but figured that was a good starting point. I think I did a pretty good job cleaning out the engine and the heater core. I've since ran a few changes of cleaner fluid and distilled water through it. I replaced what looked like the original thermostat with a new stat. I boiled both of them and they appeared to open at 195 as intended. I have checked my gauge and read the sensor with an IR thermometer and I believe them to be working and reading correctly. I have checked my fan clutch and it seems to be in great condition as well as the blades and my ducts. My efan was not originally running, but I have bypassed the AC low pressure switch to have it running all the time (turns on if I jump the temp sensor from the rad as well but i haven't ordered a new sensor yet), but that has not helped temps. I did a dry compression test and got a 130 across all 6 cylinders (didn't have any oil at the time, but numbers seemed good so I haven't done a wet test yet) I am reading about 190F at the upper rad hose and about 170F at the lower hose. Someone told me on a facebook group that I should be getting about 20F difference which seems right, not sure if those temps themselves are high or low though. My tailpipe is shot and leaking like crazy, and there is a small hole where the muffler dumps into the tailpipe, but I assume this is irrelevant. As best I can tell there are no leaks elsewhere in the pipes or around the cat. I just failed emissions with high CO. Not sure if that's correlated. As far as I am aware there is no smell of exhaust in the bay, nor any strange noises. I am suspecting my water pump is pretty corroded or my head gasket leaking exhaust into the coolant. I also saw a video talking about the harmonic balancer wearing out that can cause overheating as well, but by eye it looks fine, not sure if there's any other clues without pulling it. Keep in mind I'm just a dingus with some wrenches, if I missed any critical info please let me know, or if there are any tests I should be able to do. I'll keep the original post up to date with anything I might have missed as it comes to mind. Any advice appreciated! Link to comment Share on other sites More sharing options...
87MJTIM Posted July 8, 2021 Share Posted July 8, 2021 Did you replace the hoses, especially the lower one? Those are supposed to have an internal spring to keep the hose from collapsing from the water pump suction. If the spring is gone or the hose is squishy, then the hose may collapse, restricting coolant flow. Link to comment Share on other sites More sharing options...
CO MJ Posted July 8, 2021 Author Share Posted July 8, 2021 1 minute ago, 87MJTIM said: Did you replace the hoses, especially the lower one? Those are supposed to have an internal spring to keep the hose from collapsing from the water pump suction. If the spring is gone or the hose is squishy, then the hose may collapse, restricting coolant flow. Hi! The upper hose still had a clean sticker on it. The lower hose is suspiciously clean as well, so I think it's fairly new. I replaced the two heater hoses when I deleted the heater control valve. I actually checked for that spring this morning and it is not there. I ordered a spring someone else said fits, but I also checked and the hose looks to be fine even at high RPM. I am sitting at about 250 at idle though so I suspect even if I am collapsing at speed, I must have another issue elsewhere. Link to comment Share on other sites More sharing options...
Ωhm Posted July 8, 2021 Share Posted July 8, 2021 Welcome to the CC Forum. You got your radiator shroud in place? You jumped your AC Low Pressure Switch, does your AC clutch engage when EFan is ON? Link to comment Share on other sites More sharing options...
AZJeff Posted July 8, 2021 Share Posted July 8, 2021 Here is the list of stuff to check whenever and MJ/XJ overheats: 1. clean coolant. 2. good pressure cap or pressure bottle/cap (This is surprisingly a commonly overlooked issue) 3. good viscous fan clutch (its hard to test for this, so if the clutch is old, just replace it) 4. fan shroud (another overlooked, but critical, piece) 5. elect. cooling fan coming on as needed 6. good thermostat 7. a radiator that is free of external debris, and that is free of clogged passages (since it's hard to see inside an XJ/MJ radiator, use the coolant cleanliness as a guide to whether you should be considering a new rad. A neglected cooling system will destroy even a brand new rad in short order. 8. firm/new cooling hoses. Link to comment Share on other sites More sharing options...
CO MJ Posted July 8, 2021 Author Share Posted July 8, 2021 27 minutes ago, Ωhm said: Welcome to the CC Forum. You got your radiator shroud in place? You jumped your AC Low Pressure Switch, does your AC clutch engage when EFan is ON? Radiator shroud is in place. AC clutch does come on but I have it unplugged for now so I don't burn it out, I'm out of refrigerant. 2 minutes ago, AZJeff said: Here is the list of stuff to check whenever and MJ/XJ overheats: 1. clean coolant. 2. good pressure cap or pressure bottle/cap (This is surprisingly a commonly overlooked issue) 3. good viscous fan clutch (its hard to test for this, so if the clutch is old, just replace it) 4. fan shroud (another overlooked, but critical, piece) 5. elect. cooling fan coming on as needed 6. good thermostat 7. a radiator that is free of external debris, and that is free of clogged passages (since it's hard to see inside an XJ/MJ radiator, use the coolant cleanliness as a guide to whether you should be considering a new rad. A neglected cooling system will destroy even a brand new rad in short order. 8. firm/new cooling hoses. 1. Coolant cleaned 2. Pretty sure my rad cap is fine 3. Fan clutch feels great but maybe I'll look into a new one anyways 4. All my shrouding is in good shape 5. Fan is on 6. Tested my new thermostat and working 7. Brand New rad and my water is staying pretty clean after a few flushes 8. Cooling hoses feel pretty good to me aside from the missing spring but I'm not collapsing Link to comment Share on other sites More sharing options...
87MJTIM Posted July 8, 2021 Share Posted July 8, 2021 proper water pump? Some pumps have the blades facing opposite direction. The belt spins the pump "backwards." I don't know how to check it when mounted. Link to comment Share on other sites More sharing options...
CO MJ Posted July 8, 2021 Author Share Posted July 8, 2021 6 minutes ago, 87MJTIM said: proper water pump? Some pumps have the blades facing opposite direction. The belt spins the pump "backwards." I don't know how to check it when mounted. I think that'll be the next thing I check. I definitely have some flow that I can see at the rad cap but Ive seen quite a few that have corroded to the point they definitely effect cooling Link to comment Share on other sites More sharing options...
jdog Posted July 9, 2021 Share Posted July 9, 2021 Plain water or 50/50 mix? Link to comment Share on other sites More sharing options...
CO MJ Posted July 9, 2021 Author Share Posted July 9, 2021 29 minutes ago, jdog said: Plain water or 50/50 mix? I did a 50/50 mix after the first flush but it was still running hot. I'm running just water right now Link to comment Share on other sites More sharing options...
cruiser54 Posted July 9, 2021 Share Posted July 9, 2021 I'd pull the water pump. A bad radiator cap could also be an issue. The spring was only in the hose to keep the hose from collapsing when the cooling system was filled using vacuum on the assembly line. Can't hurt to have it, but I've never worried about it and I live in Arizona FWIW. You can rent/borrow a tester that checks for exhaust being present in the cooling system. Called "Block Check" IIRC. Might wanna do that first. Link to comment Share on other sites More sharing options...
AZJeff Posted July 9, 2021 Share Posted July 9, 2021 A rad pressure cap that won’t hold pressure WILL cause these engines to overheat. Nominal operating temperatures are right about boiling point of water, and the combination of antifreeze and the pressure cap will raise the boiling point considerably. Given the cost of a rad cap, I would put a new one on on general principles. Link to comment Share on other sites More sharing options...
CO MJ Posted July 9, 2021 Author Share Posted July 9, 2021 6 hours ago, cruiser54 said: I'd pull the water pump. A bad radiator cap could also be an issue. The spring was only in the hose to keep the hose from collapsing when the cooling system was filled using vacuum on the assembly line. Can't hurt to have it, but I've never worried about it and I live in Arizona FWIW. You can rent/borrow a tester that checks for exhaust being present in the cooling system. Called "Block Check" IIRC. Might wanna do that first. Thanks cruiser. I'll look into the tester. A few friends told me that you'd have to drive quite a bit for the gasses to leave enough trace for the tests to pick up, but certainly beats taking the head off and not finding a leak, I'll give it a go. I think I will pull the pump first this weekend. 1 hour ago, AZJeff said: A rad pressure cap that won’t hold pressure WILL cause these engines to overheat. Nominal operating temperatures are right about boiling point of water, and the combination of antifreeze and the pressure cap will raise the boiling point considerably. Given the cost of a rad cap, I would put a new one on on general principles. I bought a brand new rad cap with the radiator. It's definitely not leaking any water past the cap, and it looks like the system has taken in some of the water from my expansion bottle, not sure if there's any other way to know if it's working properly. I suppose since I'm currently water only it could be boiling but not overpressurizing the cap and causing an issue? I will probably try another flush and a 50/50 mix after I do the water pump this weekend. Link to comment Share on other sites More sharing options...
cruiser54 Posted July 9, 2021 Share Posted July 9, 2021 Exhaust gasses show right up with the tester. Link to comment Share on other sites More sharing options...
Eagle Posted July 10, 2021 Share Posted July 10, 2021 On 7/8/2021 at 5:38 PM, CO MJ said: Hi all, I recently picked up an 89 renix 4.0 4x4 MJ and it's running pretty consistently at about 250. It was originally closed cooling, but I accidentally popped the pressure bottle and decided to go ahead and just swap over to the open system with a new radiator and overflow bottle. I removed the heater control valve as well. So, fortunately I don't have to futz around with the closed system, but I'm still running just as hot. Here's everything I've tried so far: How do you know it's running at 250 degrees? There's no marked point on the temperature gauge for 250. Is the needle in the red? Link to comment Share on other sites More sharing options...
CO MJ Posted July 10, 2021 Author Share Posted July 10, 2021 20 hours ago, cruiser54 said: Exhaust gasses show right up with the tester. Cool, thanks, I picked up a tester yesterday. Once I check the water pump I'll drive a bit and see what it says! 8 hours ago, Eagle said: How do you know it's running at 250 degrees? There's no marked point on the temperature gauge for 250. Is the needle in the red? I've been using an IR thermometer to read the temp at the block sensor. My needle spends most of it's time at or in the red. Link to comment Share on other sites More sharing options...
watchamakalit Posted July 11, 2021 Share Posted July 11, 2021 On 7/8/2021 at 9:05 PM, CO MJ said: I did a 50/50 mix after the first flush but it was still running hot. I'm running just water right now I am not a chemist but this could be part of the problem. I am pretty sure that the 50/50 antifreeze mix not only has a lower freezing point than straight water but also a higher boiling point. I believe it will effect cooling just as it does freezing. Better to return as much of the system to its design parameters before trying to chase a rabbit. Link to comment Share on other sites More sharing options...
cruiser54 Posted July 11, 2021 Share Posted July 11, 2021 The type of coolant mix, or the lack of it altogether, will not cause an overheat condition. Link to comment Share on other sites More sharing options...
watchamakalit Posted July 11, 2021 Share Posted July 11, 2021 I didn't mean it to be cause of the problem. Just possible contributing factor? Kinda like a death wobble senario. No one bad element but a combination of slightly sub par products. Link to comment Share on other sites More sharing options...
cruiser54 Posted July 11, 2021 Share Posted July 11, 2021 Water boils at 212*F at sea level. Coolant just raises the boiling point and keeps the system from corrosion. Everything else being good in the cooling system, it would run right at the thermostat rating. Link to comment Share on other sites More sharing options...
MiNi Beast Posted July 11, 2021 Share Posted July 11, 2021 5 hours ago, cruiser54 said: The type of coolant mix, or the lack of it altogether, will not cause an overheat condition. I disagree with you here. proper mixture is important to overheating issues. Link to comment Share on other sites More sharing options...
cruiser54 Posted July 11, 2021 Share Posted July 11, 2021 Okay. If you say so. Link to comment Share on other sites More sharing options...
MiNi Beast Posted July 11, 2021 Share Posted July 11, 2021 1 hour ago, cruiser54 said: Okay. If you say so. Thanks. I APPRECIATE YOUR acknowledgement. Link to comment Share on other sites More sharing options...
AZJeff Posted July 11, 2021 Share Posted July 11, 2021 8 hours ago, cruiser54 said: Water boils at 212*F at sea level. Coolant just raises the boiling point and keeps the system from corrosion. Everything else being good in the cooling system, it would run right at the thermostat rating. Cruiser, the key thing you mentioned might be overlooked to ssome degree: "everything else being good" Plain water boils at 212* Put a working 16lb pressure cap on the cooling system, and it raises the boiling point to 252* Add a 50/50 mix, and the boiling point is now 267* If the OP's engine is TRULY overheating (as in getting hotter than about 215* or thereabouts, I would suspect some sort of faiiure to hold pressure as the most likely culprit. (Unless the dreaded head gasket failure that has been thrown out is proven to be a non-issue.) Link to comment Share on other sites More sharing options...
cruiser54 Posted July 12, 2021 Share Posted July 12, 2021 Correct. Something is wrong and it has nothing to do with coolant concentration. It's pressure, circulation, or head gasket. Link to comment Share on other sites More sharing options...
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