Have I cooked my 4.0? Epic mistake on long trip

Bammo68

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Hi Guys,

'99 4.0L with 80,000 miles on the clock. Recently retrofitted factory aircon to it (which works a treat!) which meant the radiator was out which is when I done stuffed up!

Did a long (500mile) drive yesterday in hot weather when the engine suddenly started making a loud ticking noise, steam started coming out, the temperature gauge pegged into the red and then the engine stalled. All happened within about 20 seconds from the first noise to the stall. Pulled over and discovered the bottom radiator hose had come loose as I hadn't retightened the hose clamp after the aircon fit so massive fail on my behalf.

Had access to enough water to get the radiator refilled (took nearly 2 gallons) and she restarted first pop. Completed the rest of the journey with no major problems but a couple of small indicators that things may not be 100% with the engine and wanted an opinion on whether I might have done permanent damage to the head.

The Good:
  • No sign of water in the oil
  • No sign of exhaust bubbles in the radiator
  • No obvious vapour signs out the exhaust
  • Power remains good and it drives just fine
  • No obvious coolant loss
The Bad:
  • Temperature during the return trip was slightly higher by 3 or 4 degrees but it was hot with lots of hills and aircon on so unclear if that was just the environment or running tap water in the radiator
  • The oil pressure was down slightly and looked to be about a pint low on oil but I had just done an oil change and may have slightly underfilled it. Added a bit more and oil pressure stays on the same reading (about 20PSI) as before but after an extended run if I come to a complete halt the oil pressure drops to nearly zero and the check gauges light comes on - goes away pretty quickly. I've not seen that before but may not have been paying attention.
  • When I finished the trip I noticed a noise like boiling or bubbling possibly from the radiator overflow tank - not sure if that's normal

I'm going to replace the radiator, hoses, water pump and thermostat regardless as the radiator is end of life and the water looks pretty cruddy in there even after a recent flush.

Should I be considering lifting the head and replacing the head gasket or should I just keep driving it and keep an eye on it?
 

KennethS

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You may be OK, but if you have concerns about the head gasket or the head itself you can rent a test kit from the local auto parts store to check for combustion gases in the cooling system. I did that on mine and it was very easy (luckily with negative results).

The original radiator on mine split while the wife was on the interstate. Similar to your issue, it happened quickly. I told her to keep driving as she was near the exit, and the engine died at the end of the exit ramp. After swapping the radiator and refilling coolant, it ran fine. That was nearly 10 years and 30,000 miles ago and it’s still running strongly.

So again, you may be OK. These are tough engines.
 
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Moglocker

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Hi Guys,

'99 4.0L with 80,000 miles on the clock. Recently retrofitted factory aircon to it (which works a treat!) which meant the radiator was out which is when I done stuffed up!

Did a long (500mile) drive yesterday in hot weather when the engine suddenly started making a loud ticking noise, steam started coming out, the temperature gauge pegged into the red and then the engine stalled. All happened within about 20 seconds from the first noise to the stall. Pulled over and discovered the bottom radiator hose had come loose as I hadn't retightened the hose clamp after the aircon fit so massive fail on my behalf.

Had access to enough water to get the radiator refilled (took nearly 2 gallons) and she restarted first pop. Completed the rest of the journey with no major problems but a couple of small indicators that things may not be 100% with the engine and wanted an opinion on whether I might have done permanent damage to the head.

The Good:
  • No sign of water in the oil
  • No sign of exhaust bubbles in the radiator
  • No obvious vapour signs out the exhaust
  • Power remains good and it drives just fine
  • No obvious coolant loss
The Bad:
  • Temperature during the return trip was slightly higher by 3 or 4 degrees but it was hot with lots of hills and aircon on so unclear if that was just the environment or running tap water in the radiator
  • The oil pressure was down slightly and looked to be about a pint low on oil but I had just done an oil change and may have slightly underfilled it. Added a bit more and oil pressure stays on the same reading (about 20PSI) as before but after an extended run if I come to a complete halt the oil pressure drops to nearly zero and the check gauges light comes on - goes away pretty quickly. I've not seen that before but may not have been paying attention.
  • When I finished the trip I noticed a noise like boiling or bubbling possibly from the radiator overflow tank - not sure if that's normal

I'm going to replace the radiator, hoses, water pump and thermostat regardless as the radiator is end of life and the water looks pretty cruddy in there even after a recent flush.

Should I be considering lifting the head and replacing the head gasket or should I just keep driving it and keep an eye on it?

Was the oil pressure always that low before?
 
OP
Bammo68

Bammo68

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On my RHD TJ the oil pressure gauge has two numbers, TDC is a "3" and maximum is "5.4". Roughly translates to 43psi and 78psi. When I first start its usually around the 45-50psi but rapidly settles down to about 23psi but that's a pretty rough guess given how coarse the gauge is! Its always been at that point, after my last oil change at Christmas it was probably closer to 20psi but after topping it up with about a quart it went back to ~23psi and doesn't move very much from there other than dropping to near zero when I pull up after a long drive. Its drops right down and then slowly comes back up or if I give it a bit of gas it pops right back up to 23.
 

TheBoogieman

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You said you added water to the radiator. You didn't mention antifreeze. That would make the temps higher. Get a new Mopar oil sending unit for the zero oil pressure reading and check gauges light coming on.
p.s. I had the radiator hose come loose twice on my XJ. It didn't do any damage because I added water after a short drive to the store.
 
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Bammo68

Bammo68

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You said you added water to the radiator. You didn't mention antifreeze. That would make the temps higher. Get a new Mopar oil sending unit for the zero oil pressure reading and check gauges light coming on.
p.s. I had the radiator hose come loose twice on my XJ. It didn't do any damage because I added water after a short drive to the store.

Yep plain water was all we had - we were 100km from the nearest town! I've ordered a new radiator, water pump, thermostat etc just because the water in there now looks awful, full of muck and very brown in colour so going to flush the heck out of it and put in all new components. Curious as to why you recommend a new oil pressure sending unit given mine seems to be doing its job?
 

B1Toad

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You said you added water to the radiator. You didn't mention antifreeze. That would make the temps higher. Get a new Mopar oil sending unit for the zero oil pressure reading and check gauges light coming on.
p.s. I had the radiator hose come loose twice on my XJ. It didn't do any damage because I added water after a short drive to the store.

Not to question your wisdom but I always heard that water alone transferred heat better than coolant but we use coolant for it's anti-corrosive properties and resistance to freezing and boiling. I believe if you pour 100% coolant into the cooling system with no water it will have less cooling ability, more cooling ability at 50:50 and the highest cooling ability at 100% water (until it boils at which point you will lose cooling ability).
 

Jerry Bransford

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Yes water is a better conductor of heat than coolant is, coolant's purpose is to reduce its freezing point and to provide a protective lubricant for the water pump and cooling system. You no doubt just got some air in the cooling system which with enough time will make its way out through the upper hose to the top of the radiator. The new thermostat will likely have a small bleed hole on its flange, make sure to position the hole at the top when you place it into the thermostat housing bolted to the head. That hole is there to help get rid of trapped air. If the thermostat you buy doesn't have a bleed hole drill your own with a 1/8" drill.

Thermostat Factory Hole.jpg
 

SkylinesSuck

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Oil pressure sounds normal but change it as you've likely "burnt" the oil. Get all the remaining air bled from your coolant system while also running at least a bit of antifreeze. Maybe 30% minimum? Sounds like you didn't do any damage but a compression check would be a good idea if you want to be thorough.
 
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Gilaguy23

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You said you added water to the radiator. You didn't mention antifreeze. That would make the temps higher. Get a new Mopar oil sending unit for the zero oil pressure reading and check gauges light coming on.
p.s. I had the radiator hose come loose twice on my XJ. It didn't do any damage because I added water after a short drive to the store.

Does water transfer heat better than antifreeze?
Water has superior heat transfer properties compared to propylene or ethylene glycol and is more frequently used in the southern half of the United States. Water is also cheaper than glycol and, in most cases, will result in a smaller unit selection while requiring less pumping
 
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NashvilleTJ

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Yes water is a better conductor of heat than coolant is, coolant's purpose is to reduce its freezing point and to provide a protective lubricant for the water pump and cooling system. You no doubt just got some air in the cooling system which with enough time will make its way out through the upper hose to the top of the radiator. The new thermostat will likely have a small bleed hole on its flange, make sure to position the hole at the top when you place it into the thermostat housing bolted to the head. That hole is there to help get rid of trapped air. If the thermostat you buy doesn't have a bleed hole drill your own with a 1/8" drill.

View attachment 394190

Does antifreeze have a higher boiling point than water at a given pressure? I've always assumed that it did, but just realized that I don't actually know.
 
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B1Toad

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  • When I finished the trip I noticed a noise like boiling or bubbling possibly from the radiator overflow tank - not sure if that's normal

Some AC systems will make a gurgling sound after shutting down as the refrigerant pressure on the high side equalizes into the low side.
 

BlueC

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Does antifreeze have a higher boiling point than water at a given pressure? I've always assumed that it did, but just realized that I don't actually know.

You know, I had always assumed antifreeze had no effect on boiling point. I thought pressure in the system was the only thing that raised the boiling point. A quick look online and it looks like glycol does raise the boiling point some.

1674486134559.png


1674486178789.png

 

NashvilleTJ

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You know, I had always assumed antifreeze had no effect on boiling point. I thought pressure in the system was the only thing that raised the boiling point. A quick look online and it looks like glycol does raise the boiling point some.

View attachment 394192
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View attachment 394193
[/URL]

Great info, Blue. 15 degrees with the cap on is a decent increase.
 

SkylinesSuck

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As posted, antifreeze raises the boiling point of water, fights corrosion, and it lubricates the water pump seal. In addition to keeping things from freezing of course. If your cooling system is in good shape, the small advantage you get in cooling reserve by running straight water will be miniscule compared to the downsides. If your system isn't in the best shape and you need to run straight water to stay cool, you need to fix your system.
 

Irun

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While water may do a better job of heat transfer initially, using water only will ultimately lead to degraded cooling capacity. The amount of corrosion that builds up in the cooling system, with just a water based coolant, will happen rapidly, causing the clear water to turn brown. Over time, in just a few months, that "brown" solution will begin to plug up the radiator and heater core. Even if I could run just water, I'd not want the hassle of flushing the system every few months and replacing water pumps more frequently. Those trade-offs aren't worth it, for the nominal difference in cooling cost.
 

Zorba

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I can tell you from personal experience that anti-freeze/coolant is a poorer conductor of heat than water is. Idiot mechanic put 1/3rd more coolant into the old MBZ than was called for - it ran warmer than it should have until I diluted it down to something closer to a 50/50 mixture.
 
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Moglocker

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You said you added water to the radiator. You didn't mention antifreeze. That would make the temps higher. Get a new Mopar oil sending unit for the zero oil pressure reading and check gauges light coming on.
p.s. I had the radiator hose come loose twice on my XJ. It didn't do any damage because I added water after a short drive to the store.

This here,these things run on the edge of hot,everything has to be right as rain,including mopar radiator and a good 50-50 mix
 
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