Mystery coolant leak / overheating

[4speedhandler]

ok so i have in the past few years replaced the radiator when it started leaking, and the water pump when it failed. i replaced hoses and flushed the system each time. over the past 2-3 months i've been trying to track a coolant leak and having no luck. it will run fine and not leak as far as i can tell from coolant level for a few weeks then out of nowhere im out of coolant or it will overheat horrendously out of nowhere. the past two times it hasnt blown steam or had the white exhaust clouds of doom but when it cools enough to pull the cap theres nothing in there and i cant find a leak or puddle or anything. i've added the UV dye with no luck.

help me out here guys i need to figure this out and fix it asap now as its impacting my ability to get to work.

 

[CharlesHS]

Since you changed the radiator and water pump; we should assume they are good (I hope).
You didn't state whether you replaced the radiator cap with an 18# cap or whether the thermostat was replaced and what the temperature rating is. Have you checked the condition of the heater core ? Do you smell a sweet smell inside the cab ?

 

[Flivver250]

For odd ones like this, the first thing to do is check the appearance of your oil and coolant. Is the oil milky? Coolant oily? Either could be indicative of a head gasket leak. Or potentially cracked head I suppose. After checking fluids I would use a pressure tester on the cooling system. Top off the coolant (you can just add water for testing if it is empty), pump up the pressure and look for leaks. Usually the cause is an obvious leak in stealth mode.

https://www.amazon.com/gp/product/B0002SRGWU/?tag=wranglerorg-20

 

[4speedhandler]

Since you changed the radiator and water pump; we should assume they are good (I hope).
You didn't state whether you replaced the radiator cap with an 18# cap or whether the thermostat was replaced and what the temperature rating is. Have you checked the condition of the heater core ? Do you smell a sweet smell inside the cab ?

i guess i missed a few details. i put a new radiator cap on when i did the radiator and when i did the water pump both times with the OEM replacement from NAPA.
I havent done the thermostat yet as i didnt have easy access to one either time and i was in a time crunch.

For odd ones like this, the first thing to do is check the appearance of your oil and coolant. Is the oil milky? Coolant oily? Either could be indicative of a head gasket leak. Or potentially cracked head I suppose. After checking fluids I would use a pressure tester on the cooling system. Top off the coolant (you can just add water for testing if it is empty), pump up the pressure and look for leaks. Usually the cause is an obvious leak in stealth mode.

https://www.amazon.com/gp/product/B0002SRGWU/?tag=wranglerorg-20

so i've done two oil changes since this started expecting to see the milkshake kinda mess but it was surprisingly clean both times and nothing looked abnormal.
i guess a pressure tester is the next step.

 

[Flivver250]

That is good news.

 

[TJ4Jim]

Pull the plugs and look at the condition of each, a nice clean plug can be evidence of a coolant leak into a cylinder.

 

[4speedhandler]

Pull the plugs and look at the condition of each, a nice clean plug can be evidence of a coolant leak into a cylinder.

i'll add it to the list of diagnostic tests

 

[Lou]

What year is your jeep?

 

[4speedhandler]

What year is your jeep?

its a 2000 sahara with the 4L 5 speed combo

 

[Lou]

https://www.amazon.com/dp/B0007ZDRUI/?tag=wranglerorg-20

 

[4speedhandler]

https://www.amazon.com/dp/B0007ZDRUI/?tag=wranglerorg-20

thats pretty cool i had not seen that before. im going to order one up

 

[B34C0N]

https://www.amazon.com/dp/B0007ZDRUI/?tag=wranglerorg-20

I actually just ordered that. The CA Heat wave had my Jeep overheating really bad. And I found gunk in my radiator.