XJ coolant overflow after engine is shut off

[JMA_2001XJ]

Have you assessed whether there is any correlation to the kinds of driving being done before parking? Or whether it correlates to parking over a cooler area (garage) or over hot asphalt? Have you check the boiling point of your coolant? I guess you still haven't tried a different cap?

No correlation. I drive pretty consistent. Not aggressive at all, this is not the vehicle for that. It has only happened over asphalt. Still no new cap because the system was showing a lack of being able to hold pressure when the test cap with gauge was on. The cap was replaced 6 months ago with an OEM one.

 

[JMA_2001XJ]

I had the same issue in NY in the summer a few years ago, I replaced the fan clutch and it solved the issue. Even though it spins it doesn't mean it's okay.

The mechanical fan works as it should.

 

[rtolboom]

The cooling liquid is not circulating after you turn off the engine. Could it be that the liquid starts to boiling because of the hot engine? The question is - why is it boiling? I have watched the one of the Youtube video's of Chris Fix. He shows that water starts boiling at a lower temperature than a mixture of ethylene glycol and water. Could it be that there is too much water in your mixture?

 

[rtolboom]

here is the video, see 01:25: https://www.youtube.com/watch?v=29z94xBdAjE

 

[maxbraketorque]

The cooling liquid is not circulating after you turn off the engine. Could it be that the liquid starts to boiling because of the hot engine? The question is - why is it boiling? I have watched the one of the Youtube video's of Chris Fix. He shows that water starts boiling at a lower temperature than a mixture of ethylene glycol and water. Could it be that there is too much water in your mixture?

I don't think there is any magic about still coolant boiling below its rated boiling point. Water can boil after shutdown if a large fraction of the engine block is sitting at a temperature significantly above the boiling temperature of the coolant. And the 4L block has a lot of iron that can be toasty, especially around the exhaust passages. I could imagine that heat could flow from the exhaust manifold into the head.

 

[XJI6191]

(1) a function of anti-freeze is to raise the boiling point of the coolant above 212*
(2) temperature of coolant increases when the engine is turned off, because there is no airflow thru' the rad. (which is why some electric fans are designed to continue running after the car stops, indeed some have been known to cut in after the car's parked & the driver is walking away)

 

[rtolboom]

Thank you all for your answers! I realized that I diluted the pre-mixed coolant with water so I asked chatgpt if this could caused the high pressure. This is what the AI said when I asked about water only versus water/glycol (50/50):

The pressure in a closed cooling system of a car will be higher when only water is used compared to a typical glycol/water mixture. This is due to the different physical properties of water and glycol/water mixtures.

Key Points to Consider:​

1. Boiling Point:
   • Water: The boiling point of pure water is 100°C at atmospheric pressure. In a closed system, the boiling point can be higher due to the increased pressure, but it will still be lower than a mixture with glycol.
   • Glycol/Water Mixture: A glycol (such as ethylene glycol) and water mixture has a higher boiling point. For example, a mixture of 50% ethylene glycol and 50% water has a boiling point of about 107-110°C at atmospheric pressure.
2. Pressure Development:
   • Because water has a lower boiling point, it will evaporate more quickly at a lower temperature compared to a glycol/water mixture. This leads to a higher pressure buildup in the system.
   • A glycol/water mixture can reach higher temperatures before it starts to boil, resulting in slower pressure increase under similar conditions.
3. Heat Transfer:
   • Water has a higher heat capacity than glycol, meaning it is more efficient at transferring heat. However, because water boils faster, this can lead to vapor formation and thus a higher pressure buildup.

Practical Implications:​

• Higher Pressure: Using pure water can lead to higher pressure in the cooling system at the same operating temperatures because water boils faster and becomes vapor.
• Cooling Efficiency: While water is an excellent coolant due to its high specific heat, the boiling point-raising properties of glycol are essential to prevent overheating and excessive pressure buildup.

Conclusion:​

Yes, the pressure in a closed cooling system will be higher if pure water is used instead of a glycol/water mixture. Therefore, a glycol/water mixture is typically used in car cooling systems to take advantage of the boiling point elevation and to keep the pressure under control.

 

[lawsoncl]

A 180 thermostat does not magically make a marginal cooling system work better. I suspect those claiming it solved their problem simply replaced a bad thermostat with a work one.

An incorrect glycol mix can indeed cause boil-over.

 

[Tim_MN]

Assuming a proper 50/50 mix of coolant and water, boiling coolant after engine shut-off is not due to the thermostat temperature rating, the root cause is weak or defective cooling system components. Excessive build-up of scale in the block, or the radiator, is a cooling efficiency defect that should be addressed.

 

[dktool]

OP, post back after confirming FOR SURE whether or not the system passes a pressure test.

 

[RCP Phx]

OP, post back after confirming FOR SURE whether or not the system passes a pressure test.

He hasn't been back since October !!!

 

[89Mock]

He came back June 20.
My guess is him diluting 50/50 coolant caused his problems, and when he figured out he was diluting pre mix he drained the coolant, refilled with proper coolant mixtures, and his issue went away.

 

[Saudade]

Who came back? The OP is not the same as the one stating the dilution of the 50/50. At least, that statement is not quoted followed by the bot response.

Hopefully the OP got it sorted out. Yes, would be nice to "close out" the thread but not everyone does it.