Sudden High Idle and Frothy coolant in engine bay.

Good morning to everyone out there. I purchased a 2000 XJ with a 4.0L I6 and 143,000 miles about 2 months ago and have been having a lot of fun with it so far, but I ran into an issue that I wanted to get some advice on and hopefully someone can educate me on why my XJ did what it did.

About a three days ago, (at 149,500 miles) I was performing general maintenance, changed the oil, new H4 headlight bulbs etc and noticed I had a significant amount of rust in my coolant. So I went online and ordered some Gunk heavy duty coolant flush, with rust treatment which I have linked below.

https://www.amazon.com/Gunk-C2124-Super-Heavty-Radiator/dp/B00200SBAY

I followed directions and did 2 flushes with this product, followed by flushing the radiator, heater core and motor with distilled water until each ran clear, then I refilled with coolant, burped the system for about 5 minutes with a no spill funnel and everything appeared perfect.


This morning, right at about 150k miles, I started up my XJ to go to work and about a mile down the road, the idle kicked up to about 1,000 rpms and it sounded like I had a fan that was spinning ultra fast. As I pushed the gas the rpms seemed to rise higher than usual for the pressure applied. The fan type noise was loud enough for me to take concern so I pulled over, shut off the engine and found what appears to be frothy coolant on an electrical connection behind the heater hoses on the passenger side near my firewall.

Click here for Linked Image.


Sorry about the quality.

The heater hoses dont seem to be leaking, so I'm guessing the coolant came from the wand tube shown, but that's speculation...

Up to this point, my temperature was normal and steady, I have no CEL and when I restarted the XJ to see if I could find where the coolant was coming from, it ran normally and didn't seem to be coming out anywhere. I let it idle for about 5 minutes and it all seemed normal, so I continued my 40 minute drive to work. The remainder of the drive, I didn't have another rpm issue, it never went over normal temps and didn't have coolant in that area after I parked.

Any ideas or suggestions here? Did I just not flush the engine with distilled water well enough? Could that cause pressure to force a little frothy coolant out?

Thank you all in advance.

Engine speed is controlled by air+gas flow. The cooling system isn't directly connected to either of those, but its possible that coolant spillage caused something else to go haywire (unlikely but possible). Best advice I can give is clean the engine bay and wait for it to happen again.

Check the transmission fluid! If the foamy coolant came out of the tranny dipstick, then you're looking at a tranny cooler leak inside the radiator. Coolant in the trans fluid can severely damage the clutches.