TL;DR;

People have said coolant in the transmission will destroy the tranny fast. Like how fast? Like will it destroy the transmission even if I am not driving it? Can I drive it 20 or 30 miles to a friends to fix it there (I don't have garage)?

The coolant I see in my 2000 XJ radiator is a nasty red-ish color, but all of the coolant in the reservoir is still green.

Green coolant




I checked again this morning and now I am second guessing if there is actually coolant on the dipstick. Anyone have a good way to tell what this junk is that is dirtying up my coolant?

So I bought the car two months ago. Auto trans, 4L I6 engine with 164K. The guy I bought it from had a stack receipts of the work he had done. Unfortunately I didn't take a closer look at them until after I bought the car . Anyway, I noticed he replaced the thermostat and flushed the coolant about 8 months before I bought it, and then replaced the thermostat and flushed again about 1 month before I bought it. So thats 6-7 months between flushes and tstats being replaced, which seems sketchy that it would be done so close together.

Anyway, all of that may have nothing to do with my current problem, but I figured the more information the better, as I am not super mechanical.

Obviously when I bought the car, the coolant in the reservoir was nice and green since it had just been flushed. I took the rad cap off and the coolant was nice and green there also. When I checked both the reservoir and the radiator a couple of weeks later, everything still looked good. Fast-forward about a month and half. Drove to a friends house, and when I came out, there was a liquid stain (around the size of a frisbee) on the driveway close to the driver side tire. After taking a paper towel to the stain it almost looked like coolant mixed with tranny fluid. I didn't know how that would happened, so I just thought I was crazy and just assumed it was a coolant leak. I cleaned up all the coolant I could from under the hood and drove back home (there was plenty good looking green coolant in the reservoir). When I got home, I tried to find the leak, and it had stopped leaking. That was two days ago. I drove to the store and back today to see if I could get the leak again, with no luck. So I popped the radiator cap, and sure enough, it is no longer a healthy green color. It has a redish hue to it. I will try to take a picture of it tomorrow. After doing some reading in the forums, I checked my transmission fluid (with the car off, not sure if that matters since I am not checking the level) and I can't tell for sure, but it seems there is coolant mixed with the tranny fluid on the dipstick.

I am not positive, but from what I have read, it seems something has gone wrong with the transmission cooler inside the radiator and I think I need to replace the radiator and the flush both the coolant system and the transmission. Does that sound right?

People have said coolant in the transmission will destroy the tranny fast. Like how fast? Like will it destroy the transmission even if I am not driving it? Can I drive it 20 or 30 miles to a friends to fix it there (I don't have garage)?

And forgive my last question if it is totally a n00b one, but I have heard something along the lines of, you should not flush an old transmission if it has not been flushed before. Something about all the crap inside can get knocked loose and make things worse. I have no idea if/when my transmission was flushed last, so is this something I should be concerned about, or I am understanding that all wrong?

Also, since noticing the puddle, I have been keeping an eye on my engine temp and the temp randomly will drop from 210 to below 100. Probably unrelated to the above problem (probably something wrong with the temp sensor/wiring), but I thought it was worth mentioning.

 

I don't think it'll hurt anything sitting for a week or two but I wouldn't want to drive 30 miles with any significant coolant in the trans fluid.

Edit: I wasn't able to see the pics last night. That looks like a combo of stop-leak and rust. That's what my cooling system looked like (but worse) when the radiator pooped the bed and moved the cooling system refresh up on the list. I replaced everything (radiator, heater core, water pump, water neck, thermostat, radiator & heater hoses, & coolant recovery tank). Still had to flush a lot of crap out of the block.

 

First, it looks like the coolant in your reservoir is never making it into the radiator. Otherwise, your radiator coolant level wouldn't be low as you show in the pictures. The coolant should be at the top of the radiator fill neck at all times if there is a proper level in the reservoir. Check for clogs in the hose to the reservoir. Disconnect and blow through it.

It's hard to tell what is going on since your radiator is low. The reddish tint of your radiator could be from rust or trans fluid. Your trans fluid is brown rather than red, but to me it doesn't necessarily appear to have coolant in it. Due to the brown color though, I would change it immediately, especially if you're going to drive it (I wouldn't). Usually trans fluid in the coolant or vice-versa will be foamy or creamy-looking, but your trans fluid looks translucent. Coolant with trans fluid introduced will often look like Pepto-Bismol.

I probably would fill the radiator, and run it a while parked at full temp to see what the coolant really looks like.

 

With mine looking like yours, the previous owner added heater core stop leak which changed the color to look like yours and ended up clogging my heater core. I had to replace my heather core as a result, which is a pain in the rear!!

 

​​​​​Is there anyway to, specifically check that the heater core is clogged (without just replacing it lol) ? I have heard that if the heat isn't working in the car it could be your heater core, but it could also be other things (low coolant etc).

 

Flush water through it.

 

Flush the heater core.

IMHO, the easiest way is to disconnect the heater hoses at the water neck. That allows you to direct one into a bucket to catch coolant and flush through the other. Once you're dealing with just water, flush it in both directions repeatedly. Be careful how much pressure you use. City water pressure can be enough to damage your heater core (cause a leak).

That said, flush the entire system. Disconnect the lower radiator hose, and the upper at the water neck. It helps to remove the thermostat as well to increase water flow. Catch the coolant from the lower hose, and then flush every which way until everything comes out clean. It may take several flushes and/or using a flush chemical or cleaner. Lots to be found via Google on those topics.

 

So I opened the radiator and filled it with the engine running. As the engine warmed up, the radiator started to overflow a bit, so I put the radiator cap back on, then turned the car off.
​​ I let it sit for a a few minutes and when I tried to take the cap off again, coolant was erupting out the sides. It's not sludgy really, it's clear like coolant, just not green like coolant.


As for the transmission flush, will it hurt anything in the transmission if it has never been flushed before? I don't know if I have to tools or know how to do a flush myself. Can any mechanic shop do this? I just moved so I don't really know what mechanics around are reputable or not.

When I get the trans flushed and can find a work space to flush the coolant and replace the hoses I will. But doesn't it seem weird that the tstat, hoses and coolant were replaced twice in less than a year?? Especially a month before the PO sold it (sigh)... There has gotta be something wrong with the cooling system that causes it to keep clogging, right?

Thanks for all the input so far from everyone.

 

If the cooling system was seriously neglected, it takes repeated flushes to get all of the crap out - especially if there is something like stop leak added to the mix. A "standard" flush 8 months ago, and then another 6 months later could easily leave you with the mess that you have.

 

"So I opened the radiator and filled it with the engine running. As the engine warmed up, the radiator started to overflow a bit, so I put the radiator cap back on, then turned the car off.
​​ I let it sit for a a few minutes and when I tried to take the cap off again, coolant was erupting out the sides. It's not sludgy really, it's clear like coolant, just not green like coolant."

The system will be under pressure. You still need to find out why it didn't go to the reservoir.

 

Let the coolant circulate for a while with the coolant topped off, radiator cap on and engine running at full temp. You won't know what it really looks like until you do this--the new coolant mix will just sit on top until it circulates a while. Allow the engine to cool down, then take the cap off and have a look. Don't forget to check the overflow hose as I mentioned before.


No, a flush/fill won't hurt, but a drain/fill would be gentler. If your fluid has particles in it and looks/smells burnt, then you may have some issues after a flush, but from what I can see in your pic, it doesn't look bad, just old and used. I wouldn't hesitate to have the fluid replaced, but honestly I would just drain and replace the fluid from the pan (drain plug) myself 3-4 times. Let it run and circulate between each r&r. Pour in the exact quantity of fluid that you drain out each time, and check the level at operating temperature with the engine running and trans in park.

There's no need to overthink this at this point, IMO. Everything I've seen indicates to me that the cooling system has been neglected and the PO tried to "make it right" before it was sold. I have seen nothing that would prove to me that you have a coolant<>transmission fluid leak. Refresh the trans fluid, flush the hell out of the cooling system and then re-analyze. It does appear from your pics that reddish coolant has spewed out of the radiator cap at some point. The evidence is on the black plastic in that area, such as the air filter box and power steering reservoir. This could have been caused by a clogged overflow. Replace the radiator cap (16lb) while you're at it.

You need to find the leak as well. I wouldn't be surprised if outdoorsavvy85 is correct--that the PO poured stop leak to plug up a leak that he didn't want to fix before he sold it.

 

So.... I found the clog in the reservoir hose.

Things that make you go... HmmmmI felt a lump in the hose so I replaced it. I cut the old one open and ^ that's what I got. Does this mean my engine is on its last leg?

Also here is an updated picture of the coolant.


So the big sneeze of coolant I noticed before was by my driver side tire, any idea where to start looking for the leak?

 

Flush the hell out of the cooling system.

Then borrow a combustion leak tester from your local auto parts store and test for an exhaust leak into the coolant.

If you don't think you should do that, search for "0331 head crack," read up on it and see if that changes your mind.

 

So I plan on flushing the coolant and then draining and filling the transmission. My old floor jack isn't tall enough to lift the jeep, so I need to get a bigger one, but I am broke as a joke at the moment. Is it going to be a nightmare trying to do the coolant flush and/or the tranny drain and fill without lifting the car?

 

You sure did! It doesn't say anything about your engine, per se, but it does show that your cooling system needs TLC.

^ Good advice here.

Nope. You don't need to lift to do any of it. When you drain the trans, use a funnel into a jug that you can measure from. I use a 1-gallon oil jug that has the quart marks on the side, so I know how much I've drained out and need to put back in. The funnel should allow you to get to the drain plug, which is partially obstructed by the transmission cross-member.

However, concentrate on the cooling system first. Your transmission fluid doesn't really appear to have an issue, it is just in need of maintenance. The cooling system issue is more important right now. Be sure to watch that "superflush" video that was posted earlier in this thread.