1lowtc

Hey everyone,

I'm having a problem with my 08 RDX tech. Just the other day I was driving home with no problems, parked the car in the driveway and come out to a puddle of liquid dried up. I pull into the garage and see that it is red liquid, first thought was transmission fluid. Upon further inspection, I found it was the coolant leaking from the cap of the overflow when the car started to warm up.

Now, the tank is completely full to the brim with red liquid, I open up the radiator cap and the pressure releases and the radiator is full to the brim and constantly filling up due to the overflow being full.

What can cause this problem?

I was reading up on different forums of other cars having similar symptoms and they were saying its the head gasket.

I really hope its not the head gasket. Has anyone ever replaced theirs?

Thank you for the help.

Tomtwtwtw

If it was your head gasket, it wouldn't be leaking from your cap, it would go into the exhaust. The only way it should leak from the cap on the overflow tank is if the cap is bad - look at replacing that first. I've had one go bad on a previous car - when it goes bad, the system doesn't hold pressure. When the system doesn't hold pressure, the coolant boils. When the coolant boils, it goes out the bad cap. New cap should be very cheap, so do that first and go from there.

1lowtc

Ok, so I should change the overflow tank cap? Or just change both, overflow amd rad cap?

Also, why is the coolant red like ATF? That was my first thought that I had a tranny leak from somewhere.

mrgold35

I've had two old Honda Accords that had bad radiator caps after +100,000 miles. Just normal wear/tear. Once the cap failed completely and coolant was boiling out around the cap. Without proper pressure, the coolant will boil, expand, overflow and evaporate out. If it was a head gasket, you would see chocolate milk looking oil on the dipstick and/or white-ish smoke out the exhaust that smell like antifreeze at worst.

Tomtwtwtw

Change which ever cap it's leaking from - most likely this is the cap on the expansion / overflow tank, not on the radiator itself. If you still have issues after that, consider doing a pressure-test on the cooling system.

1lowtc

Thanks for the help... I will let you know what happens.

1lowtc

Hey guys I was talking to my mechanics and 2 said it is the head gasket and the other said it is the radiator. Does the tranny fluid flow through the radiator or is there a separate tranny cooler? He was saying that a baffle must have broke and the fluid is mixing with the coolant making the coolant as red as ATF.

Does that sound right?

Tomtwtwtw

So I still don't believe your head gasket is the issue, as DC said that would show in the exhaust and not the ground. However I do believe most automatics do have a transmission cooler integrated into the radiator. Never heard of it breaking internally and allowing coolant and fluid to mix, but if that is indeed the case, I'd be more worried about coolant being mixed with your transmission fluid - that does not provide the lubrication necessary and could screw up the tranny. I don't recommend driving until that can be ruled out or fixed.

An alternative reason for your coolant being red is that it may have been flushed by the previous owner and replaced with red coolant instead of OEM (which I think is blue for Hondas...some correct me if wrong). Many aftermarket coolants claim to be compatible with all manufacturers, and colors can vary as they're usually just dyes and have nothing to do with the actual chemical compounds.

1lowtc

Yea I am not driving it at all... I will be getting it towed to the shop to fix it tomorrow. He was so sure that it is the radiator... Right now that is the cheaper option to start with... I'm not saying I wanna go cheap to fix it but I also don't want to spend over $2000 to fix the head gasket.

mrgold35

I thought the RDX has a separate smaller trans cooler located in-front of the radiator and condenser. I'm not 100% sure; but, I thought it was a direct connect to the 5AT bypassing the radiator fluid to help cool the 5AT down. You should be able to see the small radiator if you peek into the front grille. Some trans coolers are just a metal loop inside the radiator (like in sedan/coups) and that is where I think the mechanic is thinking how the RDX is configured.

It would be the same thing as the bad engine head gasket if you check the 5AT dipstick; is the 5AT clear red (or brownish red if the 5AT oil is getting old) OR milky red? I don't think you will find milky red fluid.

Some antifreeze come in a red-ish color compared to the traditional lime green. Maybe the fluid was changed way back then to explain the color? I think double-checking the radiator cap and/or overflow tank cap would be first.

Tomtwtwtw

So, if it were me, I'd first do what I can to rule out any possibility that there is tranny fluid and coolant mixing in the radiator. If as DC said they are separate units, then you have no worries. (and car is ok to drive as long as you don't let it overheat)

Assuming that checks out, spend the 10 bucks and get a new overflow cap since you said it was coming out from there. That means the cap is definitely bad - maybe not the only thing, but at least one thing, and it's cheap to replace. Pop new cap on, fill and bleed system, and test drive.

If still issues after that, maybe try a pressure test to see if it is leaking from anywhere else (radiator crack, worn hose, etc). There are other signs that indicate a head gasket - check those as well before you plop $$$ down (coolant in oil, coolant out exhaust, etc)

1lowtc

Ok I'll have it all checked tomorrow... I don't have the time to do all the work so I will have my mechanic do it.

Also, when I checked the level of the tranny fluid on the dipstick, there was no fluid on it, I pulled it out and cleaned it off then put it back in and checked again and the only fluid on it was remnants of inside the tube. The tip had nothing on it at all.

So, I won't be driving it lol.

protoRDX

Ok, you ve got a very bad situation. The problem is that we have an ATF cooling line inside our main radiator. Two necks (in and out) to which atf hoses are attached tend to get rusty and at one point your atf is going into main radiator and coolant is going inside your tranny.
You absolutely must stop driving your car and tow it to the nearest garage.
The very least damage would be just a new radiator.
But if you already had red fluid inside your overflow and you kept driving it means you basically killed you tranny. Means you might need to perform an entire tranny rebuild procedure.

We had several threads about this issue here.

1lowtc

I stopped driving it immediately Friday when it started. I have a new radiator coming in today and getting replaced today. It is getting towed also not being driven.

fake_usa

did the cap fix your leak?

1lowtc

No it was not the cap... I had to get the radiator replaced... Once the radiator was removed the connection on the radiator for the transmission line fell right out. It was broken at the bottom and fluid was mixing with the coolant.

Had a complete flush and everything is great now.