Transmission fluid in radiator - Coolant inside the transmission?

The only reason is the transmission cooler on the radiator is leaking into the radiator and that's how your getting the transmission fluid into the coolant.I would replace the radiator and flush the cooling system real good and hope for the best. These guides will help fix it step by step.

https://www.2carpros.com/articles/how-to-replace-a-car-radiator

and

https://www.2carpros.com/articles/how-to-service-an-automatic-transmission

Please run down these guides and report back.

Welcome to 2CarPros. Your description sounds like the transmission cooler in the radiator has failed and is leaking. The problem with this is that coolant in the transmission will glaze the friction surfaces in the transmission. The best way to deal with that would be to rebuild the transmission and replace the torque converter as that would get the contaminated fluid out of the entire unit and the friction surfaces will be new. I know of nothing that would flush the coolant out of the friction surfaces well enough to trust them.

You will need to replace the radiator with a new one but, before you do that you will also need to deal with the contaminated coolant and engine. For that you can start by draining the system, blocking off the transmission cooler ports and connect the two transmission lines together to keep from leaking fluids all over. Now fill the radiator with clean water with a bit of classic Dawn dish detergent in it. Run that through it for about 5 minutes, then let it set a bit and run it again. Now drain that out and repeat until the water looks clear. That will clean the oil and crud out of the cooling system and hopefully the heater core. At this point you can drain the system, then replace the radiator and all of the hoses that had the oil/coolant mix in the. The oil and detergents in the transmission fluid will attack the rubber they are made from and they will fail. Better to replace them before that happens. Replace the thermostat as well.

Your vehicle is equipped with a transmission cooler which shares the same coolant as the engine to help keep the automatic transmission assembly cooled off. There is a fault with the tranny cooler, cooler line or tranny itself causing the tranny fluid to leak into the cooling system.

Change the radiator the tank is cracked.

Look at the bottom of radiator the lines should connect there.

Here's a diagram.

Fluid Condition
Along with fluid level, it is important to check the condition of the fluid. When the fluid smells burned, and is contaminated with metal or friction material particles, a complete transaxle recondition is probably required. Be sure to examine the fluid on the dipstick closely. If there is any doubt about its condition, drain out a sample for a double check. Mopar ATF+4 (Automatic Transmission Fluid) when new is red in color. The ATF is dyed red so it can be identified from other fluids used in the vehicle such as engine oil or antifreeze. The red color is not permanent and is not an indicator of fluid condition. As the vehicle is driven, the ATF will begin to look darker in color and may eventually become brown. This is normal. ATF+4 also has a unique odor that may change with age. Consequently, odor and color cannot be used to indicate the fluid condition or the need for a fluid change. After the fluid has been checked, seat the dipstick fully to seal out water and dirt. OIL COOLER FLUSHING

NOTE: Manufacturer recommends Cooler Flusher (6906) as the only suitable procedure for flushing oil cooler. Use only petroleum-based flushing solvents. Do not use solvents containing acids, water, gasoline or any other corrosive liquids.
NOTE: Always reverse flush when flushing oil cooler and lines.

Flushing Procedure
1. Note oil cooler supply and return lines. See Fig. 6. Remove cover plate filler plug on cooler flusher. Fill reservoir 1/2 to 3/4 full of fresh flushing solution. 2. Reinstall filler plug. Ensure pump power switch is in OFF position. Connect Red alligator clip to battery positive, and Black alligator clip to chassis ground. Disconnect oil cooler lines at transaxle. 3. Connect Blue pressure line to outlet oil cooler line. Connect Clear return line to inlet oil cooler line. Turn pump on and flush oil cooler and lines for 3 minutes. 4. Monitor pressure reading and Clear return line. Check equipment manufacturers instructions for pressure specifications. If solvent flow is intermittent or exceeds specified pressure, replace oil cooler(s). 5. Turn pump off. Disconnect Clear suction line from reservoir at cover plate. Turn pump on for 30 seconds to purge flushing solution from oil cooler lines. Turn pump off. 6. Place Clear suction line into a one qt. (.95L) container filled with ATF. Turn pump on until all fluid is removed from container. This removes remaining flushing solvent from oil cooler lines. Turn pump off. 7. Disconnect alligator clips from battery and ground. Remove flushing adapters from oil cooler lines. Reconnect oil cooler lines. Fill transaxle with appropriate fluid to proper level. See CHECKING FLUID LEVELS.
Fig. 6: Identifying Transaxle Oil Cooler Lines
Courtesy of DAIMLERCHRYSLER CORPORATION
OIL COOLER FLOW CHECK
1. With transaxle fluid filled to proper level, disconnect oil cooler return line at transaxle. See Fig. 6. Place container under oil cooler return line.

CAUTION:Do not obtain more than one quart of fluid, or transaxle may be damaged.
2. Apply parking brake. Start engine and allow it to idle. Place gearshift lever in Neutral. Check fluid flow from oil cooler return line. 3. If fluid flow is consistent and takes 20 seconds or less to obtain one quart, oil pump volume and oil cooler flow are okay. If fluid flow is intermittent or takes more than 20 seconds to obtain one quart, disconnect oil cooler inlet line. Refill transaxle to proper level and recheck flow. 4. If fluid flow is intermittent or takes more than 20 seconds to obtain one quart, check line pressure. See PERFORMANCE TESTS in appropriate DIAGNOSIS article. If fluid flow is consistent and takes 20 seconds or less to obtain one quart, replace oil cooler. Reconnect oil cooler lines. Fill transaxle with appropriate fluid to proper level. See CHECKING FLUID LEVELS.

Could be the oil cooler for the tranny at the radiator leaking internally.

Replace the radiator the tranny fluid gots no business mixing with coolant-

Yes it can. I actually got a neon with this problem and fixed it and sold to a friend and its been 2 yrs now. Best thiong to do it take it to a transmission shop and have them flush the system. The difference between a flush and just changing the oil and filter is a flush gets all the old fluid out and the filter and gasket only gets out a third of the old oil.

No sir. This is a 1 hundred dollar job

Hi there,

if this happens, you really have to catch it straight away, because if the trans oil is contaminated with water, it will get in to the valve body and the torque converter and even if you flush the trans you never get rid of all the moisture and corrosion and valve problems will plague you always.

Mark (mhpautos)