Oil in Coolant Tank '06 Pacifica
 

Hey guys. Question here. I have a 2006 Pacifica Touring 3.5L. Last summer I noticed 'milkshaky' looking stuff coming out of the coolant tank. I brought it in and they said was engine oil cooler, so they changed it. All was fine until a month ago when I noticed a puddle of the 'goo' under the car again. They tried a new oil cooler just to be sure but same issue. I just did a block tester and the liquid stayed Blue. I ran the car for at least 10-15 mins and still stayed Blue entire time. Just to be sure I tested the liquid by the exhaust pipe and turned Yellow immediately. So unless I'm missing something, it's not a head gasket/crack etc...The car doesn't have a radiator cap so I did the test in the coolant tank. Any other ideas as to what could be causing oil to get into the coolant tank? Much appreciated!

It can only happen from a fault in the head gasket, block or cylinder head!

So then the block tester is inaccurate?

Unless someone is pouring motor oil into the coolant reservoir!

One last possibility, Leaking gasket for the water pump/ timing belt cover area. From what I understand, there are 4 o ring seals involved.

Bypass the radiator engine oil cooler, flush the cooling system see if the problem goes away. Oil pressure is higher than coolant so that is the most likely cause.
Other chance is that there is a head, block or head gasket problem. Oil supply for the rockers travels thru a head bolt cavity in the block, up thru the head (and gasket) to the rockers. Could cause oil in coolant without a combustion leak hence the result with the block test fluid.
Bypassing the cooler cheap and easy. You can just plug the lines as it is a by pass cooler not a full flow cooler.

I have a 2005 Chrysler Pacifica w/ 3.5L. Had a coolant leak in the side of the aluminum block 2 years ago, leak caused by thin casting and corrosion. Used Blue Devil Block Sealer, it sealed the leak up tight! Has not leaked since. The Blue Devil stuff is quite good, by buddy uses it in his shop with great results.
It could be worth considering considering the residual value of our Pacs and the high effort in repairing 'em.