The PO might've tried to remove the old drain plug housing. If you twist the black plastic nut that the blue drain plug settles in to, most times you still get the plastic pieces farther up left behind, so it would just look like a hole. Usually leads to a pretty slow leak. Those plastic parts that get left behind have O rings that seal to the shaft, so if you had a slight leak, that's probably what it was.

 

Some of the replacement radiators do not have the drain plug. Sad, but true.

 

I'm having a similar issue - just finished doing the full radiator swap, taking out and replacing the aluminum grille, the expansion tank, the lower and upper radiator hoses, the Thermostat for the transmission cooler, the O-Ring for the lower radiator hose's temperature sensor plug/thingie.

I got a TYC Genera replacement radiator (#2636) installed in my '01 325i (auto transmission) and after a few hours of hard wrenching, everything is in. So imagine my frustration then as I move under to finish up the job and tighten the plug and pour in some brand new German antifreeze, only to find that the OEM blue coolant tank drain plug doesn't fit! I'll include more pictures later but essentially the OEM blue plug is too "loose" inside the black plastic housing on the bottom of expansion tank that looks like a giant plastic castle nut. I'm not quite sure what I'm supposed to do - the radiator came with the peacock/radiator adjustment valve thing, but without the replacement blue drain plug. Anyone who has used the TYC radiator know what the diameter of their drain plug hole is? I purchased this off ebay in the meantime:


17 11 1 707 818


Will give an update once the part has arrived and I can give a proper reading with the digital calipers. I'm hoping its as simple as me taking the new drain plug, pushing it in and I can screw it in perfectly flush. If not, any advice would be appreciated (including a suitable DIY alternative drain plug solution). :ben:

 

Belts are wet? So what?

Belts get wet in the rain. This is a zero on a scale of 1 to 10.

 

UPDATE: Okay, so apparently after calling TYC Genera's west coast distribution center, the customer service rep looked up my part (#2636) and confirmed that that black plastic castle nut thingie is actually the new drain plug itself, and I could dispose of the old blue OEM one. He told me TYC Genera did it so parts can be universally interchangeable between different model years, trims and transmission setups, thus keeping costs down for the company (and therefore the consumer). I'm not going to take him completely on his word just yet till I get home and try pouring some anti freeze and running a full bleed. If there are no leak spots from the plug area on the white cardboard I placed under the car, I am in the clear. Will let you all know how it works out and will include pictures for better explanations.

So lesson: Call your part manufacturer to confirm any changes to the OEM design on the replacement part you are trying to install.

 

Only Modine radiators have the blue drain plug.
Nissens has very similar or same design, but theirs is black. Behr has a larger size black plug with a hex head, so its removed or installed by a hex socket and wrench, not by a Philips screw driver.

I have never heard of TYC Genera radiators before - found them on Bavauto's website - they look like rebranded Nissens to me. If your radiator has a black drain plug with a Philips type head, most likely it is a rebranded Nissens. In this case the black and the blue plugs are interchangeable.

 

Only Modine radiators have the blue drain plug.
Nissens has very similar or same design, but theirs is black. Behr has a larger size black plug with a hex head, so its removed or installed by a hex socket and wrench, not by a Philips screw driver.

Finally! Someone synthesised all the information out there and put it in one concise statement!

There's nearly as many "my radiator doesn't have a drain plug" threads as there are " what oil to use" threads! Well, not quite but you know.....

 

I have a new behr / mahle and it has the black hex nut as well

Learn something new!