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sprinkles08, ASE Certified Technician
Category: Car
Satisfied Customers: 23115
Experience:  ASE Master and Advanced level certified. Factory trained with 17 years dealership experience
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Mazda Millenia: Overheating and plug issue

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Hello, I have a 99 Millenia that overheated and wont hold antifreeze in the radiator. After inspecting it last night we noticed a rubber plug that was cracked on the bottom left hand corner of the radiator. It makes no sense to have a plug on a radiator as it seems it would restrict airflow. Its blew every hose and it seems this would be the issue. Am I right and is there a hose that belongs there or do I need to replace this plug? Thanks, Joel

Hello and welcome to JustAnswer!

Is the coolant actually leaking from the cracked plug that you found? If it's coming from the plug then that's definitely your issue. The location you described sounds like it could be the radiator drain plug or a plug that was put in place to block an unused port on the radiator. For instance with many aftermarket radiators there are sometimes unused fittings for other heater hose configurations and rubber plugs are used to seal these fittings.

If coolant is leaking from the plug then you'll definitely need to attempt to replace it. If you are unsure what it is or how to go about replacing it, uploading a picture of it here would be extremely helpful.
Customer: replied 4 years ago.

Im sorry there was a cracked rubber cap with a hose clamp around it that was directly behind the oil filter on the engine block. Is this factory and does it just need replaced or is there a hose that should be there? Yes as soon as you poor anti freeze or water it leaks directly out of this nipple.

That sounds like it may have been a fitting for an something like an engine oil cooler and it wasn't being used. The cap you're describing there is going to be exactly the same thing I was envisioning at the radiator. They simply slide over the fitting and are clamped on. Any parts store will have these in stock in multiple sizes. You'll want to try to remove the old one leaving it intact as possible and then you can take it along to the parts store to match up the size.

Here is a link showing the type of cap I believe you have.
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Customer: replied 4 years ago.

Yes this is the hose I was refering to. Thanks for the link and your help. Ill go pick up another cap tomorrow and replace it and hopefully this is the last of the overheating issues that Ive been having. The cap didnt seem dry rotted like the hoses that I had to replace though. Ive also replaced the thermostat and the radiator looks to be in great shape so Im kinda puzzled on how this cap also cracked.

It may just be cracked from heat and age. It would be under quite a bit of heat from the coolant, engine block, and underhood heat. Add that to the pressure it's always under and hopefully it just failed from age.