I have a pretty significant coolant leak and I'm confused at this point as to where it's coming from. I did a little test drive the other day after installing my block off plates and it was heating up much quicker than normal. Due to construction and the angle of my driveway (Unless I pull in at a certain angle I scrape my exhaust), I need to pull a U and back up my street and pull up my driveway. When I stopped backing up and headed up my driveway, it left a solid trail of coolant from the street to my garage. I parked and looked under and no heavy dripping. Drips, but not anything obviously major. After letting it sit for a few days I looked in the rad and it seemed basically empty. But no huge puddle under the car.

Tonight I filled it up completely and went for an hour drive. It ran cool the entire time with no issues. But after the backup, stop, and up the driveway I had a solid trail of coolant again.

I checked the main rad hoses, heater hose, coolant hose under the UIM, BAC line, turbo line, rad plug, etc. and all appear fine. I recently cleaned the block off and there are no visable signs of a leak anywhere. Looking under the car, the only place it seems to be leaking from is above the metal shield/tray under the transmission, more on the pass side behind the turbo. When I look from above, the trans and whole side of the engine is completely dry. There is also usually a little puddle of coolant in the cradle where the LIM meets the engine block.

Sorry this was so long, but it's a mystery to me. And I know one of you out there has an answer to this. The best I can come up with is something is leaking slow and puddling on the plastic undertray or metal shield, and then pouring out after reverse, stop, and forward. Thanks in advance for any advice you have.

 

Yeah, I was going to say take your undertray off then do that again.

I also thing that you can purchase a UV ink stuff that you can put in your coolant, then test with a mini black light.

 

puddle at the LIM to block join is telling you the story

it accumulates here from one of two common sources

either the coolant barb on top of the rear plate is leaking
( feeds coolant to the BACv and the wax cam on TB,, returning to the rear of the water pump )

or the O ring that seals the crossover port from block to LIM has failed
( turbo engines have the rear housing crossover functional and feeds the turbo cooling water via the LIM )

the former issue requires removal of the UIM to see the issue,, replacement 3/8 heater hose or even EFI fuel hose will fix the issue

the latter requires you to remove the turbo,, UIM and LIM,, all to change the 5 cent O ring that is in the rear housing crossover

 

bumpstart, exactly what I was going to say.

 

Thanks for the help guys. I think it's scenario #2 with the faulty o ring because I just had the UIM off and nothing seemed to be leaking around there. It's a good time to get this fixed because I need to take the turbo off soon anyway to replace my cracked manifold. And an excuse to get my injectors cleaned.

Question about the o ring though. Is it a special mazda ring or is it just a standard size I could pick up at a local parts store? And does that coolant pipe run through the LIM gasket? I have an extra one and I can't really see a spot in the gasket that would be for a coolant passage. They all look like stud holes except for one odd shaped hole that's at one of the ends. I only ask because I've yet to take my LIM off and I want to have an idea of what I'm looking for.