Missing coolant...

I'm taking the Miata rallycrossing tomorrow so I spent last night double-checking nuts and bolts, regreasing the brake caliper pins and topping off fluids. Well, it appears I'm losing coolant... The resevoir was just about empty and I topped it off about a month ago when I did the timing belt.

Being that it's a 16-year-old car and the lack of any evidence of it burning coolant - I think I have a leak. The hoses are all original, and I did spring a leak from the upper heater hose this summer at the track (cut the end off, stuck it back on and continued). I'm not seeing any puddles in the garage, but it doesn't spend any time running there, and the leak is likely only occuring when the system is under pressure.

So I guess my question is: Where can I get a replacement set of coolant hoses for the cheapest? Rosenthal wants $100, but I don't know whether that's cheap or not.

If it's not on the floor, chances are it's going out the tailpipe, either pre or post combustion. Time for a proper leakdown test.

In reply to DaveEstey:

Is that for the whole set? Radiator and heater? That seems to be a good price.

I've ordered a reasonable number of parts from Rosentahl and I'm generally very happy with the price.

That's whole set.

The exhaust has never smelled sweet nor have I seen evidence of any white smoke so I don't see it going out the pipe. I also have a slight exhaust leak right off the header so the smell would be pretty evident.

Does it still have a heater? If so, heater core is leaking out the evaporator drain hole, especially if you haven't used the heater in ages.

Could be a pinhole somewhere. Take it on a backroad, run it hard 0-90 then pull over, pop the hood, and look for the spray. Also pop the plugs out and see if one is whiter, that's a head gasket. Worst case, I have had good luck with the standard bars leak brown sludge in a bottle stuff for slow leaks.

Ranger50 wrote: Does it still have a heater? If so, heater core is leaking out the evaporator drain hole, especially if you haven't used the heater in ages.

It's my daily driver so I'm using the heat just about every day.

I'm going to run a leakdown test on it next weekend - need to borrow the tester since I don't have one of my own. I'll check the plugs tonight.

The last leak was a pinhole that only showed when running - soon as you shut down the leak stopped - so I'm expecting this is the same. I had the typical CAS o-ring oil leak and didn't replace the hoses at the same time so I've basically been on borrowed time.

Before I had to do the head job on my Nissan truck, I was losing a lttle coolant and oil. I could not find any leaks. I could smell collant down in one location beside the engine, but never found a leak. Later the engine puked on me and I knew I had blown a head gasket. Removing the head showed a definite leak between 3 and 4. I could not see it or smell it coming out of the tail pipe either.

I'm definitely not losing oil and my most recent change looked nice and clean so if I'm losing coolant it's staying out of the lubrication system at least.

If you're doing a wholesale swap on the coolant hoses, make sure you get the 3 little ones go from the water neck to the throttle body, then to the factory oil warmer (on the oil filter mount) and then to the back of the head. A few years back I somehow wound up with something in my coolant system that rotted all of the rubber hoses. I swapped all but those 3, and then had one of them fail on me at Laguna, which kinda sucked. AAA plus was used to get home, and while I never had conclusive evidence of damage resulting from the incident, I'm sure it contributed to the ring-related leakdown that lead to a motor rebuild a year later.

I would buy the replacement parts from Mazda Motorsports/Mazdacomp. I dunno if rallycross is part of their system or not, but if so then it's well worth signing up IMHO.

I already have a Mazda Motorsports account for my RX7, but I don't feel like going through the trouble to get another for the Miata.

Yes, they make you have two separate accounts.

This is the coolant hose kit in question: http://parts.arlingtonmazda.com/products/COOLANT-HOSE-KIT-%28PKMIAD1005%29.html

Did aanyone mention pressure checking the coolant system.?

I'm doing that next weekend as well. Thank god for making friends with shop owners.

Pulled the plugs Friday night and they all look great (whew). Ran the car hard at rallycross on Satuday, hosed it off Sunday and found a small pool of coolant under the car today, so I'm guessing the leak has gotten a little bigger and is finally revealing itself.

that's a good way to find a leak. It was probably a pinhole like you said that only leaked when not.. and it was probably being boiled off as it was landing on something hot

Sounds like yours is obvious now, but I had an overflow cap on my E36 that would spray a fine mist of coolant when the car was running, but would never leave any drops under the car. I think the gasket on the cap was shot, so I got a new one. Problem solved!