Coolant leak -- from where?
 

My MSM is loosing coolant at an alarming rate.

I haven't found any puddles, so today I brought the engine to operating temp, waited until the fans went on, and gave it throttle with a big piece of cardboard under the engine bay (the undertray is long gone) ... sure enough, there were significant coolant drips on the cardboard, coming from the middle/back of the passenger side.

What should I check next? I'm not familiar with where the coolant is routed through the engine. Are any specific parts in that side/corner of the engine prone to leakage?

(Had the head gasket done by a Miata specialist last summer, so I'm not terribly worried about an internal leak.)

I recently had to replace my water pump due to it leaking. There is a weep hole on the front/radiator side where coolant will escape when the seals are going bad. This drips down around and inside the timing belt covers, and can sometimes make finding the source a bit difficult. I was at 54K after I'd done the last timing belt service, so I bit the bullet and re-did the timing belt service a little early as you have to get all those pieces out of the way to do the water pump anyhow.

You have a water-cooled oil cooler.

Buy a complete hose kit from Rosenthal or some other OEM outfit and get things up to snuff. While you're at it, get a replacement undertray.

Instead of holding up a piece of cardboard, you should actually trace the leak to the source. Get all up in there with a flashlight and whatnot and you should see it. My green miata was purchased with a freshly re-done head. Brand new hg and everything. well it actually leaked coolant at the hg on the passenger/rear of the engine. Removed head, replaced gasket, cleaned everything up and re-installed with proper torque and torquing procedure. Good as new.

Before you get into tearing off the head though, you need to actually find the leak. If you can't put some dye in the cooling system and do the black light method. 100% will find the actual spot its leaking from.

That task is WAAAY over my head (pun intended).

Google search indicates that green 50/50 is already UV-sensitive. Whilst I wondered where to buy a decent blacklight, my girlfriend suggested the pet store -- said she bought one there many years ago to find where her cat peed (!!!) on the carpet. Apparently cat pee is * also * UV-sensitive.

I'll give the blacklight method a try later this week. Supposed to rain from tonight until Friday morning.

I'm with hornetball. I'd suspect something around the oil cooler. There's a small water line coming off the throttle body that goes to just above the oil filter, then leaves the oil filter and goes to the back of the block. You should be able to jack the car up and look under the alternator and see if one of those lines are cracked.

You have a few more hoses than this diagram and there are some to turbo, but I believe all the passenger side items are the same. Start checking hoses.

https://www.miataturbo.net/attachmen...ine=1360602321

Most likely the small hoses going to the oil cooler.

Is the oil cooler the part circled in green?

https://www.miataturbo.net/attachmen...ine=1369333361

No, thats a 1.6 motor diagram.

Ah I found a diagram in the MSM service manual:

http://www.snarc.net/cooler.png

Along with a drawing showing the in/out prongs. That should help me find it.

That little "L" shaped piece between the oil cooler and oil filter is where the coolant line connects.

Thanks .... I'm not that clueless, but you meant well. :rofl:

Great news: mechanic says my car only needs a $17 hose. :winner:

I was afraid I'd have to sell a kidney to finance major engine surgery.

Mildly annoying news: he won't have the part until Tuesday.

So! Everyone got it correct. The bum hose was the one from the back of the head into the oil cooler. Mechanic replaced the hose from the oil cooler to the throttle body while he was at it.