Head Gasket or?

I think I may have a HG leak. It isn't very large yet since I don't see it in my tailpipe. I just recently changed the oil, and did not see anything special. However, I do seem to smell a trace of anti-freeze in the air at startup, and when I come to a stop. This is on a boosted 1.8L miata. (since 97)

I slowly loose coolant over time. I've recently replaced the radiator cap and thermostat and never had it grossly overheat. (I replaced both because of minor overheating. No more overheating.) No puddles or other evidence of a leak. The coolant loss is slow compared to a daily check. However, over a week or two, I need to add coolant (well, water right now, since I don't feel like wasting it...) to top it off. The coolant overflow container becomes bone dry. Yes, I do fill the rad and the coolant overflow to the right levels.

Is the definitive method a leak down test? Can I just get http://www.harborfreight.com/cylinder-leak-down-tester-94190.html for the test?

One more question - assuming it is the HG, do you recommend new head studs? New intake and exhaust gaskets?

Thanks, Bruce

Sounds like HG leak, I had same symptoms on a Northstar in a Cadillac, tell me does it run kinda rough at startup till it warms up?

Two tests you should do, go get a $50 block tester die kit from NAPA, it's fast and easy, not always 100% accurate, then yes, grab a leak down tester (higher pressure preferable, the 10psi kits for $35 from Harbor Freight aren't that good) and do a proper test.

Goodluck...

Better to do all gaskets while you're in there and have it all apart anyway, exhaust, intake, valve cover, all of it. Studs require periodic retorque, however are pretty much good for the life of the engine and can be reused, mostly personal preference.

As a professional, I can tell you that confirming a head gasket failure, before it becomes badly obvious, is real hard. The hydrocarbon tests are iffy, and a small leak won't show up with 150 psi leakdown- it probably only leaks at much higher pressures.

If you absolutly can't find the source of the loss, and can smell it at the tailpipe thats getting pretty close. If it starts to miss for a few seconds on cold start, thats pretty much a guarantee.

Next time I have one I'm not sure about, I'm going to pull the front O2 sensor and see if its green. Apparently the antifreeze will stain the sensor. And ruin it too, but thats an extra.

It's not out of the question for the head to be lifting under boost just a tad.

Raze & Streetwiseguy -

I hadn't really noticed the miss at cold start. When one has an aftermarket ECU sometimes it is hard to tell if it is the ECU or a real miss. I'll check it out tomorrow morning.

Ack! that would be tragic if it hoses the O2 sensor. I've got a wideband in there, one of the old expensive bosch units. I wasn't planning on replacement of that. My WB is just ahead of the cat - would anti-freeze staining be present 3-4 feet from the engine?

No issues on cold start. Can't smell coolant in exhaust stream. Waited a while for engine to warm up, still no coolant smell in exhaust.

However, I did find an oil leak at the CAS (crank angle sensor) at the back of the valve cover. It seems that some hot oil is dripping on the coolant hose exiting the back of the head. I've had this problem before - hot oil on a coolant hose = some leaking or weeping coolant. While the engine is running there is nothing obvious going on, but there is clearly some oil on the underside of the coolant hose.

I'll replace the hose first. Hopefully that will be the problem. I do have a spare CAS O ring and VC gasket, so maybe this will be a cheap fix. IIRC, that hose clamp is really hard to get to...