Background:
1. Fresh motor, about 2000 miles into break-in.
2. ARP head studs and Cometic MLS headgasket.
3. Head torqued to 60ft-lbs in 4 increments during assembly. Have not retorqued.
4. Clean, rustfree and straight 216,000 mile 1990 (the silver car) with original heater core and fresh heater hoses.
5. Small coolant lines deleted, reroute from BEGI spacer with a GM truck hose, front water neck blocked off.
6. Newish OEM-replacement auto radiator (plastic/aluminum). Fresh radiator hoses. Fresh 16psi cap.
7. Mitsubishi Turbo, oil cooling only.
8. Running temperatures, monitored on a real temperature gauge, have been good. I did see ~230F while doing extended fuel tuning between 6000-7000 in 95-100F ambient (the OEM gauge moved from 11 O'Clock to 12 O'Clock when this happened). When I backed off it cooled right down. Other than that, always 195-210F.

Here's what's happening: After accelerating (say, from a stop to highway speeds), I get a slight smell of coolant in the cockpit of the car for a few seconds that then goes away. This is with the top down. Usually, it happens when I use some boost (say 7psi or so), but I've also noticed it sometimes at lower boost when I would let the engine wind up a bit. If I drive like a grandma, I don't get the smell. When I pop the hood, there is no smell of coolant anywhere -- it has that nice new-engine smell. I've been monitoring the coolant level for a few days and cannot detect any coolant loss.

Some theories that aren't adding up:
Heater Core: Maybe, but the only symptom is that occasional smell. No fogging windows. No wet carpet. Etc. Also, if it's the heater core, why would it be related to accelerating? Seems like a heater core weep would be related to cooling system pressurization and I should be smelling the coolant all the time after warmup. ??

Head Gasket: In the past when I've had a headgasket problem, the coolant system would pressurize and I would get overflow. The smell of coolant would be strong in the engine compartment. Nothing like that is happening.

So . . . ????

Planning to do a cooling system pressure test and a leakdown test. Maybe something will turn up. But if anyone has any suggestions, I'm all ears because confusion!

 

what if its small enough that only happens at peak pressure?

 

I assume your comment relates to a HG problem. What confuses me is where I smell the coolant, in the cockpit but not in the engine compartment. Would it be possible to suck coolant into the cylinder on the intake stroke but not also pressurize the water jacket on the combustion stroke?

 

No I am talking about the heater core
Head gasket a possibility to but the cooling system does generate a bit of pressure under hard driving and perhaps causing the core to leak

Kind of a longshot though

 

Hmmmmm . . . . So, spinning up the water pump. That's a thought. If that's happening a cooling system pressure test should find it. I could also bypass the heater core and drive around a bit.

 

when my heater core went, I would have coolant smell only when running the heater, and same with fogging windows -- even then, the windows didn't fog hardly at all, and I'm in friggin' oregon.

I vote heater core.

 

Coolant smell inside the car usually indicates the heater core.

Mary's has developed the smallest of leaks.. about three weeks after installing a 16psi cap and a weekend at MMRLS.

 

Somewhat related, but has anyone found a source for 1.8 heater cores? Doesn't look like there's an aftermarket part available and OEM is like $300..

Is the 1.6 close enough to fit?

 

My coolant smell in the car was the heater core. Tom at Parts Group saved the day.

 

In my experience you know when it's a heater core.

I'd just go rent the pressure tester, fastest way to find where the leak is. I doubt it's a head gasket, when I've blown a HG it usually leaks water into the cylinder, spark plugs will show this of course.

 

I did a pressure test this morning and, sure enough, slow leak. Poking around under the dashboard, there is evidence of leakage from the heater core box, but nothing wet/fresh -- so still not 100%. I'm planning to isolate the heater core from the system and do the pressure test again just to confirm.

Which brings us to parts . . . . Poking around on the Mazda Motorsports website, dug up the following numbers and racer costs:

NA6 NA01-61-A10 $271.51
NA8 NA75-61-A10 $253.83
NB Pre 6/2000 (there's a SN cutoff) NC10-61-A10 $279.95
Post NC10-61-A10A $279.95

Couldn't really tell what the interchange possibilities are. Rock Auto lists heater cores for NA6 and NB in the ~$60-80 range, but the NA8 core is shown as out of stock. Looks like I lucked out with a 1990.

If I pull the dash, I'll be able to go all JeffBucc on the inards of my HVAC!! Kind of exciting (not!).

 

or just buy a hyper re-route and run it through the dash

 

I miss props.