rx7tt95

A bit of background, I've installed a 13B-RE Cosmo 2 rotor into my FD. The engine was taken apart, ported, and rebuilt with new internal parts. After about 3K miles, the engine started burning coolant but the caveat is that it only happens with boost above .75kg (about 9psi). I've been upping the boost slowly and tuning via datalogit/wideband as I go and as I went from .75 to .85, the engine began to burn coolant. I use an AVC-R and I did have a boost spike of .94kg while the controller was learning the boost curve. Naturally, all fuel settings above my target boost level are very rich for safety.

Here's where it gets interesting. After "swallowing" a bit of coolant, I can drive the car as normal (it'll die if I try to idle it) and eventually, it clears out and runs normally at low and off boost (vacuum).

After noticing a "pit" in my front primary port runner, the shop which built the engine determined that was the offending cause of the vacuum leak. I accepted that and searched around for a Cosmo center plate to no avail. I called Pineapple racing and they recommended a particular brand of epoxy which I promptly ordered with overnight delivery.

I've been cleaning the offending part with acetone and for the life of me, I can't see how this thing is causing a coolant leak. There's no visible hole, light doesn't shine through it, and acetone pooled around the spot in question does not leak through.

So the facts are:
1) car burns coolant but only seems to do so under boost conditions above .75kg/cm2
2) car does not seem to burn coolant under .7kg/cm2 or under vacuum conditions
3) coolant residue was found in the uderside of the oil filler cap
4) if I boost above .75kg/cm2 and the engine "swallows" a bit of coolant, I can rev it, drive around a bit and the coolant will clean out and the car operates normally. 100% normal under vacuum conditions. Vacuum levels are just fine, about 375mm to 410mm at 1100 rpm
4) there seems to be a pitted spot in the front rotor's primary intake runner
5) we can press on it with force and it does not open up or give way

After I cleaned it, I had the idea of sealing off the ports. They did this at the shop too, using hands to block off the ports and using compressed air. A thin sheet of paper, stuck in the coolant passage below the port fluttered when air was applied to the port.

I decided to duplicate that experiment but I used thin latex gloves and towels to seal the ports. The soft latex provided a good seal. I also plugged the small port inside the injector bung and proceeded to blow as hard as I could (no jokes please) into the top of the injector port. Enough force was applied that eventually the glove/towel combo was pushed out. No air seemed to leak into the coolant passage.

Since it only leaks when boost is applied, I would think that the coolant would leak under vacuum conditions as well as under boost. The coolant system is under far greater pressure, 16psi to be exact, so theory holds it would leak all the time, no?

I'm about ready to run back over to Walmart and purchase a bit of playdough to really seal everything off but I'm almost ready to bet my left nut the "pit" in question is not causing the leak. I'm footing the bill for the whole fiasco since the shop has determined that my port job was responsible for the coolant leak. I'm now wondering if it's a convenient scapegoat for not assembling/checking the engine properly.

Where are common areas that leak coolant? Besides problems with porting, afik, they can leak around the spark plug area. We tested that. Nothing. Now, if the plates weren't checked for flatness and there was one small area which was uneven, higher boost levels would expose this weakness wouldn't it? If the bolts weren't tensioned properly, unevenly or too tight, problems could be created, correct?

Thing is, if the engine were expanding laterally, it seems like oil/coolant would leak OUTSIDE the motor as well, not just inside. Or at least that's what makes sense to me.

Here's the offending pit inside the primary runner. This photo is taken looking down the primary injector port. Notice the "plug", round shaped piece of metal of different grade in the bottom of the port. Both sides have this. The pitted area is on the outside of this plug. You can see the scrapes from trying to press through with a screwdriver (had a right angle head).

rx7tt95

Here's a second pic of the rear primary runner, same plug/disk shaped thing on the bottom.

black_sunshine

It could be a bad turbo. Check the bushings/bearings and make sure there's no play on them, especially the water-cooled parts.

But since it only happens ON boost above 8psi, that's interesting. At first I thought it might be on the intake side of the motor, but then it'd do it all the time. Then I thought it'd be on the combustion side, but that'd just exhaust into the coolant passages.

It is possable that the outter water jacket seal is leaking towards the bottom, leaking into the oil pan, and getting into the combustion housings via the turbo (when it spools faster, it may have just enough slack in the bushings/bearings to leak some water in...). Hmm....

Other than that this is a good problem )

If you REALLY don't want to rip into your motor and try to fix it, I REALLY hate to say it but try some stop-leak. Do this as a last-resort though. Exact process (it really does work) is at http://www.rotaryresurrection.com/coolantfix.html

Make certain that the stop-leak doesn't plug the turbo up though; if that happens, bye-bye boost.

I'm really uncertain about it being a coolant seal leak. If it were, it'd do it ALL THE TIME; I would think that if it were intake-side related (leaking runners or otherwise), that under boost the problem would go away due to the equalization of pressures (coolant pressure VS Boost pressure); or you'd have overheating problems. Bingo! Do a coolant-pressure check. Pump it up to ~30psi and leave it for a few days. Maybe that'll help pinpoint the problem. Stant and others make good pressure-checking systems (O'Reilly's or Auto Zone) for around $50 or less.

Other than that, I'm out of ideas.

That area on the intake runner is where they held the casting; it originally had a dowel through it and after the initial casting, they re-cast some metal into that before porting. Shouldn't leak, but that doesn't mean it isn't.

hope this jumble of thoughts was some help to you

Matt

black_sunshine

Oh, just thought of something else; you could have a hairline crack somewhere in the intake and under boost it just enough to open it and let some water in. Unlikely, but it's a possability (9lbs it barely enough to stretch a rubber hose, none-the-less an iron casting).

rx7tt95

Thanks for the input Matt :-)

We finally figured it out after going through a miriad of ideas...everything from porting too far to warped housings to microscopic cracks that are opening up only when the engine is hot.

Essentially the shop assembled the engine minus the rotor/shaft and pressurized the cooling system. Hearing a hiss at 20psi, they then filled the block with a bit of water and began poking the intake runners a bit. Water came out the rear secondary port. Strangely, when I showed up to check it out, it wasn't leaking at 20psi. They pressed on it and out came the water. So...when the car was under vacuum, it wouldnt' leak. Boost would push it "up" ever so slightly and it would spurt coolant. Very frustrating. Instead of hunting down a new plate, I'm using a special epoxy recommended to me by Pineapple Racing. I should be good to go by the weekend (fingers crossed).

rx7tt95

LOL, think we replied at the same time...you hit the nail on the head!