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Probable blown coolant seal - what to do to minimize damage?
I'm pretty sure I have coolant leaking into the trochoid chamber(s) on my 91 NA RX-7 - original motor with 170,000 kms (a little over 100,000 miles), and regularly autocrossed for 21 years, with a lot of highway kms in between events since most events have required an hour and a half drive to get to.
I'm looking for advice on how to minimize corrosion and other internal engine damage in the short term - I don't have time to pull the engine right now, and in a couple of days, I'm leaving town for a few days to visit my family in the next province over. My thought is to drain the coolant as completely as possible, then run the motor for a minute or so, just to clear any remaining liquid from the chambers. Does this make sense? I don't think it will get hot enough in a minute or so of running to warp or damage the housings, seal springs, etc - will it?
I'm minimally employed right now, so while it would be nice to think of this as an opportunity to rebuild for NA "power", or do that S5 turbo/LS/V6 swap I've long dreamed of, etc, the fact is I probably will have to just try to do a basic rebuild to save this engine and keep the car, hence my concern for preventing additional damage from it sitting with coolant in the chambers for a couple weeks or so, until I can pull the engine.
Background:
The car was very reluctant to start a few days ago, when I last drove it before yesterday (it had sat a few days after an autocross the previous weekend). I thought it had somehow flooded; maybe a leaking injector - it ran very rough, like it was on one rotor, and a lot of gassy smoke, but once I was able to coax the revs above 1500 or so, it stabilized and ran smooth, seemed to drive normally - hence why I thought flooding. Same thing happened again yesterday morning - very rough and hard start, lots of smoke, but once running, it ran fine all day - 7 hard runs autocrossing, and about 320 kms of highway drive there and back. But when I stopped near home to wash the car, it was again hard to start, despite sitting only a few minutes. Again, at home after, I shut it down a few minutes to swap my daily out of the garage, really hard to start. While looking under the hood, I noticed the coolant bottle was significantly higher than normal - and then it dawned on me - blown coolant seal. While running, there seemed to be a steady stream of bubbles from the tube in the recovery bottle, and when I had my wife start the car, I was distinctly able to smell the coolant in the exhaust, as well as see the steam, despite the car still being warm, and it being 26C out. So, pretty clear it's leaking coolant internally. Fortunately, the oil looks clean.
I appreciate any tips and advice. There is a local rotary shop, RX7 Specialties/Rotary Engine Specialists, and I'd frankly love to just have them rebuild it - I've read/watched a lot of project builds over the years, but never been inside a rotary myself. I doubt I can afford that, but it does mean I can potentially source some of the seals and stuff locally.
Thanks in advance,
original motor with 170,000 kms (a little over 100,000 miles), and regularly autocrossed for 21 years, with a lot of highway kms in between events since most events have required an hour and a half drive to get to.
You got your monies worth
It may be more economical to get a new shortblock vs rebuilding what you have. To truly determine, you'll need to tear it down to evaluate the irons and housings
And i don't think sitting a couple of weeks will matter all that much. If you are expecting any long term lay up, i'd tear it down, bag it and tag it.
I ended up draining the coolant after a short drive to warm it up a bit (to promote drying the chambers once the coolant was out), let it sit a while to cool with the rad cap off to avoid pressure pushing coolant into the chambers, drained the coolant from the block and rad, and once it cooled a bit more, ran it thirty seconds or so, just to make sure no coolant is in the rotor housings. It fired right up and seemed to run completely normally that time. The leak is on the rear rotor; the lead plug there had some ashy-looking deposits on it, and a peek with my boroscope showed the rear rotor had noticeably less carbon on it... presumably from steam cleaning! So I’m assuming all will be well until I can get at it in earnest.
After you have drained the engine and ran it a short amount of time to burn out and residual coolant now would be a good time to use fogging oil to coat the internals to help prevent corrosion.
i have a 1986 GXL and i bought the car almost 2 years ago now and i bought the car with a blown coolant seal without knowing or so i thought it was a blown coolant seal. I was devastated when i drove the car after i bought it and it overheated on me after just driving it around the neighborhood teaching myself how to drive stick better. Eventually i learned how to combat this problem I've been having by just filling the engine with coolant once and a while but i wouldn't top it off because when i would park the car and turn it off the overflow tank would be full and sometimes spitting coolant out at an alarming rate. This is because the combustion gasses from the combustion chamber were getting into the coolant system evaluating my theory of the coolant seal being blown. It was strange though i did a block test and it checked out and seemed fine. I ended up daily driving the car far almost a year and got very good about my trick and towards the end of summer when i would have to start commuting to school it got worse and i was having that rough startup exactly like you were describing where it would not want to run and after it would do a "puff puff" the engine would run without an issue but after it did that for 2 weeks it kept fouling my spark plugs i ended up getting new plugs and within 2 days the same thing would occur so that is when i knew i needed to rebuild my engine. Upon pulling the engine apart i have discovered that my coolant seal theory was untrue and that the center iron failed. The wall between the coolant passage and the coolant seal grove had broken off on both sides of the center iron indicating that both rotors were getting coolant in the combustion chamber when the engine was off and pushing gasses through the system when the engine was running. I have spoken to Adam over email from Rotary Specialists about my engine and my center iron is garbage. The housings are beat up and are on the edges of the housing where they meet the center iron are becoming unchromed but i was assured that the housings could be resurfaced and could be run again they just wouldn't have perfect compression. Other then that the rest of the engine looks great the engine only had 73k miles on it. This could be a very similar situation to what your engine is experiencing. I hope you have a lot better luck with your engine then i do with mine but i left a few pictures of my housings and center iron to help you understand what could have happened.
Chris - I'm really hoping the irons and housings are good, but it has occurred to me that the problem could be the groove for the seals too; I'm hoping not, the coolant is in good shape, still pretty bright green, so I'm hoping it was doing its job and preventing corrosion, but I won't know until I get the motor pulled and disassembled. That might not be soon, money is tight and as much I miss my summer toy already, it's not a life priority.
07-27-20, 09:29 AM
