Missing coolant
 

Hi all,

So I went and started my car last Thursday and got the dreaded low coolant light and buzzer. I shut it off immediately and checked the dipstick. The dipstick was dry.

I haven't seen any leaks at all, nor have I smelled coolant at all whenever I got home and opened the hood.

I bought a pressure tester and this weekend I refilled the system. Only about 1/3 gallon of coolant/water went back in the system, then I cranked the heater and ran the car for a minute to try to bleed it out. The pressure test showed that the system holds pressure up to 13 psi, then the 0.9 bar cap on the AST lets go and I hear burbling through the AST into the expansion tank. Pressure settles in around 10 psi.

I ran a dynamic test with the engine running. On startup, from cold, pressure does not jump at all. After idling about 5-10 minutes, the system seems to creep up to between 5 to 10 psi. I topped it off after it cooled back down, which just filled the neck back up. Not sure if there is an appropriate bleeding procedure for this. I used one of those funnels that helps you top off/bleed the system for all this, at least.

We went to see a movie on Saturday night so I put about 20 miles on the car, going there and back. It ran fine. The next day I checked the coolant levels and they don't seem to have gone down any significant amount.

Car and original motor has ~15,250 miles, system was flushed and new radiator hoses installed on 11/14/2016 at ~14,050 miles. I have not opened the cooling system since then. Stupidly, I did not think to keep tabs on the coolant level either. I will be checking after each drive from now on!

The car has only had one spirited drive up Palomar Mountain here in San Diego in which it did get plenty hot in the engine bay, but the temp needle did not rise past its center float at all (and frankly, I was stuck behind a Camry most of the way up the mountain so it didn't get pushed very hard).

I am a bit nervous based on things I've read by searching the forum! Any ideas on where my coolant could've gone based on this info? Crumbling coolant seals would be a very sad diagnosis.

Thanks in advance.

Put some cardboard under it and heat cycle it. See if anything is coming out of it. If you have a coolant seal issue, your symptoms will continue and intensify. If not, no problem. I'd fill it up and see if it drops over some weeks/months of use.

If the car doesnt smoke white after hard pull and if you dont see coolant in the oil, most likely your water seals are ok. Maybe you have a small leaking hose somewhere.

Thanks. I haven't seen any smoke. Checking the oil is a good suggestion. I haven't seen anything alarming on the dipstick, but I could always drain the oil pan to be sure.

definitely going to start monitoring the coolant levels! I'll try putting something under the car but I really haven't seen anything at all.

Coolant mixture?
 

What are you running for coolant? If it's not a close to 50-50 mix of green antifreeze and distilled water, you may have boiled some coolant out due to low coolant boiling point after your hot run and not noticed the loss until the next day.

Also, was this the 1st long drive after a coolant replacement? If so, the system may not have been totally bled out before that run.

Disconnecting the small coolant hose on the top LH rear of the intake manifold helps bleeding when refilling coolant.

I can't confirm what they filled it with at the shop when it was flushed, but barring any other direction, I would expect they did 50/50. When I added the 1/3 gallon on Saturday, I used a 1:2 ratio of coolant to distilled water. SoCal weather.

The November service occurred in LA (about 1200 miles ago) so it got 100 miles on it back down to where I am--one would expect that it was bled out by that point, although again, like a moron I haven't checked coolant levels even once up to now. The drive up the mountain happened about 200 miles ago, so there is a good possibility that something happened on that run. Nevertheless, to lose that much coolant seems unusual.

I will keep tabs on it and report back! Well, I need to get the AC serviced before I drive it much. My R12 appears to have leaked out, and I'm a huge pussy. :lol:

Well, since you had not checked the coolant for a long time, it was likely never completely full to start. So I'm guessing that the coolant was quite low (i.e., nothing in the recovery tank) before the hot drive, and just a small amount more was lost during it. So when the car cooled off, the next morning air had been sucked in to the point that the low-coolant sensor was uncovered.

If that's the correct scenario, nothing to worry about. Just continue to monitor the coolant level, and if it stays up, you're good.

My thoughts too. 1/3 of a gallon isn't much. It's way too early to jump to the worst case scenario.

Continue to fill the neck after COMPLETE cool down and make sure the coolant tank is at the proper level..but I think you're fine.

Thank you, gents. Hopefully this is nothing, and I appreciate the reassurances. This forum has me so paranoid with this car. :)

I took it out again on Tuesday night for about 30 miles and the coolant level hasn't decreased on the dipstick. Hoping it continues to be nothing!

Wow! Post some pics

The factory temp gauge is crap. If it does rise past the center point, you engine is toast

If your engine over-heated, it could have caused water seal damage (which sounds like your concern). Continue to keep an eye on the level in the water fill neck (not the overflow reservoir) as well as any leaks, especially around the overflow reservoir (bad water seals will allow combustion gases into the coolant pushing the coolant into the overflow reservoir). If you're lucky, it overheated without damaging the seals.

And get an aftermarket water temp gauge to keep an eye on the actual engine temps

One of these days I'll take some pretty pictures of the car. I've been too lazy about that! But I've attached a few to this post. :)


Yeah, I'm used to that sort of thing with cars of this era. That said though, the needle never rose so I'm hoping it didn't overheat.

It's not so much my concern as it is that it seems all of these sorts of stories on the forum have lead to people diagnosing it as a rebuild. :lol:

So just like a blown head gasket, really. Based on that scenario, wouldn't I expect to see the coolant reservoir level go up? If the water neck continues to need filling, that would imply to me that the coolant is either entering the combustion chamber (seems like it should go the other way, with being a boosted engine and all), but that the coolant overflow tank should be getting filled up...?

ANYHOW all speculation right now I suppose. I'll have to check the water level in the neck as you stated, thanks.

I suppose I should get a PowerFC, eh? Not planning on adding gauge pods.

Wow! That things a time capsule

There is cause for concern. Rotary engines and their water seals are not very heat tolerant.

This is a pretty good thread on the subject...

https://www.rx7club.com/3rd-generati...thread-571088/

Yes. The coolant reservoir will overflow with a blown water seal when the combustion gases get into the coolant. There's also the reverse, water getting into the combustion chamber. Symptoms of that are lowered coolant levels and white smoke.

Yes, you could go the PFC route which has added benefit of allowing you to set your fan controls, but I wouldn't buy one to use simply as a temp gauge. If you just want a temp gauge, but hate gauge pods, an RE-A/Pettit column pod is fairly unobtrusive.

And a couple other things to consider to improve cooling if you plan to drive it, are getting a larger aluminum radiator and replacing the pre-cat with a wrapped or coated downpipe.

Yep--when I got it last year, it still had the original tires on it, even.

And so that's the thing, I haven't seen any smoke in the exhaust and the coolant reservoir was dry, not overflowed. So I'm confused and concerned, but will just see how it plays out I suppose!


What are your thoughts on linearizing the temp gauge, as opposed to getting a separate gauge? I don't hear that option talked about much here. But really, I prefer getting an alarm as opposed to having a gauge to monitor, so being able to set up the PFC to flash at me or whatever once the temps start climbing would probably be a better option for me. I'd also get it to smooth out the boost curve and the other benefits that come with it.

Reliability-wise, I have an HKS DP that I've had coated and am prepping to put in, but I want to sort out a few other small details first (throttle tip-in weirdness, possible ground wire/TPS issues). I plan on buying a Koyo n-flow radiator sometime soon to put in as well. Beyond that, someday I'll stick a Racing Beat exhaust on and that's all I have planned. Trying to keep it in a collectible state and drive it less than 2000 miles a year, and also resisting the urge to do all the work at once. Take my time, keep it as a project.

+1 to monitoring temps as Tom as said. The gauge is not linear. There are small (52mm) gauges that even have font and backlighting that comes really close to the dash. Spending $1200 for a PFC just to monitor temps doesn't seem like something I'd do with THAT car. And linearizing the stock gauge seems pretty invasive, assuming you want to keep it as original as possible. A little aftermarket gauge with an alarm in a single gauge pod seems easier to reverse.

Fantastic looking car indeed. Makes me want to get off my ass and repaint mine.
Montego Blue Mica is an awesome color.
Your car looks like it was just driven off the showroom floor, man. :nod:

Maybe all the air did not get bled out of the system back in November. It has not been that hot in San Diego this summer to really test the system. My experience is it takes a couple of drives followed by air bleeding to completely remove all the air after a complete drain and fill. Come to the monthly San Diego RX-7 club meeting and you can go over all the possible causes with your fellow rotor heads and they can give you their favorite procedures for bleeding the system. Unfortunately, you missed last Sunday's six hour club run through the mountains. That would have been an excellent time to wring out the cooling system.

Also, to be useful your temperature gauge needs to be linearized!!! Otherwise it won't move until the car is nearly overheating. Here is my write up on how to do this. Again if you need help with this mod the local club is the place to start.

Ok this is me proselytizing. The stock gauge sensor is in a very unique location designed to give you the earliest warning that the car starting to overheat. This is at the end of the coolant passage that passes between the leading and trailing spark pugs of both rotors. It is the most critical coolant passage and the hottest running passage in the engine. (In the picture the sensor is that little nub just below the oil pressure sensor which is below the oil filter pedestal.)
.

https://cimg6.ibsrv.net/gimg/www.rx7...5b4d7e214a.jpg


Most folks place their aftermarket gauge sensor near the filler neck, this gives you the average coolant temperature of all the coolant in the engine, which is great for determining the overall temperature of the engine and is why Mazda engineers placed the ECU temperature sensor there. It will not tell you that there is a problem in the combustion chambers until that critical coolant passage is hot enough long enough to heat all the coolant up to a high temperature. Bottom line is, if you want the earliest warning that the combustion chambers are running too hot linearize your stock gauge or place your aftermarket gauge sensor where Mazda's engineers determined was the best location.

Agree. I thought of doing that but the problem is finding a sensor that will fit the stock location (think it is BPT but not sure). Or you could tap it

Problem with linearizing the stock gauge is it's a pain and you risk cracking your gauge hood to get to it.

And here's my proselytizing...
You're assuming I'd suggest the WP housing for the sensor. I never did that and, in most situations, recommend otherwise. The OP has a VERY stock, low-mileage car that presumably he wants to keep that way. So use the throttle-body coolant line for the sensor. It sources temperature from essentially the same place as the stock sensor (see your diagram), provides meaningful and accurate readings immediately without relying on the t-stat to open. And perhaps most important to the OP, it's completely reversible...no cutting the hose, just add in a short section with a 'T' fitting for the sensor and you're done.

I have mine where Sgtblue said and i am co fident that it works. Tjere is so much reading in the forum about it.

Did not see it mentioned but do pressure test both the radiator and ast cap. One can rent a tester or bring them to a part store. Have known a few that had problems and that solved the missing coolant problem. The factory cap are a bt pricey but worth it unless you are buying a known brand as a substitute. Also check the rubber seal around the caps and perhaps clean it. Also look at your water pump weep hole for signs of leakage in case the pump is going, this is hard to do but looking for any moisture does not work I found as it seems that any will evaporate before you see puddling under the car. If you don't have hot start problems, i.e. car does not fire up quickly when hot due to coolant being where it shouldn't, that is a good sign also.

Thanks, the paint is about a 9/10 in person, but it passes a three-foot test with ease!

I signed up on the Meetup group months ago and just have not been able to make it out to any of the meets! I was going to try for the drive, but then my AC went kaput and I was worried about all this coolant issue so I decided not to go.


Yeah, I've been interested in this mod for quite some time, although as Sgtblue and others mentioned, it does look like a bit of a pain. I do have to take the gauge cluster out to replace the A/C panel with a non-flaking piece--this is the one interior panel on this car that is in moderately-poor shape, so it may be an opportune moment to work on the gauge.

Sgtblue is correct in that I'm trying to keep this thing as pristine as possible with the mods. Would love to figure out how to set up some sort of alarm when temps start rising though. If one were linearizing the temp gauge, I'd assume I could just run a separate signal line to some sort of triggered alarm setup...

I did pressure test the caps--like I said in the first post, the AST cap held to 13 psi. The fill neck cap doesn't seem to actually vent pressure though, right? I was testing it and it went past 25 psi, then I realized that there isn't any kind of venting mechanism built into this cap, nor would there be an air bleed line up there at the fill neck anyhow.

Car doesn't have any hot start problems either, so thanks for that suggestion. Rubber on this car seems to be mostly in good shape, on the caps too, but the radiator hoses were replaced because the 24-year-old hoses were weeping a bit. No surprise!

That's one of the best things, by the way, about buying an FD with only 13,000 miles on it--all the plastics are still in great shape under the hood, still white and everything. The rubber caps over the relays and other components aren't cracking, everything's still rubbery. Wiring isn't all fried, solenoids are clean, etc. I was being lazy and didn't want to do the vacuum hoses myself, and the shop said to me that they actually didn't need replacement yet--they were all nice and supple, but of course we did it anyways. Sad though because I'd love to put down 350 HP on twins, but... this one's too clean to mess with!

Agree you should keep it as stock as possible, but it is your car. A PFC running 12 psi and light modding (exhaust, hi-flow cat, cheap bastard intake, and a stockish aftermarket SMIC) will get you close to 300 rwhp. Anything over that and you'll be staining the stock turbos, and you'll need a bigger IC, and meth, etc. etc.

And while you have low miles, you don't have low age. You may want to consider a boost gauge to keep tabs on your boost control system (under or over boosting). If you don't like gauge pods, there's a lot of hi tech electronic options out there. PLX comes to mind (MultiGauge Link for Smartphone Interface with PLX Devices Sensor Modules) but I am sure there are others

Yeah the 350 hp thing would've been with me switching to '99 spec or BNR twins with a street-ported engine of some sort. That was the goal before getting this one.

But you've said it best--this car has low miles but not low age. What happens to a car when it barely gets driven in 24 years, right? I have already encountered a few little glitchy things to fix (like right now, throttle tip-in is herky-jerky. ISC seems to work fine, dashpot is fine, I'm thinking I need to test the TPS next. High idle is a little weird too) and am on the lookout for more.

I don't intend to up the boost, and the only reason I considered the PFC was to control the boost spike once I put in the downpipe and cat-back, but maybe also get some moderate gains with a tweaked base map I suppose. Really don't want to have to rebuild the turbos or the engine though, and once you blow one thing up it's always tempting to increase power. "just one....more...thinnnnng!"

I haven't been in the modding game in about ten years. I didn't even think that someone might've come up with a smartphone gauge solution. That could be interesting--thank you for the link! I could easily see buying an iPod Touch to keep in the car and put on one of those magnetic vent mounts to use as a boost gauge instead of a gauge pod, especially in a situation like mine where I'm trying to keep the car fairly stock. I did already swap out the double-DIN stereo for a single DIN (with the R1 single-DIN pocket below it) just because the LCD backlight was dead on my radio, but I have all the pieces still.