This is not good, right? Maybe combustion gases escaping through coolant seals into cooling system? 112K+ miles on original engine, just happened today for the first time after a 30-minute drive in 85°F temperature. Temp gauge looked normal, but from engine shutdown to about 10 minutes later, heard boiling coolant, and the coolant dipstick was wet way above the "full" line. Am waiting for it to cool down now. FC coolant sensor is installed, fan mood is deleted. Maybe the pressure seal in cap is out of spec? Should be what, about 13 psig to open? [Edit: After a 2-hour cool-down engine is still pretty warm, and level in the coolant reservoir is quite low, maybe 20% left. I refilled it and will have another look tomorrow.]

Any advice welcome, thanks!

 

Coolant above the full line while the engine is still hot is normal. With a sealed system it would be drawn back in as everything cools down. And yes, you should have a .9 bar/13 psi cap.
Do you have an aftermarket temp gauge? Sounds like you have air in the system, hence the boiling sound. It could be something as simple as a bad cap, it won't cost a lot to replace them. Burp the system, refill and see what you get. But given your mileage...well, you know.

 

Yeah, I know. The boiling in the reservoir was major, and the upper fill cap was actually letting a little coolant out. Maybe it is just a cap problem... I'll check for parts with our Mazda dealer. This morning, under the upper cap area I couldn't see coolant, but the reservoir had not dropped level since I added coolant, i.e. still very high. So I added coolant to the top cap area... took quite a bit, maybe a quart. I try to keep all the fluids topped up, so this was a surprise. No coolant leakage onto the garage floor, can't see anything wet in the engine compartment. Since there was a little coolant bubbling out the top cap, maybe it was also letting air in as the engine cooled.

Thanks for your response! (Oh, temp gauge is OEM.)

 

+1 for burping the system. I had the same problem when I first purchased my FD and that solved my problem. I ended up purchasing a new OEM rad cap because the gasket was worn.

 

Just had the car CA smog tested - it passed. But the car dumped coolant on the tech's floor. Drove over to the Mazda dealer and ordered the two rad caps; will pick up tomorrow. Hope that's all it is!

 

The easiest test you could do is wait for the car to cool off, remove the upper coolant cap, and start the car. If it's bad coolant seal you will see lots of bubbles coming up. It will happen pretty quickly too, don't need to fully warm up.

If you don't get the bubbles, then coolant cap, a hose or something cheaper than an engine is likely your problem.

 

i see that your original motor is at 112k... my guess it rebuild time lol...

 

I am in the 'rebuild time' club, too...


Sorry.

 

Sorry to hear that Gregg, been there. Don't wait too long. Maybe time for simplification and a PFC?

 

Exactly, thanks. I was putting off the champagne test until after I had the new radiator caps. But you are right, and I will do that test.

 

lol!


No, I meant to say I think he is going to need a rebuild!


Mine is still going strong, thank God...only about 10,000 miles on the new engine.


I'm just thinking, based on my experience (and countless others here), that it's wishful thinking to assume anything else.

 

^ Ah...good.

 

I'm trying not to assume either way... still investigating. BTW, I noted that the yellow warning labels on the two new rad caps that I installed yesterday are not completely the same as the OEM ones I removed. On the old ones, both the upper and lower cap labels read exactly the same, i.e. "Never open when hot." The new upper cap label is exactly the same, but the lower cap label reads "Never open," and has a picture of a hand with a line through it. Does this mean leave it closed hot or cold? It reads the same in both English and French. Why would they change the AST cap label?

 

The filler neck is technically a higher point in the system than the AST. Though I've never had an issue opening either, maybe it's to avoid spilling coolant by opening the lower point in the system.

Matt

 

I agree, it's too early to know for sure. This might help you understand better (if you don't already) and it has all of the symptoms I could think of that are associated with a coolant seal failure. https://www.rx7club.com/3rd-generati...ystem-1068344/
And note that at least IMO no ONE symptom (i.e. air in the system) is confirmation.

 

Very good thread; thanks, Sgtblue. Will be doing the champagne test later today. Are there any reliable rotary engine rebuilders in the Orange County, CA area?

 

I believe DNA


But you have
Lucky 7
R&R
Garage life

 

@Rotary Yo,

Thanks, but I don't understand.
1. What is "DNA" other than de-oxy ribonucleic acid?
2. What are "Lucky 7," "R&R," and "Garage Life?" Should those be links?

 

I thought you were looking for a rotary shop

 

 

Indeed. Preferably English-speaking.

 

I purchased my Rx7 from Garage life in SoCal. It was in very good shape when I purchased it bone stock. I was pleasantly surprised to pull the UIM and see that they had replaced a few solenoids and the turbo coolant lines were a hefty strong aftermarket variety. I've heard lots of great reviews about them.

Matt

 

I bought my first 3rd gen brand new May of 92. It's always gurgled on shut down. At first I thought I wasn't letting it cool down long enough but it didn't matter how long I let it idle it would still gurgle. And still does to this day. It was a daily driver for the first 28000 miles , it has about 42000 on it now, mostly autocross and track days after the 1st 28000. Not losing any coolant not running hot, I don't worry about it anymore. Got my second one for racing a month or so ago it has a single turbo conversion and it does the same thing.

 

Still haven't run the champagne test yet... "gurgling" never bothered me, but "full boiling" in the reservoir does. We'll see how it does with the new rad caps.

Wow, May '92? Really?

 

Yup😂 I'm an old fart... not to say you don't have a serious issue, just hoping it's the same thing mine does and you may not have to do a rebuild yet.