fd3stiny

iTrader: (4)

I'm having a WORLD of overheating/boiling problems that never existed before i "corrected" my closed cooling system by going back to a factory AST and even trying an overflow tank with ast delete. I bought the car with an ast delete and NO overflow tank and NO spring cap. after correcting this with an overflow tank and/or AST My symptoms are that my overflow tank just never stops overflowing. It slowly all leaks out while driving and I hear boiling water and bubbles upon shutdown. I have pressure tested the cooling system, and the results were both no leaks external or internal (overnight). Pulled plugs, bone dry and didn't lose one psi of pressure. I even hydrocarbon tested my coolant for the presence of exhaust gas (coolant seals) and passed with flying colors.. and as per the reccomendation of Cam at Pettit, I held 5psi with a pump to the filler neck and cranked my car. He said his method for testing cooling seals the pressure would build/jump to 10psi+ as exhaust would pressurize the system. Again, I passed with flying colors. I have tried deleting the ast with the black nipple neck to overflow, I even tried adding an AST, tried multiple pressure caps with no luck. No white smoke, no hesitant starts EVER, hot or cold, and no internal or external coolant leaks. I'm so lost right now. Please anyone help !

FD3Cam

Gurgling/bubbling sounds after shutdown are totally normal. I had the same thing and it freaked me out at first but I read that it is simply remote areas of coolant boiling due to the water no longer being circulated within the cooling system.

DaleClark

iTrader: (55)

You may just have air trapped in the system. Get a Lisle funnel -


and use that to fill the system.

With the stock AST setup, you have a radiator cap at the thermostat housing by the alternator and another radiator cap on the AST. Stock, the cap at the thermostat housing is a "flat" cap, no spring. It's just for filling the system. The AST has a cap with a spring, and is rated around 14psi.

The hose from the overflow tank to the AST nipple HAS to be air tight, no tiny pin holes. If you have holes, the system pressurizes, pushes excess coolant to the overflow tank, then can't create vacuum to suck that coolant back in, so it just continually pushes and pushes into the tank until it barfs out everywhere and you have air in the system.

Might want to post a pic of how you have your AST set up as of now.

Dale

gracer7-rx7

iTrader: (16)

Might want to post good pics of your system and maybe a video of what you are seeing / hearing.

cr-rex

iTrader: (114)

is this is whats happening then listen to dale

Whitetiger777

iTrader: (1)

Water pump going bad maybe??? Is there anything blocking air from going across your radiator?

fd3stiny

iTrader: (4)

Hmm that's interesting. My temps aren't overheating but I can actually see the distilled water bubbling/boiling in my overflow tank.. BUT when the motor cools the vacuum draws it back in perfectly. No loss of coolant.

fd3stiny

iTrader: (4)

No blockage in the radiator it's an aftermarket aluminum and I'm running no thermostat. I have been told my apexi 5 inch thick front mount intercooler in front of my radiator might be the culprit. Along with having no belly pan due to this set up causing higher that usual temps- but my temp gauge is dead center

fd3stiny

iTrader: (4)

Ok I will get pics tomorrow. And yes I have used that funnel and it does work however I still hear that bubbling gurgling sound and I can actually see my water boiling in the overflow tank- but it does not overflow. I think it did that to me because I over filled .. I will note that although the water is visibly bubbling and boiling slightly in my overflow- it is not overheating on my temp gauge. It always stays dead center. Also the vacuum upon cool down does suck all the coolant back in, and the level is always all the way up to the top of the filler neck.

Whitetiger777

iTrader: (1)

From what I understand, and anyone is free to correct me on this, but out water temp gauge is a linear based gauge based on the ecu. From what I understand it might not be all that accurate which is why people get external water temp gauges. I have heard from a number of other FD owners that they had to get rid of their FMI when they live in warmer areas because it reduces airflow across the radiator. I've also heard for people have problems who switched over to a 99 spec bumper without getting the uder tray as well. I'm not saying these are your problems but they might be contributing to the situation. Also have you considered maybe your water pump is going bad so the water isn't circulating through your system like it should? I'm not saying these are the problems, just trying to throw out ideas of things to check out.

adam c

iTrader: (2)

If you have the stock temp gauge, you may be overheating, and dont know it. The stock gauge wont go up until you are well over 230 degrees, which is overheating.

You need a belly pan to force air thru the radiator. This is a must!!! You likely are overheating with your current setup.

fd3stiny

iTrader: (4)

Ok, I was under the impression the belly pan would only be the culprit at high speeds overheating. Do you happen to have or know anyone who has a spare in good condition for sale? Oh and will I be able to mount it with my aftermarket fmic and aluminum radiator? From what it looks like, my radiator isn't quite as angled as an oem unit would be

mdp

If you have a 30/70 coolant mixture with a 13 psi (0.9 bar) cap, 230 degrees F is not over heating, the boiling point is 246 degrees F. At atmospheric pressure, which it is without the cap, and is what the poster is testing, the boiling point is below 230:


Figure 1. Boiling Point of antifreeze and water mixture at atmospheric pressure.

So there is boiling going on with the cap off, it occurs on all our cars with a water antifreeze mix below ~60%, the cap off, and the car idling. However, this is referred to as "micro boiling" within the water jacket of the engine, as soon as the coolant moves to a cooler spot in the coolant path in the the small vapor bubbles are reabsorbed and everything looks normal when the coolant gets to filler cap.

This is incorrect, the gauge response is not linear. Here is a link to my article on gauge linearization (good God, I wrote that paper 18 years ago!). The Big Fat FD3S Cooling Thread has the temperature response for the stock gauge.

Now on to fd3stiny problem. I've seen similar symptoms a few times and often it is a very stubborn section in the cooling path that won't properly purge. My theory is this can occur when "crud" (a technical term) builds up in just the right spot in the coolant passages to prevent the air from bleeding out of the section during a gravity fill. The end result is, you think you purged the system, but somewhere you've got a section with air that can't escape, hence a very hot spot causing vigorous boiling which shows up in the filler neck.

So, try this, clean and reverse flush the cooling system (use a very mild cleaner). Refill the system, with the heater on high etc. and the hose going into the throttle body disconnected. When the coolant flows without bubbles out the throttle body hose connect it and continue to fill with your fill funnel.

adam c

iTrader: (2)

230 degrees is certainly overheating, whether water is boiling or not. You dont want to be driving around for any length of time at that temperature.

PM fritz flynn. he will likely have a good condition used belly pan. I dont know how well it will fit with your setup.

oneflytrini

iTrader: (1)

Listen to these guys homie. Plus search for a belly pan. It helps in normal day to day driving, not only highway.

-Ali

fd3stiny

iTrader: (4)

I think you were onto something. I want to update everyone here:
After repeat attempts at burping the system, lisle funnel, and several drives and warming/cooling the motor- my water is no longer boiling, bubbling, or any odd sounds after shut off. I think there was just really stubborn air pockets in my system. Granted I still feel although my stock temp gauge isn't indicating overheating- common sense tells me to get a belly pan and I've discovered one of my fans (turbo side) is barely on when hot or cold. I would like to thank everyone for their input and advice- and that video that was linked to me in this thread was spot with my issues.
Amazing how many symptoms I had that resembled a blown coolant seal but in fact wasn't. Hopefully this thread will help someone in the future.

RCCAZ 1

iTrader: (10)

One other thing worth noting is that when you have the Lisle funnel on and are running the car to try and remove air, I believe it's important to turn your car's heater ON with the temp set to FULL HEAT. This step ensures that your heater core purges any air that might be trapped as well.

Just FYI!

Edit: Oops, say the MDP mentioned the same thing. My apologies!

gracer7-rx7

iTrader: (16)

Happens often. I suspect this is the most common misdiagnosis.

mdp

Glad you had a happy ending, I would recommend either linearizing the stock gauge, or using an aftermarket gauge to monitor engine coolant temperature and definitely get the belly pan.

One more note, for completeness, coolant temperatures in the engine will vary by location, hence the likely source of the dust up with Adam since neither of us specified the location where we were monitoring engine temperatures. There are three places on the engine where temperatures are monitored, the dashboard gauge transducer, the ecu transducer, and the usual spot just below the filler neck where most folks install an aftermarket gauge transducer. The hottest location is the dashboard gauge transducer (Mazda engineers located it at this critical spot for a very good reason). It is located at the end of the coolant passage that passes between the leading and trailing spark plugs of both rotors (third passage up from the bottom on the spark plug side of the rotors:



This spot is the highest coolant temperature location inside the engine. The ecu temperature transducer (whose temperature is displayed by the Datalogit for those with PowerFCs) is in a cooler location giving a more average coolant temperature. My limited experience is under normal driving conditions it is typically 5-15 degrees Fahrenheit cooler than the dashboard gauge temperature transducer. The third location just below the filler neck has been reported to be slightly cooler than that. There are engineering reasons why Mazda selected the first two locations used rather than one spot for reading the coolant temperature. The dash gauge and warning light is supposed to give an early warning of engine over heating. This location responds most rapidly to excessive engine combustion temperatures. The second location is used by the ecu to determine the over all temperature of the engine in order to set the many variables dependent on engine temperature. One final note folks just using an aftermarket gauge should keep in mind that they will not get as rapid a response to excessive combustion temperatures as they would if the aftermarket transducer were located in the same spot as the stock dashboard gauge transducer.

fd3stiny

iTrader: (4)

I will definitely be upgrading my stock*guage!

Fritz Flynn

iTrader: (263)

Be sure the lower port/tube thing on the radiator isn't blocked which will work great for an AST delete car but not so good if you went back to an AST.

fd3stiny

iTrader: (4)

It's an aftermarket aluminum radiator

KehoeAutomotive

Yeah.... Dale is so clever it's freaky. That's why I send him my left over RX7 parts. I plan to go to Florida and buy him all the beers he can drink.

For the last two months I've not been able to work on any of my stuff due to family sickness and death.

Now that I'm back, I plan to finish fixing the cars and heading down to pay homage properly. THanks again Dale.