darkhawk

Background:
So I get in my FD and turn it on, it about 20 seconds the add coolant light comes on, so I get out and look and all of the coolant is being purged from the AST tank (I think thats what its called). So my dad(mechanic) told me it was the radiator cap, so i go and get an another cap from the mazda dealership, since they didn't have any 18lbs one I got a 16lbs one. Well put on the cap and fill up the radiator fluid and turn the car on and the car immediatly starts heating up. I asked my dad whats up and he diagnoised it to be thermostat not opening up properly due to the air pockets in the coolant.

Main Question:
We live in FL and I was wondering if anyone had ran and FD without a thermostat before? I looks like that the thermostat is pretty simple, there aren't any secondary function to it.


The car is still purging radiator fluid from the pipe that is conected to the top of the radiator but I thinks its a cap issue now, the manual say that the radiator cap has to be above 16.4lbs

Whizbang

running w/o a thermostat is not smart.

LUPE

I ran without a thermostat for 2-3 years. The car simply doesn't get warm enough and you can't get a good tune if you can't control the temperature.

AC LINKS

I would like to know the outcome....Keep me posted

Whizbang

there is potential for overheating.

LUPE

People say that but I ran mine for 2-3 years and it stayed ice cold all the time.

fedupfd3

iTrader: (1)

Running a cooling system with out a thermostat, to keep it cooler is a myth. Don't do it.

Your ast cap is the one with the spring incase you have them mixed up. I had a problem with mine overheating after getting a coolant flush done. I changed the thermostat, radiator, hoses, water thermo sensor and bought new caps from mazda. I put the new caps on in the same locations the old ones came off, it still overheated. I found out the caps were in the wrong places and switched them, problem solved.

Shinobi-X

The AST should take care of air bubbles in your coolant (even though you should properly burp the system to make sure bubbles aren't in there).

Running your car without one will make the car take forever to heat up to operating temperature due to the fact that coolant will be circulating when "cold". When the block is hot it can also cause the car to overheat due to the fact that heat won't be allowed to dissipitate properly, instead just running through the system as fast as its being pumped.

DaveW

The actual cause of overheating when not running a restrictor (thermostat in this case) can be two-fold:
1. too low pressure in block (water pump increases block pressure with restriction at block exit) causing boiling and cavitation and the resultant lack of heat transfer
2. higher flow velocity causing cavitation (lower pressure on the back side of internal obstructions) and the resultant lack of heat transfer.

Otherwise, faster flow will ALWAYS improve heat transfer and keep the coolant throughout the system at a more constant temperature, and that is good for many reasons.

Note that none of this is to suggest that running w/o a thermostat is a good idea. I even use one in my track-only SCCA Formula Continental racecar.

Sgtblue

iTrader: (16)

IIRC, there is a passage that will allow some hot coolant from the engine to by-pass the radiator without a t-stat.

rynberg

Been discussed many, MANY times.....it's a dumb idea all-around.

edmcguirk

When you run a with thermostat, the car will warm up quickly and stabilize at one temperature.

When you run without a thermostat, the car will warm up slowly and then the temperature will wander all over depending on your average load and the ambient temperature. At idle the engine will be too cold and under heavy load it will get too hot.

In addition, without a thermostat there is a danger of water flowing too fast. It's not a problem with "not enough time to transfer heat", it's that the water pump impeller blades will cavitate and inject bubbles into the coolant. The car will definately overheat if that happens.

I would only run without a thermostat long enough to drive to the auto parts store and buy a new thermostat.

ed

dgeesaman

iTrader: (7)

Just to support the consensus, they've mentioned cavitation. Cavitation is not air bubbles - it's actually small water vapor bubbles that immediately collapse back into the liquid water. This happens on the low-pressure edges of the water pump impeller. These micro-implosions erode the surface of the water pump impeller.

So in a nutshell, cavitation eats water pumps, making this bad situation worse.

Dave

scotty305

iTrader: (2)

From what you've written, it sounds like you've got the pressure relief cap in the wrong place. Please read this thread carefully, it should solve your cooling woes.

https://www.rx7club.com/3rd-generation-specific-1993-2002-16/cooling-system-flush-info-441967/


If your pressure caps are in the correct place, and you've correctly burped the system, but your mechanic dad still thinks that the thermostat is a problem, then you should test or replace it. The car is over 10 years old, and a new thermostat is much cheaper than replacing an engine.


-s-

DaveW

And use ONLY the OEM (Mazda) thermostat - there have been many problems related to aftermarket ones.

Bad_Karma7

Someone correct me if I'm wrong, didn't Mazda revise the 16lbs to 13lbs due to the stress 16lbs put on the cooling system?

DaveW

Yes - IIRC it was part of the coolant system recall.

93'roadwarrior

hmmm... i was told somewhere that if the coolant seals are going bad you can actually have exhaust gasses pressuring up the coolant system overloading the capacity of the AST and eventually/inevitably causing the engine to overheat due to the exhaust gases in the system. correct me if i'm wrong... but this is what i've been told before. maybe time for a rebuild? How many miles on the engine?

DamonB

Specifically to make life easier on the hoses.

Shinobi-X

When the seals were going on my last engine, I was losing coolant constantly. I certainly wasn't holding onto enough to overload my AST (aftermarket). I strongly believe my engine would've seen an overheat situation do to lack of coolant period, rather than AST failure causing it.

93'roadwarrior

^ yeah i believe that could and most likely would happen, but what if you have a pin hole leak in the seals? My last engine didn't eat a lot of coolant but the system would pressure up like a mo fo... especially after commuting... i took it to rotaryextreme and had them replace the whole motor because it was high mileage and they said the seals were going bad and that I was indded getting exhaust gasses in the coolant system... what I'm tryna say is... is this really even possible? Has anyone else ever had the same problems? From what i've seen i think it's highly feasible... would anyone like to differ? Any information would be appreciated...

Shinobi-X

Oh, I didn't say it couldn't happen...just what occured with my last engine. I doubt the AST (if it was stock) would've been the source of error.

As for exhaust gas getting into the coolant system, yes it can happen.

93'roadwarrior

^ thanks

PhatManBUD

i only ran mine w.o a T-stat when my coolant selas were blown. that way i cud at least get to school before it even started to heat up =P

Temporary for like 3 months til one day i got fed up w refilling coolant on every drive, and i started ripping out the motor.

darkhawk

Thanks alot for the feedback guys, I am going to pick up a new thermostat this week and see how it goes. I'm praying that replacing it and the AST cap will fix the problem, I don't even want to consider the alternative (Blown head gasket).

Here are some stats on my FD:
94 R2
Miles: ~71,000
Greddy Intercooler
Downpipe
After market ECU (I think it is PMC Purple Box W/controller)
Blow Off Valve