I pulled my FD out of the garage today to let it warm up since I'm not driving it for the winter. It was somewhat difficult to start, but I figured it was just flooded. I finally started it, and it ran a little rough. I let it run for a little bit, hoping it would even out. The idle smoothed out a lot when it ran after a few minutes, but still a little rough. But I noticed the temperature on my Commander was pretty stagnant. After about 10 minutes, the temperature still read around "40". When that happens, I KNOW there is a problem, because it usually happens when there is not enough coolant in the system, but it was topped off completely today. Just as I suspected, when the PFC read "60", the guage on the dash started to head north. When the system is low on coolant, the PFC would usually read around 50-60 for awhile, then rapidly head towards the 100s. But this time, it just wouldn't warm up on the PFC, AND the car began to overheat.

I've searched for months on coolant related issues, because I have been having some difficulties with my system for some time. This is a new issue for me; anybody have any ideas on what to troubleshoot? Right now I'm letting the car cool down, and I'm going to check and make sure there is enough coolant in the system, but I'd like some opinions on what to do if that is not the problem. Thanks! ~A-Rod

 

I don't remember the details of your previous posts. However, rough startup and repeated low coolant levels are possible indicators of a coolant seal problem (as I am sure you are aware). What have you done in the way of past diagnostics?

 

Well I've changed the hoses, but that didn't stop the coolant from disappearing. The thing that confuses me is that everyone has said that if you have a coolant seal problem, your car will probably be undriveable within 1,000 miles... Mine has been having strange problems for about 4. There is still no white smoke in the exhaust (save for startup), I just have disappearing coolant. I was thinking about checking the resevoir tank, but that doesn't seem to be the issue, as it is completely dry.

I read the FAQs in the 2nd gen section, and it suggested pulling the EGI fuse and turning the engine over with the filler neck cap off. If a LARGE amount of coolant is dispersing, the seals are bad. A 3rd gen motor should exhibit the same symptoms as a bad 2nd gen motor, correct?

 

A. IIRC, I have seen 1 or 2 posts about coolant seals failing very gradually, and exhibiting symptoms like yours.

B. A very slow coolant seal leak will not necessarily cause that symptom. In fact, some coolant seals only leak one way, depending on the exact nature of the leak (which side of the seal is not seating correctly, as in the case with o-rings in general). Therefore, you could be leaking coolant into the engine, but not getting combustion gasses into the coolant.

Dave

 

FYI, I drove my car for a months, daily, with toasted coolant seals. It always started fine cold, but the hot starts were more than tricky. The longer I drove it, the more the startup smoke got thicker.

There is not much to the cooling system. There are two things you could look at checking/replacing:

* Water thermosensor
* Water pump

Even if your engine does have toasted coolant seals, it's a good idea to have new replacements of those items.

 

I just (2 weeks ago) replaced the coolant level sensor - it had cracked and was causing a coolant leak.

Dave

 

My car constantly drinks water with no problems whatsoever also and has done the past year/ 6000 miles, i take the filler cap off, brim it with coolant, wait 10 seconds it goes down, repeat times 30 = same, still goes down, but doesnt escape onto the drive and i have no heat problems or white smoke.? mystery hey

 

I think my water thermosensor is no good, it doesn't seem to give accurate readings. Oh, and I completely left this out... my coolant buzzer doesn't EVER go on, even when there is a minut amount of coolant in the system.

What is a ball park price on that sensor? And is that the one that would need to be replaced if the buzzer isn't going off?

 

Nope, the coolant level sensor and the water thermosensor are two different sensors. The coolant level sensor is on the front of the t-stat housing. The thermosensor is on the back of the waterpump housing.

IIRC, the water thermosensor was around $50-60.

 

A. Got the coolant level sensor and the gasket from Ray at Malloy for~$60 total, incl shipping.
B. Yes (the coolant level sensor, as Mahjik said, not the thermosensor) - unless the wiring to it is faulty. There is a check procedure in the FSM.

Dave

 

If your car is low on coolant, the car would not necessarily overheat. The scenario you have outlined sounds like a bad thermostat to me.

 

1. like mahjik, i drove my first FD with a bad coolant seal for like 2 months before it started getting too bad to drive. hard starting, overheating, and disappearing coolant are all add up to a tell-tale sign of a bad coolant seal.

2. with the engine COLD, top the coolant level off, take off the main waterpump/alt belt, and start the car with the coolant fill cap off (the one on the t-stat housing). if there's any movement in the water level or any bubbles, there's a bad coolant seal. you only need to run it for less than a minute.
make sure you do it with the belt off, though, because if the water pump spins, it'll push some water out of the top. with the water pump not spinning, the ONLY thing that could possibly cause your coolant level to change or get bubbly (or both) is the combustion getting through past coolant seals.
when i did this, the coolant spouted out for 1-2 seconds and leveled off. alas, if the coolant level changes at ALL during this test, a water seal is bad.

this may seem like kind of a hassle just to check the seals, but it's definitely worth it to know whats up with your engine.

 

Thanks Adam, I knew I left something off the "go ahead and replace this" list.

 

Here's a link for you to use next time.

https://www.rx7club.com/showthread.php?t=719508

 

A link for the "Linkmeister."

 

I now believe it is a combination of both a thermostat and coolant seals. The disappearing coolant has to be the seals, as there is no leaks under/around the car. Today when I started the car to let it warm up, after it pressurized, I noticed the long hose from the radiator to the filler neck was not by any means hot. So I'm definitely thinking a bad thermostat. But would this cause the temp reading on the PFC and the guage on the dash to be non-linear? Do they use two different sensors?

 

I'm not sure what the PFC uses. If it reads somewhere after the t-stat, it is probably working right. The first thing to do is replace the t-stat with a new oem unit.

You may be able to drive the car for a long time with failing coolant seals, depending on your use. Long trips may no longer be possible .

 

Thanks. I'm going to order a new t-stat tomorrow. I was talking with another member on the forums (good friend of mine), and I think we're going to rebuild the engine within a month or two (or six, lol, I can never get things done in the time I want them to be ready). I figure the first step is to make sure that the t-stat is the current problem, and then go over the car and see if we can find any other flaws from there.

 

Our cars have 4 sensors for the cooling system.

1 coolant level sensor- front of filler neck - you already have that one

2 water thermosensor- backside of water pump housing, removal of alternator makes it easier to access - this sender tells the ECU what the temp is

3 thermoswitch- also backside of water pump housing - controls one of the fan speeds - common mod is to replace it with the FC thermoswitch which trips the fans on sooner.

4 temperature sensor - located on the driverside below the oil filter but above the oil pressure sender, its a really tiny sensor that tells your dash gauge where to put the needle.

Ray at Malloy can let you know which sensor on the back of the housing is what.

Just to clarify when you say you replaced all the hoses was that all 11 or so available from Ray? I use to catch a whiff of coolant mostly after shutting down. After few weeks or so eventually it was another hose I had yet to replace because of a pin hole leak.

If after testing the coolant level sensor you still don't get a sound, there's a little long box located on the drivers side kick panel known as ECU#2 or Flasher Box. It is what handles all the little beeps and buzzes and blinking in the car. Mine slowly went bad until one day the seatbelt warning that never went off from day one wouldn't shut up. Check the continuity from the sensor side to the boxes harness side to eliminate a possible break in the wiring.

Order a mazda t-stat from ray, no after market crap. Also check the pressure cap on the AST if applicable.

 

^Thank you for the detailed information!

So since the PFC readout is controlled by #2, and the dash guage is controlled by #4, a faulty thermostat would be the reason these 2 guages have different readouts.

 

^yes that's true.

Even though most consider #4 to be useless, once I replaced it I had a much more "accurate" reading with my dash gauge. If that sensor has not been replaced, do it. It's cheap, easy, and there is minimal coolant loss.

I personally have replaced all those sensors/switches. I still suspect my PFC reading is off a few degrees from what the sensor is telling it due to an aged wiring harness cooking under the hood. These sensors are electric and if the flow of juice is not a hundred percent you can't expect the same when monitoring the commander.

 

When you say tells the ECU what temp it is, would that cause random bucking or hesitation at low rpms?

Because now the weather is getting warmer (i had this problem last summer), the car would buck and hesitate like crazy when im driving off easy. What i did last summer was pull over when this was happening and let the car idle to about 120F, then the car acts fine from there on out.

NOW, if i shut the car off after a drive, say go to a store and come back, the temp is now 200-205F from heatsoak whatever, i dont even let the car idle because its warmed up already from the drive prior, i just go. I get the same bucking in the low rpms like i had when the car was first cold.

So my question is would this thermosensor be faulty probably telling the ECU the engine is cold and run rich even though i just had a drive and the REAL water temp is 200F?

During the winter when i would take it out randomly, it didnt do this not one bit. So im guessing it has something to do with ambient temp although today it happened and it was only 59F.