Hey there, I'm trying to sort out a couple of cooling-related quirks that my FD has and hoping someone here can help. I'm relatively new to FDs (and RX-7s in general), but not new to cars, so feel free to get technical with your answers. This is for a '93 touring model with a fresh rebuild, Fluidyne radiator, Pettit aluminum AST, and a Power FC.

Issue #1: Low coolant buzzer. It goes off constantly. This started happening randomly when I started it up one day, after a couple thousand miles of breaking in the new engine. Coolant is NOT low. After driving it and checking it periodically, it's fine. I replaced the coolant level sensor (the one on the thermostat housing near the filler neck) and that didn't help. Is there another sensor somewhere?

I was told the coolant seals could be bad, but again, the engine is new. So I was thinking it must be air in the lines, but I've run the car a lot. Shouldn't the AST have done its job by now? Or is it possible that there is so much air that I need to try and burp the car manually? If so, why would this issue have come up all of a sudden?

Issue #2: Power FC commander does not read the correct water temperature. I never had this problem until I got the car back from having the new engine installed. Warm idle temp displays around 25*C, and it never goes over 35*C or so. Could this be a bad sensor too? If so, is it the one on the back of the water pump?

Note that the water temp gauge in the dash reads normal. Any help or suggestions of where to start troubleshooting would be great! Thanks!

 

You need to burp the system manually, after you top the coolant you will have to check up on your coolant levels several times each time you start her up after a drive. Also, stock water temp gauge is too slow in terms of reaction, if you see it go up on the stock gauge that is treading into danger zone and in many cases the point of no return.

 

I had a low coolant buzzer go off all the time for the first five minutes of start up
wouldnt go away until i checked the connection, which was loose. I replaced it.

 

+1 on manually burping the coolant several times. Even if you squeeze air out of the coolant hoses the first couple times, there are still some spots that linger. It helps to remove the coolant line on the back of the throttle body when initially filling the car w/ coolant. A lot of air will escape this way.

 

I thought the coolant temp sensor was in the same area as the low coolant switch is it possible the two swapped into the wrong plugs IE low switch into the temp switch and vise versa? I will take a look at the FSM to double check my thinking

Mike


Edit: Alright after a quick skim through the FSM the thermocouple (temp sensor) is right behind the water pump so only a few inches away from the coolant lvl sensor, check the wires make sure they are not crossed, unfortunately I do not know the wire colours ect. This is where I would start though

Good Luck

 

OK so, bump, because I'm still having this problem. To answer your question MSilk, no they aren't crossed haha.

As part of troubleshooting, I replaced both coolant sensors on the back of the water pump housing...one with a green connector, and another with a black. Pretty sure they are the thermosensor for t-stat control, and the coolant temp sensor, respectively. Burped the system several times. No dice.

Maybe I'm not burping it right? The coolant system on the FD is different from any other car I've owned, with the AST, and the fill spot on the water pump housing, not on the radiator. Is there a good write up anywhere? I just followed the directions on the Robinette site...

"Run the car for a about three minutes (don't drive it yet because you may be low on coolant) and shut it down. Put a rag over the engine coolant cap and open it up, pulse the big coolant hose, and top it off. You will need to do this several times. The first time you drive it take some water with you because you may get the "Add Coolant" buzzer and you don't want to drive the car for more than about 30 seconds with the buzzer on. Remove the radiator cap and top off the coolant level before you drive the car for the next three drives and you will have a well purged coolant system."

So here are my next questions:

- Where does the ECU (Power FC) get its reading from for water temp? Someone mentioned there is another temp sensor on the back of the block, could that be it?

- If it is absolutely the temp sensor on the back of the water pump housing, then something must be bad in the wiring...how can I test to make sure the sensor is getting the right voltage?

- Is there any way to troubleshoot if maybe a connection on the ECU is bad?

Thanks again all.

 

the sensor that the ecu reads the temp from is not the one on the back of the t-stat housing, check the FSM I'm not sure where the one the ecu reads from. Also in the FSM you can find a pinout of the stock ecu and you can figure out which wire it is, it's may be loose at the connector to the ECU. The ECU is located under a panel on the left side of the passenger foot well.

 

Definitely sounds like some wires were crossed. Coolant temp won't ever be 25*C for long. Most likely it is either erroneously connected to the air temp sensor or fuel temp sensor. I forget exactly where the coolant sensor used for the PFC is but it is toward the rear of the motor. IIRC, I believe it is over around the oil filter somewhere. Download the Factory Service Manual from the sticky links and find it there.

The FSM will have the test procedures and voltage/ohm specs for testing the various sensors.

As for getting air out of the coolant system, search for "Lisle" or go to the FAQ thread stickied in this forum and go down to big fat coolant system thread and read it. It has a link to a video of a Lisle being used to purge air out of the coolant system. It can be a pita to get all the air out but the Lisle works very well.


Good luck.

 

hi there, how full is your overflow talk? what im getting at is, does the engine suck the majority of the coolant from the overflow tank back into the engine when it cools down?

does your coolant level alarm stop going off after awhile? i know you said it goes off constantly but how long have you run the car for while its going off?

check the connections from the ast to the overflow tank.

edit: ill add some on burping the coolant. Add coolant, start car, crank your heaters on full. Let the car run untill the thermostat opens. Shut off car, let it cool, add more coolant, repeat.

best of luck to you

 

Actually, it is. 2 pin green connector.

The other "sensor" on the back of the t-stat housing is actually a switch to bump up the fans another speed.



I've never had much difficulty refilling my system properly, as long as the car is level and the hose is off the TB. This sacred-voodoo-dance-of-a-thousand-hose-squeezes business is nonsense....unless you've grossly perverted the stock setup with something like a FMIC.

I suspect the OP may have a broken wire somewhere. The coolant level "sensor" is nothing more than a means of terminating a wire in the coolant. When there's coolant at the end of the sensor, the circuit is grounded and the buzzer is OFF. When there's no coolant, there's no ground and the buzzer is ON. The circuit is actually being completed THROUGH the coolant.

If there's a short or break in the harness somewhere, the buzzer isn't getting a ground signal so it buzzes.

 

Thanks again for the replies. I did check the FSM before posting this, but it's not very helpful---the only thing I could find in relation to this is on page E-16. Not only is that diagram massive and hard to decipher, from what I can tell, it only shows the thermoswitch, nothing about the other sensors. I can't find anything related to the ECU, either. Am I just not looking in the right place, or what? I will try taking some pictures of how the wires are connected tonight...maybe someone can tell me if it's hooked up wrong just by looking.

If it is truly the two-pin green connecter on the back of the water pump housing that reads the water temp, then it's not the sensor, so there's probably a short in that wire somewhere. Great. I'm starting to think I should just replace the whole damn wiring harness...it's not in great shape anyhow.

 

I actually didn't check the overflow tank...I'll do that tonight. If the overflow tank isn't full, would it cause the buzzer to go off? I thought it was simply based off coolant level at the filler neck.

The alarm NEVER stops, even after driving. Doesn't matter how long you run it.

Connection from AST to overflow tank is fine...no leaks or anything there.

And the heater doesn't work But other than that, the process you described is pretty much what I did.

 

It is a TWO WIRE SENSOR on the back of the waterpump housing.

They can go bad. I've seen it multiple times... the reading will be incorrect, either too hot or too cold. All the info you need on the ECU's water temperature sensor is in the fuel and emissions control section of the factory service manual. As a rule, just about anything having to do with the ECU or the fuel injection system will be in this section of the manual.



You have a Power FC, so go to etc--> sensor/sw check:



If there is an open circuit the "WTRT" will be highlighted. The diagram immediately above can be found in the instructions for the Power FC as well as my thread about the Commander https://www.rx7club.com/3rd-generation-specific-1993-2002-16/how-make-your-untuned-pfc-basemap-safer-idle-better-no-datalogit-needed-841706/

If you are going to pull the sensor out, you might as well just replace it and not even waste your time testing it. If it doesn't fail now it will fail eventually. Mazdatrix has the OEM one for $42. http://www.mazdatrix.com/getprice.as...m=18-8400-NF02 or you can call Ray Crowe at Malloy Mazda (forum vendor). I don't think the crush washer is listed on the Mazdatrix site, but you could call them up and order that too.

Also verify that you have the water temperature plug connected to the water temperature sensor and not the fuel temperature sensor.

 

Note the difference in wire colors for the water temperature and fuel temperature sensor harness plugs:



These connector diagrams can found in the Engine Control System section of the factory wiring schematics which widely available online. If you don't know what the color codes mean, the answer to that is also in the schematics. The answer to most of your questions can be found somewhere in these widely available documents, you just have to know where to look.

 

Wow, thanks! OK, so off the top of my head I can say a few things.

1) I did check the PFC for the WTRT voltage. As I recall it was right around 2.5 when the car was hot. I'll double check that tonight.

2) I did just replace that sensor.

3) Based on the description of the wire colors, it sounds like the fuel temperature plug may be connected to the coolant temperature sensor. The wires are both brown, I can't recall the secondary colors, but there is definitely NOT a green and white wire on the plug that is connected to the CTS.

And I definitely did NOT know where to look I will see if the plugs are reversed tonight. Thanks again!

 

sometimes I think argh has the fsm memorized

 

^ photographic memory son

 

The temp sensors WERE reversed. PFC now reads the correct temps, car runs a lot better obviously.

Still have to figure out why the add coolant buzzer is going off, though. I'm guessing that one actually IS a wiring problem.

 

yay, one less problem

 

If I remember right, the add coolant buzzer gets its information from one of the doo dads on the water pump. From there, the wire goes over to the driver's side near the oil filler where it connects to the next harness in the chain. This is a single ummm black (I think) connector.

Try looking for a black connector near the oil filler pipe/power steering area which is loosely connected to the next harness.

Again this is kinda from memory.

Try reading this short thread.... see if it helps.

https://www.rx7club.com/showthread.p...highlight=wire

 

I actually just finished a little work under there and the coolant level sensor is a white connector on top of the t-stat housing that connects to the emissions harness. The dang thing is mounted there so there.s not much of a chance of it getting lost. From there it kicks back to the ECU, but off the top of my head I'm not sure which pin it goes to. It essentially works as if its grounded, it reads its fine, but if its open then you have problems. If you followed the coolant system burp instructions correctly then its probably just a broken wire in the harness (FUN!) and you can either pull the whole harness and trace it, or you can redneck it together and just run a new wire from the connector on the t-stat housing to the proper pin on the ECU. Check the wiring diagram for the correct pin.