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Replacing Thermostat


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#1
NickR

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I think I need to replace my thermostat sometime soon. The temperature gauge sometimes rises slowly above normal, then suddenly drops to normal. Probably the thermostat sticking closed, right?

No big deal; I've replaced thermostats before in other cars, but........

I can't find the radiator drain plug! The Haynes manual says that some models don't have them, and recommends removing the bottom hose instead. But removing the bottom hose (and replacing it properly so it doesn't leak) looks like it would be a real pain, especially since it's hard to get at.

Am I looking in the right place for the drain plug? Just beneath the bottom hose, through that little square flap in the plastic panel under the radiator?

Does anyone else have a 93 V6 with or without a radiator drain plug?

Or should I just go ahead (as Snailman suggested in an earlier thread) and forget about draining the radiator, stick an old cat litter tray under the engine, since not much coolant spills out anyway when you replace the thermostat?

Thanks.

#2
sublime12

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The drain cock is on the right lower corner of the radiator on the side closer to the engine.
But why drain the radiator just to change the thermostat?(dont bother)

#3
snailman153624

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My '94 has a drain, as did Ken's '93 MX-6. It is on the engine side of the radiator, passenger side, near the bottom.

I didn't drain mine, and maybe a cup of coolant came out :huh: it's the highest point in the cooling system pretty much, so all of the coolant doesn't dump out.

Hell, even if it does, big deal, you were gonna drain it anyway :lol: just have a drip pan ready just in case :ohmy:

#4
snailman153624

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The drain cock is on the right lower corner of the radiator on the side closer to the engine.
But why drain the radiator just to change the thermostat?(dont bother)

Drat, beat me to it :lol:

#5
sublime12

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:lol: B)

#6
NickR

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Aha! Thanks guys. I found it. I was looking on the wrong (driver's) side. It's not so difficult to get at after all. Thanks again.

#7
NickR

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Update: Well, I changed the thermostat. A bit more than a cup of coolant leaked out though, even after I had half drained the radiator. (The V6 thermostat, unlike the I4, doesn't seem to me to be at the highest point of the coolant system).

A couple of strange things though.

I can't get as much coolant back in as leaked out. I have "burped" the system, by squeezing the top hose to get the air bubbles out, run the engine, put the heater on, so I should have got all the air out, but I still can't get any more of the coolant back. Does that red cap on the motor near the top hose which says "do not remove" have anything to do with this? Why aren't you supposed to remove it (except when hot, obviously). What's it there for if you never remove it?

My temperature gauge still won't stay steady. It sits a little bit higher than halfway most of the time, but sometimes, like when I accelerate hard away from the lights, it rises to about 3/4 the way to hot, then drops back. Do your temp gauges do this? Maybe I need a radiator flush? (The waterpump was replaced about 30,000kms ago, so it should be OK.)

#8
Zuke626

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Try spraying the outside of the radiator with water to flush out debris, someone else had cooling problems also & resolved it by doing this. Heres the thread:Clickie

#9
NickR

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Thanks Zuke! I hosed it down yesterday, and a few dead bugs came out. That may have been the problem, since it seems fine now (I also "burped" a bit more air out of the radiator), but the weather's not really hot enough today to know for sure if it's fixed.

I had been following that thread you pointed me to, but not all the way to the final post, where he fixes the problem by hosing the radiator. It just shows the importance of people replying to suggested solutions, and telling the rest of us what the final cure turned out to be.

#10
NickR

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An update on my cooling problems:

It turned out to be an intermittent problem with the main fan. I was doing a long drive in hot weather yesterday, and had intermittent overheating, especially after stopping at traffic lights. (That was the clue that lead me to suspect the fan -- it really only needs the fan when idling or driving slowly.) By listening carefully, I discovered that sometimes the main fan was coming on when I was stopped at lights, and the temperature stayed normal, and sometimes the fan stayed off, and the temperature gauge rose.

(My temporary fix was to turn on the AC, since the compressor is bust, but turning on the AC automatically turns on the secondary fan, cooling the radiator. Less uncomfortable than the other temporary fix for overheating--turning on the heater!)

So now I have to find out why the main fan sometimes fails. Probably a loose connection? Maybe the relay (where is it?), or the sender.

#11
jpit

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I would think it's more apt to be a poor connection like you had indicated. Here's the location of the '97 V6 cooling fan relay. Not sure if it's the same as yours. Also on the '97 model, the coolant temperature sensor is the item responsible for turning on the fan. When it reads a low enough resistance, the ECU takes this as being that the coolant has reached 207 degrees F, it then sends the cooling relay 'pick' signal which allows 12v to pass to the cooling fan. For a '97 V6 the resisitance of the ECTS needs to be less than 300 ohms for this to occur. Like I said before, your '93 may be different. Even my '97 I4 uses fdifferent values. Careful of the Haynes manuals reading. Not sure which car it was written for but definitely not mine!

#12
NickR

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Thanks jpit!

A final, final (I hope) update. I cleaned the connections to the fan and fan temperature sensor, and the problem has not recurred (touch wood). The fans now come on whenever they ought to.

I'm getting the sense that electrical connection problems are often at the root of things, especially in older cars, like mine (a 93 with high mileage).

#13
NickR

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Nope, I spoke too soon. The problem came back again today (when the temperature reached 30Celsius in Ottawa)!

It's definitely a problem with the main radiator fan sometimes (not always) coming on too late, when the temperature gauge is creeping right up towards H.

(My temperature gauge normally reads a bit on the high side, but I think this is just a slightly paranoid gauge, since I replaced the thermostat and it made no difference. When you start the car from cold and drive off normally, the gauge climbs slowly and steadily to just above the halfway point, then stops there. The temperature gauge only climbs significantly above its favourite resting place under conditions when the fan ought to come on (idling, stop-go traffic on a hot day, etc.), but fails to come on.)

I tested the three fan relays in the fuse box (thanks for the instructions jpit) by running a current across 2 terminals and listening for the click and testing for continuity across the other two terminals. They all checked out OK. (I wonder why it needs three relays? Low speed, high speed, AC fan?)

It may be the fan temperature sensor (my 93 has 3 temperature sensors: fan, ECU, and gauge). I took it out and inspected it (a spark plug socket roughly fits, by the way) and it looks OK, but I really need a thermometer as well as my ohmeter to test it properly. Maybe I will replace it if the problem recurrs, but I bet it's only available at the Mazda dealer, at a steep price.

Then, by chance, I noticed a tiny black box, just outside the main fuse box, next to the diagnostic box, which says "cooling fan" on it. When you lift the tiny lid, there is a 30 amp fuse inside!

Why are there two fuses for the fan? There's the 30 amp fuse in the little black box, and another 40 amp fuse inside the main fuse box. Is the first (30 amp) for the wires leading from the sensor to the relays, and the second (40 amp) for the wires leading from the relays to the fan?

I removed the 30 amp fuse from the little black box, and noticed the terminals were slightly corroded. I cleaned things up and put in a new fuse. Would a little bit of corrosion here slightly reduce the current from the sensor to the relays, and cause the relays to "think" that the temperature was cooler than the sensor was saying, so that the relays only turn the fan on at a higher temperature? (The resistance in the sensor falls as the temperature rises, right?)

I then took it for a test drive, and everything seemed to work fine, with the fan coming on when the temperature gauge rose only a little. But it is cooler out this evening, and it was always an intermittent problem anyway, so I can't be sure. But any light anyone can shed on this extra fan fuse would be appreciated.

Thanks

#14
needamazdafix98

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IMHO...you need a new radiator. My car was acting similar to yours, overheating at idle, able to cool by revving engine, etc. I changed the reservoir, flushed the system, changed the thermostat, flushed again, checked the fans, and finally got around to replacing the radiator after nothing else worked. Now, she's cool as a cucumber.
B)




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