Cooling System Troubleshooting

Last updated: April 19, 2000

Date: Wed, 19 Apr 2000 12:26:51 -0700
From: "Ulen, Robert S" (

The coolant overflow tank dipstick should have many small slots in it. When the slots are covered by coolant, and the dipstick is removed, the coolant should remain in the slots. The level is as high as the highest slot that contains fluid.

If you pour too much coolant into the overflow tank, it will start coming out the tank vent which is high on the tank. In that case, you have too much coolant in the overflow tank. If coolant drains out of the tank when you first pour it in, chances are the main hose is disconnected on the tank (hose that runs to near the pressure cap for system venting). The overflow tank holds much less than a gallon.

Check the level in the overflow tank when cold. I like to run mine on the "F" mark when cold. When the engine is fully hot, the level will rise about 2 slots on the dipstick. The best way to check if the radiator is full, is to open the filler neck cap on the engine (ONLY when cold) and see if the level is within 1/4 inch of the top of the filler neck. If not, add coolant.


Date: Thu, 23 Sep 1999 10:08:46 -0500 From: "Eng, Cary" (

>Yesterday morning I got in my car to go to work, after the car reached
>operating temp  noticed a few wisps of steam coming from the right side
>of the hood. Pulled over immediately and popped the hood and there were
>a few more wisps coming from just behind the pipe that comes up from the
>bottom of the intercooler. It was coming from underneath that pipe where
>it is closest to the intake manifold before turning and going down
>again.. Could find no drips or wetness anywhere and it didn't do it
>again.  May have been a total coincidence but the bits of steam started
>right when I turned the heat on. It did the same thing this morning and
>stopped right away. My temp guage did not budge from where it always is,
>just down from horizontal.
>Seems like it would be tough to troubleshoot with no wetness but I also
>don't want something to fail big.

There's 4 possibilities here. All of them require you removing the the front plastic intake pieces, intercooler, and air filter box. Not a huge chore or anything since it all comes out pretty easy. Anyway here are the 4 areas to check:

  1. Lower radiator hose. This piece runs from where the water filler cap is, down to just under the lower intercooler pipe. Check the condition of the hose and its connection.

  2. Check the small (1/4" maybe) coolant hose coming off the water pump housing. It's located right by where the lower radiator hose attaches to the water pump housing, but it runs back toward the firewall (not sure where it goes to). If that leaks, coolant will probably drip down the lower radiator hose.

  3. Air seperator tank (AST) overflow hose. This is the hose that runs from the AST all the way across to the coolant overflow tank by the passenger side headlight.

  4. Water pump itself. Might be the gasket where it mates to the motor. I'd check the hoses first because changing the water pump and gasket will take a few hours. It's a simple task, but it's not an easy task. Well not for me anyway :-)


Date: Sat, 25 Sep 1999 15:29:36 -0700
From: Max Cooper (

If the steam you speak of was coming from where the y-pipe and the plastic "cross pipe" connect, it is probably the coolant hose that goes to your turbos.

I replaced mine on the side of the road not so long ago after it burst open. It blew out a 3" slit in the side of the hose and lost a lot of coolant. The hose was deteriorated to the point of being just a black sloppy mess.

To get to it, you need to remove the air pump. I removed the upper intake hose and the cross pipe to get in there. Then you can unplug the air pump and take out two bolts to remove it. You may have to pry it out where it connects at the top, but it is easy to pry with a pry bar or the end of a wrench. With the air pump out, you can see the hose right there. It is about 3/8" ID, and the stock one has a black foam cover on it. Replace the hose and reinstall everything. You may need to bang the air pump back into where you pried it loose. Just line it up and drive it in there, using something to drive it so you don't put hammer marks on the air pump.

I recently had a coolant leak much like you describe and it turned out to be that same hose. I used worm-screw type hose clamps when I replaced it, and they had worked themselves loose. It isn't a big surprise considering the extreme heat cycling that they are subject to, and the similar problems with the big hoses using the same type of clamps. I tightened them up and squirted a little threadlock onto the threads. It took less than one hour this time from hood open to hood close.

You will be better able to tighten the clamps at the y-pipe / cross pipe connection with the upper intake hose removed, too.


Date: Fri, 31 Mar 2000 08:12:29 -0700
From: dbeale (

>My car slowly looses coolant, and it appears to be leaking out of the
>overflow tank, yet the tank is full - what's up?


>My car "boils" around the turbo area when I shut it off, even though 
>I let the car idle/drove slowly for awhile before shutdown.

You have a "vacuum" leak in either of the caps or one of the lines that go to/from the AST, or one of the lines is pinched shut.

When the car cools down, it generates a vacuum that pulls coolant from the overflow tank back into the engine. If you have a slight vacuum leak this doesn't happen. When you start a cold car, it pumps a bit of coolant into the overflow tank as it warms up and the coolant expands. Note that this slight vacuum leak will -usually- not leak coolant under pressure.

The result of all this is you gradually overfill the overflow tank and it leaks where the filler neck joins the main body of the tank (the filler neck just sits in there with a "gasket" supposedly sealing the joint - it doesn't).

The fix - replace both caps. If this fixes it you're done. If not, replace the small coolant lines that go to/from the AST. I recommend using proper "heater hose", which is thicker walled. It resists pinching. I also rerouted the line that goes to the overflow tank. The PFS intercooler tends to sit on top of it if you're not careful. I moved it behind the crossmember, as I recall. This is not an expensive fix/mod. (though the Mazda price for the caps. is a waker-upper).

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