1986 S4 NA manual trans. Car runs like a bat out of hell.

At the start the coolant bottle is at cold mark. After heat soak the bottle will fill about the normal amount to the hot mark but never pulls it back. Top off the radiator after it cools. Next trip it will do it again until it fills and overflows the bottle.

Have replaced the thermostat and radiator cap w/genuine Mazda parts.

Have burped and bled radiator more times that I can count. Have cleaned and backflushed system. There is no air in the system!

Have tested the following:
1. Tested cooling system w/Stant Pressure tester at fill neck. Holds pressure for 2 minutes per instruction book. Adapter is a bitch to use! Overflow hose holds pressure for 2 minutes. Has clamps on both ends to make sure there is no air leakage.

2. Compression is good (within factory spec using Mazda RX7 compression gauge)

3. No smoke on start (black, white or Blue).

4. No churning of any type when the car is cranked w/fuse out or started, with the radiator cap off.

5. Water temp in radiator when at running temp is ~180-185 degrees.

6. The temp gauge stays at about 1/4 range (Yes I know thay are inaccurate. It is a relative reading only)

7. The low coolant light tests normal but doesn't come on either driving or sitting.

Thought of putting ultraviolet dye in to spot any potential leaks but I think I have proved there aren't any.

Can a vacuum gauge be hooked up to the overflow spout on the filler neck to measure if it is trying to draw anything back? Not sure if it will work with liquids.

Need any ideas of where it could be leaking or how to isolate it to that point.

Tnx Fred

 

Go to NAPA (I think) and by a hydrocarbon test kit. I think you've probably got a blown coolant seal.

 

I see 2 possiblities.

1. The overflow cap and down tube may have a crack

2. The new rad cap may be bad or it is not seating properly

 

There is still a leak somewhere if the cooling system is not recovering from the overflow, period.


-Ted

 

Title says it all, pin hole leaks don't weep much coolant they just pass air too easily back into cooling system when the engine cools down. Thus keeping the coolant from being drawn back from the overflow reservoir. Air in cooling system then leads eventually to overheating and then goodbye coolant seals. Just use the UV dye and do a good visual also. The slight dampness from a pin hole can usually be seen if you're checking carefully.
Good Luck
Gerrard

 

I agree with Gerrard. Are you sure the over flow tube is not pinched or cracked or restricted some how?