a10beav

My stock '99 Firehawk is losing coolant, but I can't find any leaks. After a 3 hour drive I had to add about 4-5 ounces to the tank and after driving around town the next day, I had to add about 9 ounces. The oil looks normal, but I had a leak-down test done and they couldn't find any leaks. It passed a radiator pressure test as well. I've already checked the line under the battery to the reservoir and it's good. The reservoir stays full, it's the radiator thats losing fluid. The car only has about 38K miles on it and hasn't been run too hard.

The two times I checked the coolant was after letting it cool down, so I let the car warm up in idle to look for leaks when it was hot. I still didn't see anything, but I did smell a little bit of coolant. I did notice the fans didn't come on though, but the temp gauge still showed about 200; it never got any higher than that. I think the temp had to get hotter than that with the fans off, so am I loosing coolant because it's overheating? Would it escape through the radiator cap?

I found a few related threads on here, but they had other issues or they never found the problem.

Spartan7

iTrader: (7)

Could be a pinhole leak in a hose, bad radiator cap, or even a small crack in the radiator side tank.

ddnspider

iTrader: (26)

I had this issue awhile back. I was SURE I couldn't find the leak and it MUST be going into the combustion chamber. If you are SURE that you're radiator/hoses aren't leaking, then it's really only going 2 places:

A) The combustion chamber.
B) its leaking out of the overflow that you said you checked.

If you pressure tested and it was good, then my bet is B. I had a pinhole leak where the metal fitting turned to rubber hose that goes to the overflow tank. I would highly recommend adding the ultraviolet dye to your coolant. I couldnt find the leak until I did that.

TransAmBlue

Two places i've found these cars leak at are the water pump gaskets and the hose connections at the water pump. It will leak cold then stop as it warms up. Might be worth checking carefully.

wssix99

iTrader: (5)

Where are you checking the fluid level? If at the radiator, you could have a bad pump injecting air into the system.

a10beav

Thanks for the replies. I've been checking it cold at the radiator and then checking the reservoir. The radiator is low and the reservoir is full.

I hadn't thought about adding dye, so I'll do that next. If it's a pinhole leak, then wouldn't it be obvious when the fluid is hot? I didn't see anything when I let it warm up. Hopefully the dye will answer that question though.

SNLPerformance

iTrader: (15)

Just a thought, Heater core?

wssix99

iTrader: (5)

The same thing happened to me.

If the radiator is low and the overflow is full, there are only two things that can be going on:
- You have a clog in the overflow line and can't hold suction between the overflow tank and radiator.
- Air is getting in to the system at a rate where the car can't self bleed it out.

If your overflow line is good and holds suction, then you must be getting air in. If you passed a compression test, the most likely culprit is the water pump. A few of us have seen the seals go bad in the pump, allowing it to inject air in to the system.

You might check the weep hole on the pump. (It's a challenge - I could only see mine when I got it off the car.) If its weeping and the seals are bad, its time for a new pump.

a10beav

I don't think its the heater core, since the carpet is dry and I don't smell it inside. I'll get some dye and look at the water pump. Thanks for the ideas!

mr.beachcomber

Going for the dye is a smart move. One area that has surprised me in the past is the mating area between the lower radiator hose and the water pump. Seems like as the hose aged over the years on a low mileage car and took a set, the worm-drive clamp needed to be tighten to completely seal the hose against the water pump inlet. Took forever to find that leak! Just a thought...

Good luck finding the leak!

wssix99

iTrader: (5)

Unless there are multiple failures in the system, there is no leak. If there was a leak, (assuming the overflow is working properly) then the overflow would be dry.

To solve this problem, a different mindset is needed. Instead of looking why coolant is "missing," we need to discover why gasses are being injected in to the radiator.

TransAmBlue

Not true...the overflow can be full and the rad emtpy. All it takes is a leak thats present cold and seals when the engine is hot. Engine cools off.....leak path opens......no coolant gets PUSHED back into the rad.

YES I said pushed, the coolant in the overflow gets PUSHED back into the rad by atmospheric pressure. If the pressure in rad is EQUAL to atmospheric pressure<because of the cold leak> no coolant returns and the result is a full overflow and emtpy rad.


I'll say it again......its very common for the water pump gaskets to leak COLD, then seal up tight as the engine warms up. Overflow will be full and the rad empty. I seen this about a 1000 times.

Another place to look is at the factory hose clamps. They get weak over time and will let coolant leak out of the ends of the hoses cold as pressure starts to build in the cooling system. Once warmed up the hoses seal and no leak is found....only seen this about a 1000 times too.

This results in a full overflow and empty rad.


PSSSST your 99 Firebird has the problem WATER PUMP GASKETS in it from the factory. GM updated them because of this VERY PROBLEM.

CHANGE them to the updated gaskets!

wssix99

iTrader: (5)

If the OP had this, then their pressure test would have shown it.


All of this would show up on a pressure test.

As well - if this theory were correct, the air in the radiator would be pushed out in to the overflow tank during each heat-up cycle of the car and excess fluid would be pulled out of the overflow to fill the radiator back up during cool-down. Presumably, the cool fluid would leak out again. Over time and several cycles, this would lead to an empty overflow tank.


Atmospheric pressure doesn't cause anything to happen - pressure differentials do.

As the coolant heats, it expands. As the pressure from this expansion increases, the cap on the radiator allows the pressure to bleed off through coolant flowing to the overflow.

As the coolant cools, it contracts. As the vacuum from this contraction increases, the cap on the radiator allows the vacuum to dissapate by sucking coolant back from the overflow.

7camaro7

iTrader: (15)

Pressure test the system, nuff said

a10beav

It was tested and it passed. It also passed a leak-down test.

I haven't had time to work on this yet, because I had to leave the car in another city. I didn't want to risk damaging the engine if it was getting in the oil. Hopefully I'll be able to check it out this month and I'll post if I find the culprit.

Thanks for the ideas.

a10beav

I couldn't find any radiator dye, did you use the stuff for air conditioning tests?

I've looked the car over again and I still can't see anything. I put the car on a lift and let it heat up and cool down, but no leaks. Nothing from the hose ends or the water pump. Even though I couldn't see the weep hole, I didn't see any fluid dripping from the pump.

The oil on the dipstick looks normal, but do I need to drain it to look for discolored oil? It would be like chocolate milk if it's getting in the engine, right?

I did confirm the fans never turned on when the temp increased, but they work when the a/c is on. The temp gauge never leaves 210, but I'm wondering if the engine is overheating and maybe I'm loosing coolant as steam? It gets to normal temp in 5 minutes, so they gauge should have increased more after letting it run for 10-15 min, but it never did. The fan fuses are good and I changed the relays, but they still don't come on. The temp sensor should still be good since the gauge is working, right? I'm thinking I should solve this fan problem before doing any more on the engine.

BTW - on my last test, I filled up the radiator and let the engine idle for 10-15 minutes. In this timeframe, the coolant level dropped 3-4 inches in the radiator and the overflow tank is still full.

Just a reminder, it passed a leak down test and a radiator pressure test.

anheuserbusch08

iTrader: (11)

lemon. that is all.

wssix99

iTrader: (5)

If you don't have a leak, dye won't do anything for you.


Then you definitely don't have a leak.


It doesn't gush. It "weeps" very slowly. Any leaking coolant can dry up before it hits the ground.


You want to check the dipstick on your overflow bottle. (not the engine) You shouldn't have any oil on it at all.



If you are loosing fluid, you'd see it. If you were boiling the fluid, you'd see water vapor.

You've done all the tests and your results are not pointing to a leak or escape of fluid. All signs point to an injection of gas/air in to the system.

a10beav

Thanks for the answers. Would it get air from a bad radiator cap?

wssix99

iTrader: (5)

You get it from a bad water pump - just like I did. The seals went bad and air was getting through to the impeller. Its very odd - unlike anything I've seen on other cars. It happened to me and a few other posters. Its also about that time - 10 years-ish where rubber seals, etc. are starting to go bad on our cars...

I was altered to the problem by a bad coolant level sensor. (I'm so glad that I kept the thing hooked up!) I went through all the tests you did and ruled out all leaks and proved that my overflow worked fine. By process of elimination it had to be the pump.