Radiator Cap-- Should I hear a hiss?

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I've been trying to locate a coolant leak in my SL2. It's a 96 with 121,000 miles. I've added about 24 ounces of coolant to it over the last 8 months.

I do not see any visible leaks, nor do I see any oil in the coolant or coolant in the engine oil.

However, today I unscrewed the cap on the pressurized surge tank immediately after an 80 mile highway drive. I didn't get any hiss while removing the cap.

Is this a bad thing? Could it be that my system is not staying pressurized? Would this explain my coolant loss?

Thanks.
 
I am not an expert on this but I will give you a few thoughts, I do not think the cap is the issue, the coolant has to be leaking out somewhere or going into your oil.

It could be a minor head gasket leak, meaning the coolant loss is so minor that it is not showing up in your oil.

I remember when the Chevrolet Vortec motors were loosing coolant and there was no visible coolant loss, it was later found to be escaping out of the intake manifold and running down the back of the engine where it hit the exhaust pipe and then evaporated.

Have you thought about going to NAPA or CarQuest and buying the dye that you put in the coolant to see if there are any leaks, this will show up with a UV light.

I would also check all of your hose connections too.

Is this car a Saturn or a Mercedes, since I am not sure what an SL2 is.
 
Originally Posted By: c3po
Is this car a Saturn or a Mercedes, since I am not sure what an SL2 is.

It's a Saturn.

According to the experts over on SaturnFans.com, they said that headgasket problems are extremely rare on the DOHC version of the 1.9L engine, which is the one that I have. Instead, they said that I should check for cracking of the radiator near the transmission line area. I checked that area, and mine is bone dry.

I made an appointment to have Pep Boys pressure test the cooling system tomorrow, so I'll see what they come back with.
 
If you had a crack by the radiator you would see some sign of a coolant leak, just my thought.
 
At that age on my SL2 it was the water pump that leaked first. But in my case the pump seal gave way all at once. I doled out the work and they did a pressure test first to confirm it was the water pump. I was loosing some coolant, but not as much as you are until the pump seal went south. Also, I have been told by the knowledgeable members at Saturnfans to check the coolant when the engine is stone cold. If you check it hot vacuum may collapse radiator hoses and some think may contribute to the passenger side radiator crack when the coolant cools.
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Also, I have not seen a single drop of coolant on the ground. That's the annoying part, this leak isn't very obvious.
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On my cavalier, it would only leak from the pump when I left it open, with out the cap. When the pump on it went, before I figured it out, I broke the cap or something and had to wait until morning to buy a new one. I lost about half a gallon of coolant out the water pump that night... Never noticed it leak before that, just had to add small amounts occasionally. That episode is what got me to investigate where it was coming from.
 
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less than a quart of antifreeze in 8 months.?.

I'd take a wait and see attiude on that one..

I've alwasy been of the opinion that since the major component of antifreeze is water, some evpoaration can be expected.although a cooling system is somewhat sealed, its not sealed in the sense of an air conditioning system so some loss is normal overtime..
 
It could easily be... the cap! If it won't hold pressure you'll get more evaporation.
 
You should be hearing the hiss when you open the cap. It looks like you have a leak somewhere.

You can check for pressure in the system by squeezing the top rad hose, you will definitely feel the pressure there.

What I do is I tee into a heater line and pressurize the cooling system to 13 psi with compressed air and then see if the system can hold the pressure. This tests for leaks past the cap also.
 
While I never saw any coolant leakage, I found my 2.5 jeep engine low on coolant. I discovered it due to having a bit of low speed usage before shut down ..and I happened to be standing there when the rad started pushing air into the coolant recovery bottle. This was the only time coolant was visible on the ground. I freaked ..naturally ..and couldn't quite wrap around how the system held good pressure all the time hot. No cold start or shut down puddling that would have indicated a loose clamp. All clamps tweaked and all hoses showed no leakage when hot (good pressure). This happened a second time. I decided to replace the cap. So far it's worked. My only guess is that the cap held pressure, but not vacuum.

Again, I've only got half the mystery solved in terms of explaining it. The condition was corrected with the cap ..but I have no idea how the coolant got out without notice with the system holding good pressure and no apparent leaks.
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UOA shows no coolant.
 
Let us know what Pep Boys finds. My guess is cracked radiator, waterpump, ECTS, or radiator hose.
 
You need a sealed system to prevent boil off loss of coolant. The usual and cheap to check/replace suspect is the radiator cap.After a long highway ride is the water pump oulet hose to the radiator hot and stiff? If it is maybe not a pressure loss type situation. Are you the original owner? Is there one of the coolant flush valves in the heater core hose? If so check for leak and perhaps replace hose. You can get or rent a coolant system pressurized (like a small tire pump) and the pump up system and see if it will hold/get the pressure indicated on the cap. May also help to find a leak, follow the hissing noise.
 
If the engine is at operating temp, yes, you should definitely hear a hiss and likely have scolding hot coolant go blasting out of the radiator if you remove the cap!

If the cap is really old, I'd bet ya dollars to donuts it needs to be replaced. Bet that solves the coolant loss.
 
You should have pressure big time. Buy another cap or check for a hairline crack in the tank.

My Taurus had a tank crack.
 
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Originally Posted By: kingrob
Let us know what Pep Boys finds. My guess is cracked radiator, waterpump, ECTS, or radiator hose.

I took it to Pep Boys today and had them perform their inspection. They pressure tested the system and were unable to find any leaks. However, they suggested that I try replacing the radiator cap as it looked "questionable" and it may be the cause of my coolant evaporation.

So, I'll replace the radiator cap on Thursday in addition to replacing the hoses and thermostat. I'll also chemical flush the system and refill with new Dex-Cool. Hopefully this will resolve the problem.
 
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