acw

OVERHEATING - - -Radiator Cap?

Hey Friends,

2003, 3.5 Motor : The Car appears to be losing radiator coolant...and i don't know where from?

Every month (of therebout), the car starts to overheat. I'll be driving along and happen to look at the heating gauge and see it run at 3/4 and higher. I stop the car, open the hood and see the overflow tank at "3/4" full. Both Fans are Turning. I get back in the car and turn on the heater, roll down the windows and drive home (torture down here in Fla. with no AC).

When i get home, I let the car cool down. Again, I check the overflow tank and its 3/4 Full. I then open the radiator cap and see the water is DOWN. I turn the car on, and then pour about 1/3 to 1/2 gallon of anti-freeze/coolant STRAIGHT into the radiator. The car then runs at normal temperature for about 1 month.

1. Why is the overflow tank full, and the Radiator Low?
2. Again, i do this routine about once a mth...?
3. I suspect its the radiator Cap....which one should i buy (they are cheap at Autozone) ?

Thanks for your constructive input...!

~T

Cotozic

You can find out if it's the cap if you can see dried antifreeze in your engine bay. This could also be a leak elsewhere... but it will help you find the source. It kinda looks like salt residue, which i initially confused it with here in the winter. Also, keep in mind that the fluid levels in the reserve tank changes when your car is hot. These radiators are known for leaking from the cap or microfractures in the plastic top panel because of the way people might slam the hood down. Check to see if any gunk is building up on the crevices where where the plastic top of the radiator meets the metal grating.

I had a leak there that got really bad. It started gradually, then it became a daily fill up game. I didn't even know i had a problem until it was bad.

mclasser

Check for leaks at the upper and lower hoses, t-stat and the radiator itself. The rads on these cars love to leak at the top where the plastic tank meets the aluminum core (see pic below). My rad's been leaking here for the past 2 months (will replace it soon) and I have to top off the coolant every few days. You may have to remove the air vent near the battery to get a better look. Could be the cap is bad as well. Inspect its seals for cracking/grime. Only buy an OEM cap. You may also have air in the cooling system as a result of the bad cap and/or leak.

When was the last time the coolant was changed?

DennisMik

iTrader: (2)

The radiator cap is a very mis-understood piece of the car. The main purpose of the radiator cap is to cause the cooling system to run pressurized at about 15psi. What this does is raise the boiling point of water to approximately 250º F. The chemicals in antifreeze also raise the boiling point to something above 212º F, but I don't have a number.

When you have a leak, you can remove the radiator cap and drive the car without the cooling system pressurized. Without any pressure, the leak will be much less. If your radiator isn't plugged and the cooling fans are working, you can drive in all but the most extreme of conditions.

Then there is the overflow tank. What this does is collect and hold the excess coolant from the engine one it has heated up and expanded. When the engine is turned off and cools down, the coolant in the engine contracts and creates a vacuum. This then sucks the previously excess coolant out of the overflow tank. The radiator cap plays a part in this. It has to open up under the vacuum to allow the coolant to flow.

But if you have a leak in the cooling system, the vacuum created by the cooling coolant will not suck anything out of the overflow tank. Air gets sucked in through the leak instead.

In the original post it is stated that the radiator level is down, but the overflow tank seems to always be the same. This says there is a leak somewhere.

The radiator cap is fine.

chrome91

iTrader: (1)

if you radiator cap is bad and venting coolant to the reservoir at too low of a pressure, it can flood the reservoir and have no coolant to suck back in causing air in the radiator

other thing is if the headgasket is bad, combustion gas is getting into the radiator, pushing coolant out of the radiator to the reservoir, and the combustion gas stays in the radiator

DennisMik

iTrader: (2)

The coolant that goes into the overflow tank when the engine is hot is determined by the physical volume of the hot, expanded liquid. Theoretically the pressure plays no part, but in reality it does. There will be less coolant transferred to the overflow tank in a pressurized system versus a non-pressurized system. This is caused by the pressure stretching/swelling the rubber hoses, which increases the capacity of the cooling system by a tiny amount. There isn't really any noteworthy difference in the amount of coolant that goes into the overflow reservoir in a pressurized system versus a non-pressurized system.

The overflow tank can hold a lot more than the normal expansion amount. Picture the markings on the expansion tank. Level hot and level cold. This is your normal expansion amount. Unless the coolant is actually boiling or you have combustion gasses from a bad head gasket, you won't overflow the tank. You can't blame the radiator cap if this happens.

chrome91

iTrader: (1)

yes, but if the spring on the cap is weak and venting at 10lbs instead of the normal 16 would it not allow excess coolant into the reservoir as in enough to flood it?

acw

Ok...So Dennis, you are saying that it could NOT be the Radiator Cap ---THEREFORE a leak must be from another part of the system...Now where might that be ?

YOUR LOGIC makes sense...

ALSO, could the leak be coming from the Radiator Cap ?

PS. Just checked the Overflow tank this morning. The car was completely cold. The Overflow tank is now 1/3 Full, which means some of it went back into the system----The Tank Level Now Shows its on its Max Fluid Level "Line."

Thanks ALL for the Comments !

~T

DennisMik

iTrader: (2)

The amount of coolant that goes into the expansion tank is controlled by the physical expansion on the liquid. As the liquid heats up and expands, it creates pressure in the system. A weak spring in the thermostat would allow the liquid to escape sooner, but the amount will still be pretty much the same because the expansion will be the same. It may be a tiny amount more, but not significantly more.

DennisMik

iTrader: (2)

A leak could be anywhere there is a hose or something that the coolant flows through. The most common point for these cars to leak is the radiator, on the top corner in the area where the upper radiator hose attaches. The photo posted by mclasser is an example of this.

Your leak is still small, a half gallon in a month is not major yet. Similarly it is not severe enough to drip on the ground yet. It gets evaporated by the engine heat. If the radiator were to be leaking, the coolant would probably be splashing on the engine and drying. Does the engine look like it got mud splashed on it? That's kind of what dried, baked antifreeze looks like.

Could the radiator cap itself leak? Absolutely. It's made by made man and anything made by man is guaranteed to fail somewhere along the line.

But a leak should be leaving some sort of residue. a small leak just means that you have to look harder for it.

acw

Thanks again Dennis...always look forward to your input!

~T

acw

Hey Buds,

Solved this problem by changing the Top Radiator Hose. It looked SWOLLEN and from some detective work, my mechanic could see that RADIATOR fluid was coming out of the Hose at the connection towards the motor (green residue). YOU HAD to have the Car on a Lift to see this...not visible from Above.

Thanks for your Help!

~T