Empty pressure bottle when cold, half full when hot

[Zapa89]

I've been slowly working on my '89 Cherokee and one of the latest "magic tricks" he's doing is this: When the engine is cold, the pressure bottle is empty, and when the thermostat opens, it fills up to the proper level.

I tried to fill it to half when cold, but it quickly fills up when hot, and since I didn't feel safe seeing the bottle full and pressurized I turned off the engine, let it cool a bit and relieved the coolant level.

I guess there's a giant air bubble trapped somewhere, but what's causing the system not to take the coolant when cold, yet keep the bottle half full?

Thanks.

 

[Johnnie Walker]

Park with engine facing downhill, or jack up the rear of the vehicle a good amount. Remove the CTS from the driver rear of the head, and fill till fluid comes out. If totally cold you can even run it a bit, while the sensor is out, and install it before it gets too hot and fluid goes EVERYWHERE.

 

[Zapa89]

I'm going to take the radiator out to be cleaned and maintained, so the refill will be properly done. I don't think it's been done in the 27 years this Jeep has, so that won't hurt.

I understand that after the CTS is back in place I have to run the engine up to temp and turn on the heater, so the heater core is included in the circuit, and refill at the pressure bottle as it goes. What baffles me is how the pressure bottle can be empty when cold and start filling up when the engine gets to temperature... I mean, where is that coolant coming from and why doesn't it stay in the lower areas of the circuit so I can properly fill from the pressure bottle?

 

[8Mud]

I fill my surge tank (pressure bottle) half full when cold. A pint (500 ml.) or more of expansion as the coolant heats is normal. A little spewing or discharge of coolant out of the cap can happen until the system finds the proper level.

Make sure the cap seals, the pressure relief in the cap is free and functioning.

Wild swings in fluid level and spewing can be a sign of a partially clogged radiator. Reduced coolant flow can cause hot spots and create steam in the system.

Use distilled water, check the surge tank for hairline cracks (common) reduced pressure lowers the boiling point of coolant. Any pressure leaks can cause issues.

Makes sure the cap seals well. Look for deposits on the inside of the cap possibly jamming the purge valve (pressure relief).

The proper coolant mix also raises the boiling point of coolant.

Does your temperature gauge remain mostly stable after you reach operating temperature. Some minor temperature variations are normal.

Like mentioned air in the system is by far the most common cause if large fluctuations in the coolant level.

 

[DieselSJ]

Scrap the stock cap and get a Stant 10224. Do NOT get an imitation. Find a Stant. They are less than $10. Application is mid-80's Volvo. They fit better and have a higher pressure rating.

 

[Zapa89]

I don't think my tank is the original one, but it doesn't appear to be cracked. The cap is certainly keeping seal.

 

[8Mud]

Doesn't look right to me. Maybe it is just hard to make out in the photo but I see no return line from the surge tank?

Check out the photo here. http://goo.gl/TqctlZ

 

[Zapa89]

It's the one that can be guessed in the shadows, going down. Same placement as in any other tank.

 

[Zapa89]

I finally managed to get the level normally stable.
I filled the tank up to 2/3 or so and started the engine with the tank's cap open and heat on full blast.
When it reached temperature the level fluctuated, sometimes up, sometimes down, gurgling coolant out sometimes (due to huge bubbles trapped getting out).
If the level would go very low -but before it could leave the return line empty and take air in- I would refill.
I kept checking the temp and watching spewing or refilling until the circuit simply kept its level and cooland circulating normally.
Then I closed the cap and kept it running for 10 minutes more.
Next morning the level was lower, but there was still coolant at the tank, so I made a last refill and it's been nice the whole weekend. 98ºC (210F) and with the electric fan switching on when it should.

Tomorrow I'll take it to clean the radiator anyway but at least I know everything is working properly even when it's probably partially clogged, so it can only get better

Thanks for your suggestions and help

 

[cruiser54]

Get the suggested cap.............

 

[Zapa89]

Get the suggested cap.............

The cap is fine. (.............)

They broke the radiator at the lower hose's tube when taking it off, so I'm getting a new one instead.

 

[DieselSJ]

The cap is fine. (.............)

They broke the radiator at the lower hose's tube when taking it off, so I'm getting a new one instead.

Good time to switch to open system.

 

[cruiser54]

Good time to switch to open system.

Yup.

 

[Zapa89]

Good time to switch to open system.

I don't really need the extra expense, and the closed system is as good as any

 

[cruiser54]

I don't really need the extra expense, and the closed system is as good as any

Radiator is the same price open or closed. All you need is a $12 recovery tank and some hose.

The failure rate of the bottles is very high and can strand/cause catastrophic damage without warning.

Obviously our choice.

 

[DieselSJ]

I don't really need the extra expense, and the closed system is as good as any

Closed to open using your existing radiator so you don't have to screw with the fan switch.

1 - Buy one of these. -

2 - Splice it into your upper hose.

3 - Remove pressure bottle and install later year heater control valve in its place (this also gives better HVAC operation).

4 - Add cheapie overflow bottle from your local parts house.

Drive and never worry about the plastic bottle again.

 

[cruiser54]

63745 Moroso inline filler.
11038 Napa heater hose
11039 Napa heater hose.
Universal recovery bottle.

No more heater control valve and cleaner engine bay.

 

[DieselSJ]

*Deleted*