Subie Cooling Problem Solved?

[ArdWrknTrk]

Well, it ain't fixed. Yesterday we drove it 275 miles, most of which was running 65 - 75 MPH with a very strong crosswind. The temp never wavered, sitting exactly where it always does.

But the expansion tank, which started just a bit higher than the Full mark, was almost completely full when the trip was over. Not so full that we'd lost any, but still very full.

And this morning it hadn't sucked any back into the radiator. Granted it was still warm in the garage, with the outside temp 79 degrees and in the garage it may be in the 80's. But it hadn't pulled any back. And when I pulled the radiator cap it spit a bit of coolant out of the expansion tank. I don't know if there was still pressure in the system, but it didn't feel like it.

I'm thinking the cap isn't opening up and allowing the vacuum to suck coolant back in. So, I want to put a Subaru cap on it and do more testing, and think we'll drive down to BA to the Subie dealer tomorrow to get one. (Should have purchased the one David found. )

And I'm also going to pull the hose from the radiator's neck to the expansion tank and make sure it doesn't have any leaks.

Then I'm going to pull the fan connectors and let it idle until the temp comes up, at which point it should push coolant into the tank. And I'll shut it off and see what happens.

Anybody with better ideas?

If the radiator is full it will always be pushing into the expansion tank (once the hoses balloon)

Just like ice, water is powerful stuff as it heats up, and it is going to go somewhere

[Gary Lewis]

If the radiator is full it will always be pushing into the expansion tank (once the hoses balloon)

Just like ice, water is powerful stuff as it heats up, and it is going to go somewhere

Yes, but when the system cools it should pull the coolant back into the radiator. And this one didn't.

[Gary Lewis]

Yes, but when the system cools it should pull the coolant back into the radiator. And this one didn't.

Inspecting the Stant cap closely I find that the "vacuum valve", as shown in the drawing below, has a stronger spring on it than I remember from other caps. This leads me to believe that it isn't releasing as the system cools, so coolant isn't sucked back into the radiator.

For those that might not know, here are three snippets from this site on how the radiator cap is supposed to work:

 

[ArdWrknTrk]

Inspecting the Stant cap closely I find that the "vacuum valve", as shown in the drawing below, has a stronger spring on it than I remember from other caps. This leads me to believe that it isn't releasing as the system cools, so coolant isn't sucked back into the radiator.

For those that might not know, here are three snippets from this site on how the radiator cap is supposed to work:

I understand the principal.

I was the one that suggested OEM in the first place.

[Gary Lewis]

I understand the principal.

I was the one that suggested OEM in the first place.

I knew you did, Jim. And I expect most people do. Was just explaining in case someone didn't.

And I do remember you recommending OEM. But this car's been running an aftermarket radiator cap for years, so I didn't expect there to be a problem. However, I am sure hoping that's the issue. We shall see.

Also, there's an exhaust doughnut that has given up the ghost, so I'll get one of those while I'm at Subaru tomorrow. And I'll be squirting the studs for the exhaust with penetrating oil today.

[Gary Lewis]

I knew you did, Jim. And I expect most people do. Was just explaining in case someone didn't.

And I do remember you recommending OEM. But this car's been running an aftermarket radiator cap for years, so I didn't expect there to be a problem. However, I am sure hoping that's the issue. We shall see.

Also, there's an exhaust doughnut that has given up the ghost, so I'll get one of those while I'm at Subaru tomorrow. And I'll be squirting the studs for the exhaust with penetrating oil today.

Time for an update and a plea for help.

Let me try to summarize - the Subie pushes coolant out to the overflow tank, as it should, but doesn't pull it back when the engine "cools". In fact, having sat outside overnight where the temp got down to 80 degrees, and then running cold water from the hose over the engine and radiator for 20 minutes there was still a slight pressure in the system when I pulled the cap. However, the system was down 1 pint from a 75 mile trip where I ran it at 65 - 75 MPH, and frequently into a significant head wind.

Obviously with pressure in the system it isn't going to pull a vacuum and suck the coolant back. But, what would cause the system to still be under a slight pressure?

I'm at my wit's end and need help - in more ways than one!

[ArdWrknTrk]

Time for an update and a plea for help.

Let me try to summarize - the Subie pushes coolant out to the overflow tank, as it should, but doesn't pull it back when the engine "cools". In fact, having sat outside overnight where the temp got down to 80 degrees, and then running cold water from the hose over the engine and radiator for 20 minutes there was still a slight pressure in the system when I pulled the cap. However, the system was down 1 pint from a 75 mile trip where I ran it at 65 - 75 MPH, and frequently into a significant head wind.

Obviously with pressure in the system it isn't going to pull a vacuum and suck the coolant back. But, what would cause the system to still be under a slight pressure?

I'm at my wit's end and need help - in more ways than one!

I do a reagent test for combustion by-products.

Cracks and gaskets can open up under load and close when there is none, or the heads start to cool.

If you don't have any oil in the catch bottle there are few other things it could be.

[Gary Lewis]

I do a reagent test for combustion by-products.

Cracks and gaskets can open up under load and close when there is none, or the heads start to cool.

If you don't have any oil in the catch bottle there are few other things it could be.

According to the mechanic there are no products of combustion in the coolant. And there's no oil in the overflow tank nor radiator. Nor coolant in the oil. Plus, if you carefully put what is in the expansion tank above the Full mark back in the radiator the radiator is full each time, so we aren't losing coolant.

The issue really is why the system is staying pressurized. Not high pressure, but even after sitting overnight and then having cold water run over it for 20 minutes there was still a bit of pressure. So it won't suck any coolant back.

And, on each drive it seems to push more coolant into the overflow, so it isn't long before it is low.

[ArdWrknTrk]

According to the mechanic there are no products of combustion in the coolant. And there's no oil in the overflow tank nor radiator. Nor coolant in the oil. Plus, if you carefully put what is in the expansion tank above the Full mark back in the radiator the radiator is full each time, so we aren't losing coolant.

The issue really is why the system is staying pressurized. Not high pressure, but even after sitting overnight and then having cold water run over it for 20 minutes there was still a bit of pressure. So it won't suck any coolant back.

And, on each drive it seems to push more coolant into the overflow, so it isn't long before it is low.

 

I'd think the system would have to develop negative pressure (if the overflow is at atmospheric) to suck coolant in.

Hydraulics behave a certain way.

For a full system to have positive pressure after discharging some fluid and cooling back down, defies physics

[1986F150Six]

Well, it ain't fixed.

And I'm also going to pull the hose from the radiator's neck to the expansion tank and make sure it doesn't have any leaks.

Anybody with better ideas?

I don't know about it being a better idea, but here goes. If you did not find any leaks in the hose going to the expansion tank [I assume not as you did not report doing so], then maybe there is a blockage inside the tube? Perhaps under higher pressures [16+ psi], hot coolant can get by the blockage, but at lower pressures, the blockage is such that what is in the reservoir cannot be drawn back and a few psi is maintained above the cap, preventing the cap from being able to operate as designed?