Excessive cooling system pressure - causes ?

[cagranitz]

2000 Outback Wagon, EJ251 motor, Auto trans, 137K miles, complete new head gasket job and timing belt with water pump done at Subaru dealer at 100K miles.

 

A few weeks ago, I noticed a slight smell of coolant when the car was hot. I checked under the hood and noticed a small amount of coolant leaking from where the upper radiator hose connects to the block. I tightened the clamp and then checked it again in a few more days. It was still leaking a little so I tightened the clamp a little more. That seems to have stopped the leak there, but this morning I checked under the hood again and noticed droplets of coolant sprayed onto certain areas, such as onto the power steering fluid canister, plastic intake plumbing, etc. There also a few other wet spots. The top seam of the radiator housing looked a little wet where the metal crimp is. It almost seemed as if coolant may have been spraying out of somewhere. I drove it again today and then checked things when the car was hot. No collant is coming from the heads. The overflow canister is normal. The temperature gauge is normal. It almost seemed like there was too much pressure in the cooling system. I gave a slight squeeze to the upper radiator hose and surprisingly it seemed far too firm (excessive pressure). I realize that the system pressure normally increases when the engine is hot, but this felt too high based on the firmness of the hose.

 

I really think the system is being over pressurized for some reason.

 

Could this be a bad radiator cap ?

 

What else could it be ?

[Fairtax4me]

"Excessive" pressure is usually indicative of a compression leak into the cooling system. But it's hard to declare it "excessive" without getting an accurate actual pressure reading.

Did you have the hoses replaced when they did the HGs? If not then it's certainly time for some new rubber. Old hoses will tend to crack at the ends and it isn't visible until they're removed.

[djmark7]

try a new cap

[nipper]

New Cap

 

nipper

[valvestem]

Be interesting to know whether compression leak or radiator cap.

[cagranitz]

I will be installing a new Subaru radiator cap and thermostat tomorrow. I will post the results.

 

I truly hope it is not a compression leak since my understanding would be that means a head gasket leak. I would be very upset if that was the case since I just had the Subaru dealer install new head gaskets a mere 25K miles ago.

[edrach]

Replace the cap; use an OEM cap. Even if that doesn't resolve the issue, it's the first thing I would do as a start.

[cagranitz]

Ok, I changed just the radiator cap and drove it last night for a while. When I got home I checked for any additional leaks and didn't really notice any. The upper radiator host didn't seem as firmly pressurized as before.

 

BUT, my wife just arrived home and I took another look and noticed some sprays of coolant again.

 

I reached down to feel the LOWER radiator hose and it's COLD. That would tell me that the thermostat must be stuck closed.

 

Does that sound right ?

 

Looks like I'll be changing the thermostat tomorrow.

[cagranitz]

I also have a 2001 Outback Wagon, same EJ25 engine as our 2000 OBW, but with manual transmission.

 

I just got back from driving the 2001 and checked the lower radiator hose and it too was cold.

 

After thinking about what I said in my prior post, I realized it might be normal for the lower radiator hose to be cold, since the coolant just passed through the radiator, so it should be cold. I just expected it to be somewhat warm, but not actually cold.

 

So I guess that does not necessarily mean the thermostat is bad. Just as I would be suspicious that the head gaskets could be bad after only 25K miles, a new thermostat was installed along with a new water pump at the same time they did the head gaskets. So the thermostat has only been in there for 25K miles.

 

I am now backing off the idea of changing the thermostat.

 

Could it be a clogged radiator ?

 

Maybe I should try to get a kit to test for exhaust gases in the coolant ?

 

Any other thoughts/suggestions ?

[markjw]

I just went through alot of what your going through. My problem ended up being bad head gasket's. I replaced them both and now my car is running fine. The most troubling symptom I was having was bubbles in the coolant reservoir tank. I was having intermittent hot/cold air from the heater blower,I was having random temp gauge spikes, I was also finding the reservoir tank fill completely up with coolant after a drive. And,I was having the lower radiator hose ice cold compared to the upper hose after a 5 or 10 mile drive.

 

The one thing that was always constant was the bubbles in the reservoir tank. I tried 3 or 4 thermostates and a few diffrent radiator caps. I also changed the water pump out and burped the cooling system several times. Nothing would make the bubbles stop. Until now,now that I have replaced the HG'd,there are no bubbles and the lower radiator hose is luke warm at running temp.

 

From my research,I found that combustion gasses may collect on the engine side of the thermostat causing it not to open. Apparently,the top side/engine side of the thermostat needs to be immersed in hot coolant,void of air and gasses to function properly. Also,this collecting of gasses on the top of the thermostat was what was causing my heater blower to randomly go Ice cold.

 

I would suggest you go back to the dealer where you had your work done and have them do the hydrocarbon or whatever test they may perform to determine the problem.

[94Loyale]

You just had all that work done to the car. A lot of hoses and parts get disturbed in the process. Don't waste your money blindly replacing parts. You have a coolant leak somewhere. So find the leak. Is this Oley in PA? If so, you aren't far from me. PM and I'll pressurize the coolant system and we'll find the leak. That should be your first step.

[cagranitz]

I took the car to Penn Diagnostic in West Lawn and discussed the problem with the technician (Nick). He really seemed to think the problem was a bad/leaky radiator. He installed a new radiator and there hasn't been a single leak.

 

It would seem that I was misinterpreting the leaks around the radiator area and from the top radiator hose as excessive cooling system pressure.

 

He showed me the old radiator and the places where they typically develop leaks. Along the bottom edge where 2 smaller hoses connect to the radiator the metal edge seal is not crimped due to the connection for the hose. Over time this becomes a leaky spot. Overall I think the upper and lower seals in the radiator were simply dried out.

[CNY_Dave]

I took the car to Penn Diagnostic in West Lawn and discussed the problem with the technician (Nick). He really seemed to think the problem was a bad/leaky radiator. He installed a new radiator and there hasn't been a single leak.

 

It would seem that I was misinterpreting the leaks around the radiator area and from the top radiator hose as excessive cooling system pressure.

 

He showed me the old radiator and the places where they typically develop leaks. Along the bottom edge where 2 smaller hoses connect to the radiator the metal edge seal is not crimped due to the connection for the hose. Over time this becomes a leaky spot. Overall I think the upper and lower seals in the radiator were simply dried out.

 

 

Huh, I wonder if that's where my slight antifreeze smell comes from.

 

No wet spots, no drips, no coolant loss, just the occasional whiff.

 

 

Dave