This car has about 180,000 miles on it, has a carb, manual transmission. Right now it is pushing coolant into the coolant recovery tank, and not sucking it back up. Every day the radiator is a little low on coolant (more or less depending on drive time) and needs to be topped up with the excess coolant in the recovery tank.

 

I am guessing I have a blown head gasket. Whatever the problem is, I would like to diagnose and repair it myself. Any suggestions are welcome.

 

Thanks....

Make sure that you are not over filling the radiator. There needs to be an air pocket for expansion of the coolant. To full with coolant, and it will dump it out as the coolant gets heated.

 

Also, that air pocket is needed for the pressurization of the system. System pressure is key to raising the boiling point of the coolant. Low or no pressure and she'll run hot, boiling over into the recovery tank.

 

Run the engine with the radiator cap off, see if it wants to push the coolant out as it heats up. Also check for bubbles in the return tank of the radiator as it runs. Those are 2 signs of a blown headgasket.

Sounds more like a bad radiator cap. If it has a factory overflow tank, then fill the radiator all the way. If it's not drawing back in from the tank, make sure the cap vacuum break is working (little metal circle on the underside, it should move easily with finger pressure), and also make sure the hose for the overflow goes all the way to the bottom of it. If it's just at the top of the tank, it'll only suck air back in.

When I start the engine with the radiator cap off (cap is new) coolant is slowly pushed out the top of the radiator and bubbles emerge intermittantly.

 

The overflow tank is original, with the hose connected to the bottom of it. I've checked out the tank and hose to make sure nothing is plugged and there are no leaks.

 

I will run the car some more with the cap on to see if bubbles come out in the overflow tank and if they do, I'll see if I can smell exhaust gas in the tank.

 

Thanks for the replies.

sounds more like a bad radiator cap...

+1

Replacing the radiator cap was one of the first things I did and it didn't seem to change anything.

Could it Be a Stuck Thermostat? ...

if your Subie`s Engine Never had operated at Overheating Temps, I believe it is not the Heads Gaskets, just the Thermostat got Stuck.

I Suggest to Check it Too and Replace if Needed.

Kind Regards.

Good idea to check the thermostat. I'll do that. The car did overheat at least once when it was low on coolant.

 

Thanks for the suggestion.

Sounds more like a clogged ratiator to me. I recently rebuilt my engine only to find out that the problem still exsisted. I used a laser temperture measuring device and found cold spots in the radiator, once I replaced the radiator, the problem went away. The problem was identical to what you are saying.

Thanks Dr. Rx. I didn't tell you that the car has a new radiator. I replaced the thermostat today and if that doesn't fix it I'm going to get the raidiator coolant analysed for exhaust gas on Thursday. I appreciate the fact that I need to get a good diagnosis before proceeding with expensive repairs.

Thanks Dr. Rx. I didn't tell you that the car has a new radiator. I replaced the thermostat today and if that doesn't fix it I'm going to get the raidiator coolant analysed for exhaust gas on Thursday. I appreciate the fact that I need to get a good diagnosis before proceeding with expensive repairs.

 

Thanks for the update. An analysis, is a great start, but not always accurate. On my hrydrocarbon test, the test fluid turned a blue green, showing that there was a present of hydrocarbons in the water. The test fluid in suppose to go from blue to bright green. It was based upon that test that I decided to rebuild the engine only to find out that the problem was the radiator. I have no idea where the small amount of hydrocarbons came from, maybe from using spray lubricant on the hoses to make them easier to install. Anyway, good luck on your journey, let us know what happens.

I changed the thermostat, and had the radiator checked for exhaust gases at the Subaru dealer. The dealer told me that I don't have a blown head gasket.

 

For now everything seems to be working properly, haven't had to add any coolant for a few days, but the car hasn't been driven for more than 20 miles at a time. Later in the week the car goes our 80 miles or so, so I'll see what happens then.

 

I have the impression that it can be really difficult to get all of the air out of the system. I noticed, when looking at pressure testing equipment there are special tools to make sure you get all of the air out of the cooling system when refilling it. Funny, I never had these kinds of problems before, and I pulled the engine our of our 81 subaru a couple of times.

Overheating problem can be a real bear to solve, sometimes they seem to solve themself. I've have a reoccuring one in my JDM powered Impreza. Once it was the radiator, but I didn't find that out until I have rebuilt the engine.

I replaced the thermostat and had the radiator checked for exhaust gas at the local subu dealer. The dealer said I don't have a blown head gasket. The coolant level has been good in the car for a few days now. I'm waiting for it to be driven more than a half hour at a time before I'm fully satisfied it's ok, however, it doesn't seem to be losing coolant anymore.