Ej22 Overheating issues

[FlySwat]

I've done a search, and found a few good threads on this topic, but before I start replacing things I'd like a few final opinions.

I have a '90 Subaru Legacy FWD with the Ej22 motor, It has the (apparently common) problem of overheating when on the freeway but not while idling or at low engine speeds.

I bought this Subaru for $500, it had a cracked radiator. I replaced the radiator and put in a new thermostat, but the overheating problem remained.

The radiator has been burped, but I didn't use the bleed screw, so I'm going to try doing that in a few minutes. I've also heard that old radiator hoses can cause trouble, so I'll inspect those.

Basicly, you will be driving and the temp gauge will peg itself really quickly, then drop back down to normal after a few minutes. All my mechanical knowledge makes me thing its just a hot air bubble hitting the two coolant temperature sensors.

However, A friend of mine did a leakdown test on the engine, and when the engine was cold there was 0% leak, but once the engine had warmed up there was a slight amount of leak on one side. However, I do not think a small leak like this would cause the instant overheat issue, I think its more due to an airbubble in the coolant.

Any other suggestions? Waterpump is not weeping any coolant. Compression is good.

[vrg3]

Exactly how quickly does the gauge peg itself?

If it moves all the way from normal to the peg in less than a few seconds, that makes me suspect a short somewhere along the way between the temperature sensor lead and ground. The sender doesn't usually respond that quickly.

The temperature sensor used by the gauge is the one with a single spade connector on it. It is a thermistor which grounds through its body. The resistance of the sensor goes down as its temperature goes up. So, if the wire were shorted to ground, it would read as a very very high temperature.

You should definitely do a proper burp using the burp screw, but I'd also inspect the sensor and the wiring around it for a short. It's not cheap, but if you have to replace it it's part number 21203AA030 and lists for around 50 bucks.

Since the stock gauge is so useless anyway, maybe you could buy a cheap aftermarket water temperature gauge and use it at least while troubleshooting this problem.

[FlySwat]

Exactly how quickly does the gauge peg itself?

If it moves all the way from normal to the peg in less than a few seconds, that makes me suspect a short somewhere along the way between the temperature sensor lead and ground. The sender doesn't usually respond that quickly.

The guage pegs within one second. Is there a set impedance the sensor should be outputting that I could use my meter to test it with?

Also, if the temp sensor gets an unusually high resistance will the ECU store a trouble code on it? I just found a FAQ on checking codes and I'm about to pull them.

[vrg3]

The guage pegs within one second. Is there a set impedance the sensor should be outputting that I could use my meter to test it with?

I don't know what its resistance curve looks like... I'll look to see if any of the manuals I have mention how to test it.

You might want to try turning the ignition on without starting the car, and getting a buddy to jiggle the wires in the area to see if the needle on the gauge moves.

But you say this only happens on the freeway? Weird...

Also, if the temp sensor gets an unusually high resistance will the ECU store a trouble code on it? I just found a FAQ on checking codes and I'm about to pull them.

The sensor for the gauge is completely independent from the sensor for the ECU. If your problem is in fact the sender, then it's perfectly possible that the ECU is actually still seeing the correct readings. But, yes, if the ECU sees abnormal signals it should store a trouble code.

After pulling the codes, be sure to clear them to see which ones come back.

[FlySwat]

I checked the single spade connector (On the backside of the intake manifold, tapped into a coolant line, I'm assuming thats the right one).

While I cannot trace the wire as it quickly goes into a larger loom, I cleaned the connection and put it back on. We will see if theres any difference after I'm done burping the radiator.

[FlySwat]

Ok, I burped the radiator using the bleed screw for about 25 minutes. I then drove it around the block about 6 times before it started to slowly overheat.

At 3/4 gauge I drove it back to my shop and let it idle. It began to heat up idling (Which it hadn't done before) so I shut it off.

Looks to me like there was an air bubble in the coolant, but now that its out I have bigger problems.

Perhaps the 20% leak on one side is a cracked head? Sounds like I'm pulling the motor and pulling the heads.

[ciper]

I bet its the head gasket on one or both sides

The previous owner was a dumb ass. They drove with the cracked radiator until the coolant was too low. The engineoverheated with damaged the head gasket. Now exhaust gas is entering you cooling system displacing the coolant until the point that some parts of the engine are extremely hot.

I just donated a 90 AWD L Wagon with the exact same issue.

BTW, how exactly did you come to the conclusion that "the (apparently common) problem of overheating" ? Its far from common. In fact Ive driven one of my legacy nearly a gallon low on coolant and below the dip stick on oil on the highway without issue....

[FlySwat]

I bet its the head gasket on one or both sides

The previous owner was a dumb ass. They drove with the cracked radiator until the coolant was too low. The engineoverheated with damaged the head gasket. Now exhaust gas is entering you cooling system displacing the coolant until the point that some parts of the engine are extremely hot.

I agree, though I'm a little worried that the head with the 20% cylinder leak is cracked because only leaks cylinder pressure into the coolant when warm.

BTW, how exactly did you come to the conclusion that "the (apparently common) problem of overheating" ? Its far from common. In fact Ive driven one of my legacy nearly a gallon low on coolant and below the dip stick on oil on the highway without issue....

I was just going by the number of threads a simple "overheating ej22" search brought up.

[THAWA]

haha, the old blown headgasket on an ej22, i had one of those myself, pissed me off. good luck





only kidding. Does the coolant raise a lot while it starts to overheat? Like if you look in the overflow tank do you either see bubbles or is the coolant at a much higher level than cold, like way over the full line? Does it only overheat if you push it hard, or if you've been driving for at least 10-15 miles? If you constantly have to refill the coolant I'm going to agree with ciper and say its your hg's. Those were the symptomes of mine. It's not a very hard job to do, more time consuming than anything else.