Ok, so, heres the thing. My engine is getting real hot after driving it hard(consistently above 3k rpm for an extended period of time). When it gets hot it blows all its coolant out the overflow and then it gets really hot, but if I drive the car nicely(constantly under 3k rpm) it stays in a the lower 1/3 of the temp range on the gauge. I have flushed the system, checked the fans, replaced the thermostat, cap, water pump and radiator and bled the system the way the 93.5 g20 manual recommends. A funny thing I have noticed is that the lower radiator hose is not getting hot, but the upper gets very hot. My current thoughts are that either; I got a faulty replacement thermostat, the cooling sytem is clogged internally, or the head gasket has a tiny opening between the cylinder and the cooling system.

Any thoughts?
-SR20DET_G20

sounds like the thermostat if ones only get hot....can u feel the fluid moving inside the tube? and how does the manual recommend it....removing that cap and letting ur car warm up and fill it as it sucks it in?correct?

If your cooling system is getting over pressurized before the overheating occurs, ie. the overheating is the result of the high pressure...it could be the result of a hole in the headgasket. What happens is some of the combustion gases escape into the cooling system and increase its pressure. I have seen this before on a DET with a replaced headgasket.

-saaby

Quick test: Run without the thermostat and see if it keeps happening.

Run the car with the radiator cap off in your driveway. See if lots of bubbles come out of the radiator. If so your head gasket it fuxked.

Take the thermostat out and see if the whole radiator gets hot.

Another way to check for a clog is to take upper and lower radiator hoses off and cram a garden hose in the upper one. Run the motor and make sure it spits out water at the other end.

I've gotten bad thermostats from auto store before. I've also sent radiators out to be flushed and got them back and they still caused the car to over heat. Stuff like this will really throw you for a loop.

Radiator is blocked, the top radiator hose is actually the outlet on the FWD SR20's. No flow means no heat to the bottom hose.

Radiator is blocked, the top radiator hose is actually the outlet on the FWD SR20's. No flow means no heat to the bottom hose.

Are you saying that the hot coolant leaves the engine into the lower hose and the "cooled" coolant re-enters the engine through the top?

I am going to test the thermostat and test the flow through the engine and hope I find something. Thanks for the responses, it verified what I was thinking.

A funny thing I have noticed is that the lower radiator hose is not getting hot, but the upper gets very hot.

Any thoughts?
-SR20DET_G20


http://forum.pulsar.org.au/showpost.php?p=1158937&postcount=45

Forget the red drawings.

The top hose is the engines outlet, the bottom hose is the inlet. So you have super hot water exiting the top of the motor via the head. It tries to get through the radiator but it is blocked. No hot water flowing means the bottom hose does not warm up. The engine keeps getting hotter, as there is no coolant from the radiaotr 'flowing' to cool it down.

Your radiator is blocked, pull the radiator out and have it flow tested(or just fit a Koyo)

I already have replaced the radiator with a brand new one. This is why I'm suspecting the thermostat or an internal clog.

try running with no thermostat and report back. It really sounds like the thermostat isn't opening to allow coolant through the engine.

fans are not turning on.. get new relay

fans are not turning on.. get new relay

Do you know if there is a highspeed and lowspeed relay on a 93.5 g20. I think my lowspeed fan is working, but when it is time for the highspeed fan there is no fan at all.

If your cooling system is getting over pressurized before the overheating occurs, ie. the overheating is the result of the high pressure...it could be the result of a hole in the headgasket. What happens is some of the combustion gases escape into the cooling system and increase its pressure. I have seen this before on a DET with a replaced headgasket.

-saaby


He is Right!!!;)

Is not the radiator or a cloged thermostat is your headgasket.... replace it:biggthump

Had the same probelm, changed my radiator cap and no more overheating also my man if your head gasket is gone it will push back the antifreezre back in the bottle and cause you to overheat, if it overheats too much then you just warped your head maybe the block depending on how bad you did it.

On more thind to check out if your fans are not coming on then check the fuse box inside the car that says Engine Control that for some reason or another triggers your fans if that fuse is blown then no fans.

I just checked my thermostat, and it's FINE. I ran the hose through the engine and it seems to flow perfectly fine... so *sigh* I'm thinking that the thermostat, for whatever reason, is not getting hot enough to open. I'm kind of thinking faulty water pump, but I was told it was replaced right before I bought the car. Does anyone know a good way to test the water pump? Thanks.

I have the thermostat out now, do you guys think I should still test the car without it?

yes, without the T-stat the car will run ice cold. if that fixes the problem then the problem might bewith the thermostat. keep in mind though wih the t-stat removed the car is going to take a verrrry long time warming up. and it also may not be the problem.

Dude, your head gasket has a leak. It pressurizes the system and creates an air pocket. The t-stat does not kick over because there is a big pocket of air around it and not hot water.

My scoobaru does the same thing. If I let it get hot, and then "bleed" some air out of the system, the t-stat will kick over, and all is good. I've been driving like that for 5 months now, but then, my scooby only has about 30 HP to begin with anyway.

Dude, your head gasket has a leak. It pressurizes the system and creates an air pocket. The t-stat does not kick over because there is a big pocket of air around it and not hot water.

My scoobaru does the same thing. If I let it get hot, and then "bleed" some air out of the system, the t-stat will kick over, and all is good. I've been driving like that for 5 months now, but then, my scooby only has about 30 HP to begin with anyway.


Dude.... dude... that sucks. I really don't want to do a head gasket on this thing. With the TMIC and the turbo it would probably take me a week. I really hope your wrong, but what you are saying makes total sense. Would I go to hell if I just pulled out the thermostat to sell the car? Better yet I could stick it open somehow. I wonder if I drilled a small hole in it if that would prevent the air bubble from forming.

Its weird to me that any of you say dude THIS IS your problem. even with the best description no one can be 100% sure unless they test the stuff themselves. He could be leaving out info and not meaning to. a new thermo is what 6 bucks if you feel it could be a faulty thermo then go grab one real quick or run without. Being in this heat I bet it don't take all that long to warm up. lol then again I don't know the weather in Oregon. It's sad cause it could very well be the head gasket.. for that I'd go to harbor freight buy a compression tool and do a compression check on the motor.