BHG symptoms...but no BHG?

[RNEMESiS42]

My birdcage light has been coming on and off every once and a while ever since I bought my car four years ago. Around last April I was driving my car when all of a sudden I saw steam coming up from the hood. I pull over and see that my radiator overflow tank is filling up. The temperature gauge in my car looked normal. I drove home and parked my car indefinitely, fearing a blown head gasket. I haven't driven my car since then and recently decided to test it for a BHG. I purchased the $45 block test kit form NAPA, and tried it out. I did it twice, and got negative results for exhaust gases in the coolant. Afterward I drove it about a half mile and back, and noticed when I parked that the same issue is occurring: coolant spilling out into the overflow tank.
What could be wrong? Thermostat or radiator busted? I have no other signs that would relate to a BHG.

[btwilson86]

Have you ever messed with the line going in and the line going out of the cap on your overflow? If so, you might have them backwards....

Basically what would happen is this: as your car heats up, pressure forces coolant into overflow through the tube that feeds to the bottom of the reservoir. As the car cools down, it'll suck the coolant back into the cooling system via that same hose.

If the lines are backwards, as the coolant expands it'll fill up the reservoir as it normally should. The problem is, it can't drink it back up cuz the line running from the radiator is not hooked up to that little hose that goes to the bottom of the reservoir. So the coolant will just sit in there.

Next time you drive the car, more coolant will try to go into the reservoir. Once it's full it's gonna go straight out that other line on the overflow cap, which is the purge line that goes straight to the ground, thus making it seem like an over-pressurized cooling system (like with a blown head gasket) when in reality it's just 2 hoses hooked up backwards.

That was alot longer than I thought it'll be, sorry for the ramble

[RNEMESiS42]

Thanks for the response, I'll check it out in the morning. I've never directly messed with my overflow tank, but it sure would be nice if it's as simple as this.

[RNEMESiS42]

There's just the one line from the top of my radiator to the cap of the overflow. It all looks fine to me.

[Bill UK]

1. Thermostat not opening. (stuck closed)
2. Water pump impellor vanes corrode.
3. Blocked rad
4. Viscous fan coupling slipping
5. Also check this out Link

[oregonjoe]

I too had the same problems, blowing coolant out reservoir, no hot temp on gauge, negative test for exhaust gas – but in the end, it still was a BHG, The best test for BHG in No 6 cylinder is to look at spark plug – you will see a difference in the plug for the BHG cylinder compared to the rest (looks like the coolant color). The EG test does not find minor leaks when the compression is high.

Looks at the plugs and if it looks like a BHG, Runs like a BHG and smells like a BHG – then it probably is!

I had to pull and rebuild my engine as a result.

[RNEMESiS42]

Phew...I just found the part number in this thread:

I'm going to to buy that sucker and the gasket, and be on my way...this has been l the fun replacement of a thermostat ever.

[ddmcse]

when dealing with a possible BHG on a supra don't use Napa parts . you might save 7 dollars but you've got no piece of mind now.
wouldn't you feel better knowing it was a yota thermostat ?