Losing coolant out of overflow tank

[jamesr]

I recently rebuilt my 7mgte, but have been plagued with losing coolant from the overflow tank since day one. Runs fine until I really get on it. The car makes 402 whp, and compressioned tested at 180 multiple times.

Using arp bolts and a mhg torqued to 95 foot-pounds, and it has been retorque since break in.
It has always over pressurized the coolant system since day one.

Block was magnafluxed when built, the head was not tested just shaved and made smooth. Was recently rebuilt and gotten grind jobs, so I assumed it was ok.

I have changed the radiator caps a few times.

Car doesn't smoke white or at all for that matter, oil is clean, and radiator fluid is clean

I suspect I have a cracked head that only shows itself at high boost.

Is there any other possibilities or suggestions before I rebuild a new head?
Thanks for the help.

 

[hvyman]

perform a block test and a cylinder leak down test.

 

[jamesr]

perform a block test and a cylinder leak down test.

Ok I will try to take care of these test soon as I can. I will probably order my own tools, so once they arrive, I will do these tests and update, thanks for the advice.

 

[quickstudy]

same exact symptoms, same situation. Did you do those tests? After reading this, i'm going to do the same tests on mine.

 

[kdog1988]

What rad caps are you using? I was having same problem with cheap parts store caps changed to a Stant cap and no more problems. Also does it boil out or just over fills the tank?

Sent from my LG-E739 using Tapatalk 2

 

[grsupra87]

I know this sounds pretty goofy, but I had the same problem, and found that the nozzle-holes on the bottom of the overflow cap were plugged with debri's and the coolant was pushing out.

 

[quickstudy]

I block tested mine: negative. I do have a cheap radiator cap. I will be testing the thermostat, upgrading the radiator cap to a better brand, checking the overflow lines for clogs. If I don't find anything I will do static and dynamic compression, and do more testing on the dash guages.

 

[motorider9911]

Kdog brings up a good point, is the coolant boiling out or spilling out? Also is your gauge reading normal or does it fluctuate?

 

[gsxr141]

same problem here. fresh rebuild with about 8,000 miles on it. head and block decked, titan mhg, arp studs. recently lost some coolant out of the overflow, temp gauge goes to 3/4 after about ten min, then stays at half. I was thinking about doing a new thermostat and maybe a "good" rad cap.

 

[pmmfred]

im having the same issue lol

 

[gsxr141]

i just installed a new factory toyota thermostat and radiator cap. here's to hoping that works.

 

[gsxr141]

well,,,,,
the temp gauge never spiked this morning, and the rad was full.

BUT, the radiator shit the bed.
hopefully that was part of the problem the whole time.

 

[gsxr141]

ok, a little more info.....
the car loses coolant out of the overflow after i drive it hard. the upper hose seems to have a lot of pressure in it.
strangely, the temp gauge never goes past halfway. i did just replace it with a brand new one, so it should be ok.
is there any chance that it's NOT a bad headgasket? if so, what else could it be?

 

[suprajim54]

I have similar symptoms. My car has failed a block test, so I definitely have BHG. The car runs and boosts fine, but I lose coolant after a long or hard drive. I have no smoke, even at start up. If I drive it normally for short trips, I can go several days without having to add coolant. I see a few spots of oil in the coolant bottle, but no coolant in the oil. My car has an HKS headgasket and ARP bolts done by the previous owner. Retorque didn't help my case. I'm going to try a new Cometic gasket and a different head and ARP studs this time around.