cracked head or block? air entering cooling system under boost

[dirosa]

hey guys,

just need some direction on what further testing i should do to narrow down this issue. it's a jdm 2jz engine that was never opened up, with the stock twins on it.

when on the highway cruising, everything is fine, but once you start hammering it, the temp will rise, but the moment you let off the throttle, the temp will go down.

things me and my buddy have done/checked:

• bled cooling system 10+ times (always has bubbles after a drive)
• bypassed heater core (this was done before, but figured it might be relevant)
• changed thermostat
• pressure tested cooling system to 17 lbs, and compared with another car, and results are the same

so we were thinking about getting a leakdown test down to help narrow down if there is a particular cylinder that is leaking, but that doesn't necesarily help identify if you have to replace the block, or if you can just swap heads (i have a spare head, and wouldn't want to go through the hassle of doing all that for nothing if it's the block).

what do you guys think?

 

[mk3_7m]

Bubbling did you say? on the overflow tank or on the radiator??

 

[hvyman]

Get a combustion gas tester for the cooling system and do a compression check with all the plugs out and the engine hot.

 

[dirosa]

bubbling is from the rad
compression test hot is 180 across the board
combustion gas tester is weird.....if you hold it to the exhaust, it turns yellow to indicate combustion chamber gases, but if you use it on the rad, it turns kind of green, which according to the manual the color for diesels?

 

[hvyman]

On mine green means combustion gas in the cooling system. Yours might be different tho. I have a matco one.

Are you doing it with the engine hot? Its sometimes better to let the engine idle there with the rad cap off and let teh coolant to start smoking a tad. Just make sure the temp doesnt get too hot.

Radiator bubbling is not normal. The last bhg i had had 165-170psi in all cylinders and was only eating coolant(water actually since i had to refill so much) Never mixed with the oil.

Does it smoke at all? And if the cap is off and you rev it does the coolant shoot out of the radiator? Not just raise up but actually shoot out?

 

[chris_2jz]

I'm gonna keep my eye on this thread cause the same thing happens to my 1jz when I'm traveling long distance (high ways) my coolant gauge goes up 3/4th of the way but never reaches H. I have no thermostat in my car. Sorry to invade your thread just figured we can kill 2 birds 1 stone

Sent from my Galaxy S phone

 

[hvyman]

^ your problem is because you have no stat. Put it in. Your not gaining a thing by leaving it out. Back in the day old hot rod/muscle car guys used to think it was better to leave it out. They would go on long trips and it would over heat.

Also at 3/4 of the way up is like 230*+. Your overheating.

 

[chris_2jz]

^ your problem is because you have no stat. Put it in. Your not gaining a thing by leaving it out. Back in the day old hot rod/muscle car guys used to think it was better to leave it out. They would go on long trips and it would over heat.

Also at 3/4 of the way up is like 230*+. Your overheating.

Cool thanks man ill try and install one asap.



Sent from my Galaxy S phone

 

[Supracentral]

Do a compression test with the rad cap off. You'll find out which cylinder is leaking combustion into the water jacket that way. While it's uncommon on a 2J, you could have a blown headgasket. They aren't immune to it, just a hell of a lot more resistant to it than the 7m.

Regardless, you're going to have to tear it down to figure out what's wrong.

 

[dirosa]

finally bought a leakdown tester, and low and behold, cylinder 4 is leaking at 60% whereas all the rest are at 14%.

so, grabbing a jdm engine and swapping it this weekend. i'll rip apart the engine and find the crack if i have time.

 

[Suprapowaz!(2)]

What if it's just a HG failure to one of the waterjackets? Buying another JDM engine would be a waste. Why not tear it down and find out for sure first?

 

[hvyman]

Just find a new head if its cracked. Flush out the oil system real good so you dont get rk right after.

 

[dirosa]

out of time...........buddy is leaving to cali for 2 years in a couple of weeks, and needs this done so he can drive it down...........i actually have a spare head and block, but we don't have the time to magnaflux the head, find the crack, and replace whichever is faulty, and slap it all back together...........though i agree, it would be more fun to tear it down, but time wise, we don't have enough.