IrocZ'85

iTrader: (9)

Hey guys,

I finished my swap about 2 months ago and have since gone WOT around the neighborhood a few times and also made about 4 WOT dyno pulls a few weeks ago. Last week i was driving about 30 miles south on the highway....no spirited driving..just cruising...and the car overheated and just turned off. First I was wondering if anyone knows whether or not the engine is commanded to turn off by the PCM from high temps or whether it is mechanically seizing? If mechanical, i hope i didn't impart enough heat to warp the aluminum heads/block.

Anywho, i've confirmed that the thermostat is good and even replaced it, confirmed that the water pump is moving water, that the system is pressurized and my thirdgen radiator is fine. Overflow tank is mounted properly in elevation to evacuate air, vent lines are clear and flowing and plumbed properly (shouldn't be any airlocking to cause localized boiling in the tubes).

I tried to think of anything on engine that I changed from the day previous when it wasn't having heat issues....nothing different. Secondly, there has always been a faint but definitively sweet smell from the exhaust, but never plumes of white smoke. On top of this, when the car was overheating on the side of the highway you can physically feel the upper radiator hose swelling from pressure and hissing from steam, besides being excruciatingly hot. The overheat condition doesn't happen rapidly...infact I can drive the car about 10-15 minutes before it slowly creeps up and pressurizes the upper hose. So this led me to believe it was potentially a hairline fracture in the headgasket, or maybe i was somehow lifting the head. Today I tore apart both heads and don't see any noticeable gasket wear or fatigue. I guess I'll just go ahead and replace them and see what happens. Anyone have any ideas or last ditch efforts I should test? thanks!

86White_T/A305

That does sound quite odd,have you checked the oil after the car has sat and cooled off for any signs off coolant?

I had my lq4 over heat once because my power steering pulley broke off the pump itself(was crazy) and yes the pcm shut the motor off within ten mins limping the car a few blocks over to the garage.

Sounds like something isnt functioning 100% or blockage in the system.Are you running the heater core or was it bypassed?How well was the coolant burped when you added coolant during initial startup after the swap?Have you checked that the fans are infact coming on when the ecm commands it? Trying to toss out ideas...but i will say after my swap I burped my car 3 times and by the 3rd time I got a pretty good airpocket out and now it runs perfectly 160* with the stock t-stat and fan 1 comes on at 155*

I wouldnt be surprised if the water pump gasket is partially blocking the part..the original gasket on my ls1 had done this and the new replacement gasket were thicker orange ones and much better quality.

techrunner

definitely check on burping all the air out of the cooling system. i had to do it several times before it quit taking more coolant, but eventually i got it all and now it doesnt get hot if i'm moving at all. fans arent needed unless i am parked. before i got all the air out, i could just watch it get hotter on idle until i finally shut it off for fear of overheating.

IrocZ'85

iTrader: (9)

thanks for the replies! Ok well I'll just go ahead and replace the head gasket, water pump, make sure the new thermostat is good and then meticulously bleed the system!

IrocZ'85

iTrader: (9)

If anyone else is interested in the PCM values for these engines regarding the built in over-heat protection, I've got a screenshot from the stock calibration. I believe this is for a 5.3 LM7, but last time i checked it was the same as the LS1 cal i have.


As you can see, once above 129C for 10 sec, it will engage protection mode and separates the cylinders into 2 groups and modulates how often they are fired. This severely hampers torque production which I can attest to, and it acts an awful lot like the active power management setup since cylinders are periodically "turned off" to promote cooling via airflow. But if you're still unlucky enough to reach 139C(~282*C) and sustain for about 6 minutes, the PCM will command the engine to shutdown. This happened to me as well lol.

I've got access to alot of the raw PCM calibration data in-case anyone is interested and have cals for lq4/9, lm7, LS1/2/3/6/7, duramax, and numerous L32 and L67.

IrocZ'85

iTrader: (9)

Looks like I may have found the culprit to the overheating issue. Remove my water pump today and immediately found this little piece come out of the thermostat port:


I want to remove the entire impeller to see the damage inside the pump..but I'd bet money this is what's causing my problems lol. I've got a replacement pump coming tomorrow....but does anyone have any ideas about how I could make sure more metal hasn't been sent through the block's water jacketing or even through my radiator? Last thing I need is to install a new pump and send metal back through it lol

88blackiroc

iTrader: (1)

Definitely get some pics of inside the pump. I hope that was the only piece that broke off for ya.

IrocZ'85

iTrader: (9)

I'll upload pics of the pump in a bit, i had to torch the impeller off and the pulley as well. The impeller was intact and nothing was broken....neither was any interior piece of the water pump casting from what i could see....so i feared that a part of the block or heads had somehow come loose. I looked into the water jacketing cavities of both...and nothing looked amiss...so im really stumped as to what happened hear. I'll take the pump to work and boroscope it just to see if something inside truely came loose.