Good day. l just completed a factory head/cam/lifter rebuild on an 03 Z06. lt has l believe 150xxx or so miles on it. Very similar to the build l just did on my own car few months back with exceptions that this was a complete stock rebuild whereas mine was a ported head/stage 2 BTR cam/ intake manifold etc. Both builds received brand new radiators/condenser/water pump/belts/upper lower rad hoses/and 160therm. Now my modified car goes down the freeway (cruising 75-80) at about 170. The other at around 220. Does anyone have any ideas what could be causing this? There does not appear 2b any air pockets in the block, no radiator blockage, no smoke coming from exhaust or low coolant issues, and the car runs great. Pulls hard and runs smooth. This is at least my 5th or 6th build of similar nature and l have never had this issue before. Any suggestions at all, no matter how obvious or not, would be greatly appreciated. Thank you all in advance!

 

Verify thermostat is opening and fans are coming on. With a HCI build you would inherently have a dyno tune as well at which point you can have the fans come on sooner if needed.

 

Thank you for quick reply Smitty. I did hear high speed fan come on when ac was on. Plus I don't belive fans, working or not, should b an issue cruising at 75mph? That should b more than enuf air passing thru rad to cool it down, no? I thought of the therm possibility of not opening as well, even as highly unlikely as it is as it's brand new but again anything is possible! Thank you for reply!

 

Also, l cant help the little voice in my head whispering l may have installed one of the head gaskets on backwards but l just don't see that happening as this is not
my first rodeo. ls there a way to rule this out without pulling the heads? Laser temp probe both heads? Let it idle until fans come on and see if it cools? Like l said,
l have never ever installed one backwards so l wouldn't even be aware of the possible symptoms. But thinking about it logically, if one was indeed on there backwards,
wouldn't the cooling system develop incredible pressure? Wouldn't the engine get VERY hot? The max temp the car got up to on the freeway according to customer
was 220 and then once he got off freeway it actually cooled down a few degrees. lf even one of the head gaskets was indeed on backwards, wouldn't the car get hotter
than 220?

 

Is the lower air damn in place to direct air up into the radiator?

You said the radiator is new so a dirty radiator is out of the question.

 

Yes the air damn is in place and both the Rad and and condenser are both new

 

You need to be sure there is no air in the heads. In my view, the best way to do that is to cut the small hose that goes from the throttle body to the passenger side top of the radiator, of the two hoses there, the small one.

This hose (about 1/4" inside diameter) comes from the coolant air bleed system pipes attached to the heads. Tightly plug the cut end going to the radiator and then connect the cut end coming from the throttle body and heads to a gallon container on the floor by the passenger side wheel. Start up and let the cooling system try to pressurize.

A stream of coolant and bubbles will flow into the container on the floor via the coolant air bleed connections to the heads and extended hose going to the container on the floor, as the cooling system tries to pressurize. My bet is that you will be surprised how long it takes for the bubbles to stop. DO NOT let the surge tank get low. Stop and refill from the container on the floor if necessary. I do this procedure every time I drain the cooling system, often more than a quart of coolant is expelled before bubbles from the heads stop.

When all the air is out, reconnect the cut hose with a 1/4" barb- barb connector and clamps, refill the surge tank.

Get 4 feet of 1/4" heater hose and a 1/4" barb- barb connector and clamps ahead of time.

 

thank you very much for the reply Jim. I will give that a try even tho I am suspect that that is the issue as I have let it go thru several warm up/cool down cycles and in past that is all I have ever had 2do! But who knows, maybe this one is stubborn! Thank you again Jim!

 

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