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David H
David H, GM master certified
Category: Chevy
Satisfied Customers: 2678
Experience:  Cadillac Technician 18 years cadillac dealer.ase master master certified
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Chevrolet Camaro Z28 96 Z28, keeps overheating, replaced

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'96 Z28, keeps overheating, replaced water pump, thermostat, temp sensor, water pump on the head, 2 different radiator caps, trying to bleed air out of radiator. Replaced upper & lower hoses, check overflow hose, has had a recent head gasket replacement. With cap off & cold, coolant rises, doesn't bubble. No coolant in oil, no oil in coolant, doesn't smoke & tailpipes are dry.....HELP!!!!
Do the cooling fans work?
Customer: replied 6 years ago.

They are wired to come on as soon as the ignition comes on, but one on passenger side, squeals. But when "tapped", stops squeal.

Both fans come on at start-up.

With the fans running and the engine hot you should feel very hot air blowing across the cooling fans. Tbs radiator core itself should also be very hot. If not then the coolant is not flowing through the radiator. This could be a plugged radiator or an air pocket in the cooling system. You can also turn the heater on full blast with the a/c compressor off. If the engine temp. drops then you have a flow problem at the radiator.
Customer: replied 6 years ago.

Both hoses are hot. So it's flowing through the radiator.

When car is first started, coolant level doesn't appear to circulate with the cap off.

It slowly rises vs going down.


While driving, temp is fine until reaches normal operating temp's.

Then temp sky-rockets, extremely fast, & coolant comes out over-flow.

Accelerate to 2500-3000 rpm, temp drops for a very short time, then starts rising again.

Am able to only do this about 3 times before the temp stays in the red-zone.

I would suggest performing a block test on the cooling system to rule out a head gasket leak.
Customer: replied 6 years ago.

What is a block test & how do I do one???

What is it that I would be looking for??


A block test is a simple and inexpensive test using a blue liquid that turns yellow in the presence of exhaust fumes. The tester can be purchased at most part stores for about 25.00 dollars. Just make sure to lower the coolant level a few inches before testing to prevent coolant contaminating the tester.
Customer: replied 6 years ago.

So, the presence of yellow in the liquid will signify a blown head gasket??


If I try this & no yellow, then what??

I've been working on this for over a month now & am no closer to a solution.

They shoot horses, can I shoot the car??

If the head gaskets are not leaking then the cooling system has to have a restriction in flow.
Customer: replied 6 years ago.
Am running a block test right now.
If not yellow & seems to be a restriction in flow, I'm stymied as to where. I've flushed system twice so far in last month. Run all the hoses, all the lines, etc...
Let me know how the block test comes out.
Customer: replied 6 years ago.

Dye stayed blue. After being run for approximately 5-8 minutes. I can't run it longer without have the coolant drawn in.

Again I have flushed & cleaned radiator twice so far, drained & flushed with a hose, no evidence of rust, no discoloration, etc...

Replaced cap twice, replaced water pump twice, replaced thermostat twice & temp sensor in water pump twice.

Coupler between the water pump & cam seems to be turning.

Hoses & coupling's are all new & sound.


Turn the heater on full blast with the compressor off and see if the overheat condition is reduced.
Customer: replied 6 years ago.

It has & doesn't change.


But, noticed that there is a line coming from the back of the head to radiator.

Is this line supposed to have coolant coming from it & going to the radiator???

That is the coolant air bleed pipe.If coolant is not flowing out of this pipe then you have a flow problem.
Customer: replied 6 years ago.

With a reverse flow system, the goes to the head first, line connects drivers-side head to the passenger side head, with banjo bolts.

Then runs along side the valve cover, line would normally go into throttle body & then from throttle body to radiator. But throttle body was by-passed. Air bleed line goes to heater core & am getting coolant there at the bleed vavle.


When I flushed the radiator, was able to flush water through upper hose & cycled through water pump & out the bottom of water pump.


How could I know (a) if by-pass is affecting or (b) making sure the block was flushed completely??

Did you mount the t-stat in the top of the waterpump housing?
Customer: replied 6 years ago.
Yes, I assumed that is where it went since that is where I took the old one out when I replaced it.
Yes that is the right place,just making sure.Are you saying the air line was bypassed at the throttle body and rerouted to the heater core?
Customer: replied 6 years ago.
No. there was a 90 degree elbow on the passanger side of throttle body. It was leaking, so I was told about a throttle body by pass, the hose that was going from radiator to the drivers side of throttle body was taken off and connected to the line that ran from the back of the head. Now no coolant lines run through the throttle body, it only runs from the back of the heads straight to the radiator. The line to heater core with bleed valve is not involved, the question is, should coolant be coming from the back of the heads in a line that would go threw the throttle body then into radiator? i think it is supose to but i have no coolant geting back to the radiator
Yes that line should have free flowing coolant,It is there to heat up the throttle body in cold weather,important if very cold outside and to cool the throttle body when very hot.I am starting to wonder if the waterpump gear is properly connected to the cam gear.You should have major stream of coolant from that line.An air pocket will also cause this issue and this engine is one of the worst for air pockets.The only way I fill the cooling system is with an air lift kit but this requires an air compressor.
Customer: replied 6 years ago.

How would I be able to tell if the w-p gear is properly connected to the cam gear??


We'll take this a step at time, so far have gotten further with you good folks, then with anyone else.

Remove the radiator upper hose then start and rev the engine.Coolant should pump through the hose.You will need to remove the t-stat and make sure to put a constant flow of fresh water into the cooling system to do this test.
Customer: replied 6 years ago.
Remove the upper hose from the water pump or the radiator??
From the radiator only because you can point the hose where you want to control the flow.With the t-stat out and the engine rpm's up there should be a strong steady flow stream.Just don't let the system run dry.
Customer: replied 6 years ago.

Please clarify a bit more...

Take the hose from radiator, leaving the t-stat in?? while revv'ing. Or take t-stat out first & then run test??



Remove the t-stat for the entire test so you won't have to get the engine hot.After the t-stat is out then remove the hose and rev the engine while putting a water supply into the cooling system.This test is to measure output from the waterpump.
Customer: replied 6 years ago.

Running that test now, please be patient.


No problem.
Customer: replied 6 years ago.

Ok, here's problem....My upper radiator hose is lower then my t-stat & water pump, so the w. pump is empty.


In order to check the flow, where should water be run?? At the t-stat opening or the radiator cap??

I meant to say after removing the t-stat put the seal and housing back in place and tighten the t-stat bolts again for the test.The waterpump pulls the coolant from the radiator through the other hose.You need to keep the radiator full of water at the radiator cap.
Customer: replied 6 years ago.

Done. Excellent flow through the water pump.


What's next??

Remove both hoses from the radiator then force water through the upper hose inlet and check for good flow through the radiator core.The water should flow free and with lots of volume out the other side.
Customer: replied 6 years ago.
Checking now.
Customer: replied 6 years ago.

Ok, have mainly flow coming out water pump because of a 2nd, lower hose that goes to the pump.

Still has a decent flow coming out the main, lower radiator hose.

Looks like you are not getting all of the air out of the cooling system causing an air pocket.This will cause a complete loss of flow.I have had this happen to me many times.That is why I now only use an air lift to draw the cooling system to a vacuum then using the vacuum to draw the coolant into the radiator.If you can't get this tool then try filling with your 50/50 mix coolant until full.Do this with the bleeder open until coolant flows out of the bleeder.This may take a while.Once the system is full start the engine and run until the t-stat opens.Just let the engine idle to warm up.Then turn the engine off and remove the radiator cap.Let the engine completely cool back down preferably overnight.Then refill the coolant level until full.This should remove the air from the system.
Customer: replied 6 years ago.

If the bleeder's are open, won't it draw air in while starting??

& if bleeder is open, when started, it's just going to blow all the coolant out??


The top bleeder sits above the radiator cap, they laws of gravity/ physics says that the coolant will not get above top of radiator, ergo, always having an air pocket???

I have found that using the bleeder is only useful with the engine off.Retighten before starting the engine.As the cooling system fills up the air will be slowly forced out of the bleeder.The pressure of the coolant will eventually work its way out of the bleeder.This process takes a while to do.
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Customer: replied 6 years ago.

Ok, car doesn't over heat until thermostat opens & engine temp goes straight from 180 to 260.

Then coolant begins to slowly rise until it comes out the overflow.

Did you do the head gasket block test at idle?
Customer: replied 6 years ago.

Yes. Have followed all of y'all's directions.

Ran it for approx 5-8 minutes, dye stayed blue until a little bit of coolant got sucked in.

But repeated the test & dye stayed blue.

Try lower the coolant level down more and this time rev the engine with quick snap throttle lasting a few seconds at high rpm.This will test for a smaller head gasket leak at higher rpm's.
Customer: replied 6 years ago.

Running it with the dye??

Did that with the dye, soon as it hit higher rpm's & released accelerator, it started to suck up the coolant into the dye.


What would I be looking for, exactly??

Sometimes when the head gaskets leak they only leak under extreme pressure like high rpm's.If you drain out most of the coolant and do the test again but only for 30 seconds or so.This is a simple diagnosis really.Either the head gaskets are leaking exhaust fumes into the cooling system or the coolant is not flowing through the radiator.
Customer: replied 6 years ago.

Ok, I will try that in the morning. Been at this all day long.

Again, I greatly appreciate all the help & y'all will probably be chatting with me again

tomorrow. problem.