Ikes 91Z

Hey all, this is my first post on here. Excited to be a new ls1 owner...

Here's the skinny...

Swapped in an ls1 into a 91 Z28. And it is overheating. Here is what I have done/looked at.
1. Swapped tstat for good measure
2. Elevated front end, ran the car til it warmed up with heater on full blast to push air pockets out of engine/heater core
3. coolant stays full and there are no leaks anywhere.
4. The water pump isn't leaking anywhere, and has no play on the pulley.
5. Dual electric fans kick on

I'm really just at a loss as to what else to try so I can finally get on the road and drive the car! Any help would be appreciated.

Pop N Wood

iTrader: (1)

Is it overheating while driving or while idling?

When moving you really shouldn't need the fans.

What radiator do you have? New?

Jack the front of the car back up again and unbolt one of the steam vent plugs until water comes out. That will guarantee all the air is out of the motor.

Old Geezer

iTrader: (3)

What do you consider "overheating"??

Ikes 91Z

It overheats during idling, and continues when driving. The radiator is a stock 3rd gen radiator. It worked fine when the old engine came out. And has the capacity to keep this one cool. How high up would you recommend me jacking the front of the car up? Currently the tires are up about an inch off the ground, I would think that's enough but I could be wrong.

And by overheating, I mean continuing to climb until hitting the red and I shut the car down.

Pop N Wood

iTrader: (1)

Get the top of the radiator above everything else.

Does sound like air in the system. You may need to burp it a couple of times. Pulling the steam vent plug will get all the air. They are o ringed so no worries about hurting anything.

What fans? Are they well shrouded?

Ikes 91Z

They are the stock dual electric fans from the third gen.

I will try and bleed it that way again. I've tried a couple times. I will jack the front end up quite a bit higher to see if it helps at all.

Thanks for the help so far.

sowbelle

Do you have coolant on both sides of the t-stat?

gofastwclass

iTrader: (2)

What is the actual coolant temperature? Being a swap and depending on several factors, your gauge could read red, but the engine could be fine. For example a stock 2002 Trans Am WS6 low fan comes on at 226° F (108° C) and the high fan enables at 234° (112° C). These engines typically use a 197° thermostat. There are 180-ish degree and 165 degree thermostats available. I can tell you from first hand experience the 165° is too cool for winter driving.

That is much hotter than we used to want in the carburetor days, I used to freak out at 195 - 200. Hahaha.

Steven32

BANDIDO79

Listen to that man^^^. i just did what popNwoods recomends. I did not have water circulating on my lq9 79 trans am. Did as above and my car now runs at a constant 200-210 with stock 86 celcius thermostat.. with stock 79 trans am radiator. most likely you dont have water behind the thermostat.

BLKMGK

Accessories running as stock or reconfigured? Positive that I the pump is spinning in the right direction? Is the top hose hot, lower?? Radiator hot? Source of water pump, is it new or used from donor?

Ikes 91Z

The accessories are all stock including the water pump (or at least it's the original from the donor). I am in the middle of swapping out the water pump since it's only $150. I am then going to follow the process mentioned above about the steam vent plugs when I refill it with coolant.

Ikes 91Z

Well I don't think it was the water pump. Swapped it out, refilled the coolant and tried bleeding it doing the vent plug process and still can't get it to quit overheating. It doesn't even look like the coolant is circulating. Maybe I'm crazy. I don't know at this point.

1964SS

iTrader: (1)

Stock gauge? What temp sending unit are you using?

Ikes 91Z

Stock 3rd gen gauge and am using a stock cts for a 99 ls (3 wire design).

BANDIDO79

are you using a stock thermostat they are 86C or 186F but checked recently and it opens up at 195F.. when you say that its overheating what is the reading it? takes more than a few minutes for that thermostat to open up. prior to that water will not circulate.

Ikes 91Z

Yep. Using a OE thermostat. I'm letting the gauge read 240ish before shutting it down. Usually runs for about 10 minutes before it hits that temp, so it is a slow, steady build in temperature.

BANDIDO79

240 is high.. I would verify to see if your gauge is reading correct with an old scool mechanical gauge.. i placed one on my water pump just to be sure my stock 2nd gen's was reading right.

1964SS

iTrader: (1)

Does the PCM see the engine overheating as well? Just wondering if the sender is even compatible with the gauge. Hook up a scan tool and verify the temps. I use the elm obd readers with my torque pro app. on my phone.

slogo

Put a aftermarket gauge on, with the correct
sending unit for the aftermarket gauge.
That will tell you if engine is actually getting hot.