First off this is on my 96 formula, 355, le3, full bolt on, csi electric water pump, 3.42's, and a th400. I've owned lt1's before and worked on A LOT of them for years now and this one has me baffled as why it's overheating. I've never had one heat up like this before.

I only ran the car for about 100 miles with the 4l60e when I put in this motor before I switched to the th400. During that 100 miles I don't remember it heating up at all, even though the 4l60e didn't have OD and I was turning 3000rpm down the highway. When doing the th400 install I did pull out the plastic panels that go in front of the radiator(not the air dam), but I've taken these out of a bunch of cars and never had an issue. This is the only piece I haven't put back in yet since I don't have it anymore, and am looking for another set of them.

I did the th400 swap about 4 months ago, and up until I pulled out the heater core this last weekend it never heated up this bad. It would always run warm going down the highway, about 215ish, but would cool back down to 175ish when I got off the highway.

Right now it's about 90 degrees out here, and off a cold startup, it will warm up to about 175 and will idle and stay there forever if I don't drive it. As soon as I start to drive though it will go up to about 200 degrees, and will never come back down below 190ish, even if I stop and let it idle. On the highway though it will heat up to 220-230, as I turn about 3000rpms.

I've swapped radiators about 2 months back because of a crack in the other one, and it didn't change at all the temperature. I am running no a/c, no p/s, no front bumper support, and of course now no heater core and looped lines on the water pump. I just added water wetter yesterday and another big transmission cooler, both of which didn't help any. I am bypassing the stock transmission cooler thats in the radiator also.

I replaced the thermostat about a month ago, and now am running a modified thermostat that is open all the time, but still is a restrictor. I do also now have both fans wired up hot anytime the car is running, but this didn't help any. I have no fog lights and the holes are open to get even more air in.

All my lt1's in the past have ran about 170-190, even on the hot days, even my turbo setup only ran in the 190 range. I run about 80% water 20% coolant right now, have had 50%/50% before, but nothing helps. I've bled the system many times and have bled lots of lt1's before so I'm not new to this. The block is out of my old car so I know its good, and the car has a full dynotune on it.

Any ideas would be great, this one has me lost.

 

Those panels keep the air flowing into the radiator. That is the first thing I would put back (no matter what it did on any car you had in the past).

 

Agreed. That or the electric water pump can't keep up at rpms.