Yes, I did search in case anyone wonders. I'm also pretty mechanically adept in life, I do it for a living. But this one has me stumped.

Recently, my car was running hotter than normal around town and at highway speeds. To remedy this, I bought and installed a brand new LT1 (SLP HD) radiator. The car currently has a mix of Dex-Cool, distilled water, and Redline Water Watter. Everything has been bled and completely topped off, and I do not run the A/C (although I do have it and it works).

Here's what I notice:

Startup and initial driving: 165-175*
Cruising under 70mph: 175-185*
Cruising 70-80mph: 190-195*, and it quickly gets there
Cruising 80mph+: 200-220*

This is under 1/3 or less throttle, and once I reach these temps, they usually stabilize around 190* when if stopped at a light or under lighter speeds. It used to be that the car never reached above 180* even on the hottest days. The only mods performed recently are the LPE/Weiand intake, ported 6.0L heads, and a rebuilt 4L60E.

Yes, my air deflector is still intact. This is a recent issue (thus the new radiator). I run a 160* t-stat (four years old), the above-mentioned coolant mixture and radiator, and nothing more.

Why does my coolant temp increase in direct proportion to my cruising speed, the not go back down very much? This is annoying as all hell, and this is not "normal" as some of my friends like to think it is. I know my car, I know how it runs and how it's performed in the past, and this is not right.

What I'm looking at doing:

Removing the thermostat
Removing the fan cut-off at 65mph
Draining and refilling my cooling system with more water, less coolant, and Royal Purple ice ****

I'd really like to get this resolved in the next few weeks before the Pontiac Nationals. Thanks.

 

Do you have an auxillary transmission cooler?? If you do and it's a large enough capacity, make sure you just run the tranny fluid through it and bypass the one in the radiator. I noticed about a 10 degree drop in my running temp after bypassing mine. Also, I wouldn't recommend taking the thermostat out, it shouldn't be causing an overheating problem unless it's sticking partially closed. All the thermostat does is set the minimum temperature the engine will see and help the car reach operating temperature quicker. If it's four years old, I'd highly consider replacing it anyway.

 

Yes, I do run an aux cooler for the tranny, a 50K GVW B&M. Yes, I also run it in tandem with the stock cooler located in the radiator. I have been debating on running the aux only, I guess this is a deciding factor.

I've thought about replacing the thermostat, but at $60 a pop, I don't wanna start throwing parts at the car unless absolutely neccesary.

 

Anyone have any other suggestions? I'd like to knock everything out at once...

 

im having a very simalr issue but mines also starting to do it more around town as well.

 

Hey my 98ss overheats like a bitch, i have the 160 stat to. I put that redline water wetter stuff in the radiator to "lower my temp by 10-20 degrees".......bull, thanks for wasting my 12 bucks. My car also has an aux. tranny cooler and my temps sound identical to yours. My tranny temps go up in the 200 range when driving on warm days doesn't matter what the speed. Where is your tranny cooler located? I was thinking of getting an electric water pump that ran all the time and also the electric switch for continuous fan control. I am looking for the same answers as you, anoying when you can't drive your car very far or for very long isn't it?

 

maybe its innefecient cooling to the radiator?

 

i put ground effects on the car, do you think the front spoiler messes up the airflow at all?

 

The stock chin spoiler keeps air from going underneath the car. In doing so it creates a low pressure area behind it. Air pressure likes to be balanced or equal wherever it is, so the high pressure area in front of the car seeks the low pressure area underneath the car. How does it do this?? It chooses the path of least resistance...through the grill opening and the radiator. This is why cars that have had the chin spoiler removed tend to overheat at higher speeds. In answer to your question, no I don't think the spoiler is messing up your airflow.

 

too hot of a spark plug and ignition timing can make a engine run noticeably hotter. i'm pretty sure that u have already cleaned your a/c condensor with a psi washer and inspected all the fins but good luck!

 

4 inch deep aluminum trans pan = 3qts more fluid = less heat

I use 66/33 dex-cool mix, 160* thermostat, B&M stack plate type trans cooler, and a 4 inch deep aluminum trans pan. Trans fluid runs 176* normal driving, and after a 130 mph pass on a 89* day a few weeks ago, the temperature went up to 187* then cools back down accordingly. All this is good and within the limits. Also check your timing, or its possible you have a hose that is collapsing under High RPM driving, slowing the coolant flow. Check (Lower Hose) Rev the engine in park and visually look at the lower hose for any collapsing. Good Luck!

 

just slow down!...really, id check the condensor for dirt/bugs. i try to clean mine every now and then at the car wash. gets you a little dirty crawlin around on the ground, but if you've never done this, you'll get some nasty **** outta there.

 

running lean?

 

I've taken everyone's suggestions to note and will go through everything again.

As for being lean, quite possible since I'm running an unrefined 60lb injector tune (although from Jesse Bubb), and the car needs a fresh tune from scratch.

Tomorrow will see:

1) Coolant drained and refilled with a better mixture
2) New thermostat (Be Cool has a new one out)
3) Re-route my tranny fluid through the auxiliary cooler only
4) Re-check all hoses and the condensor, although it looked fine when the radiator was out a couple of weeks ago

 

I was going to suggest the lean (detonation?) thing too, that will certainly cause heat. If you've got HPT, I can look over your tune and see if anything looks like its set up out of line.

Also, check for the common symptoms of a head gasket problem.

 

I would bet it is the thermostat. I had a similar problem only my car ran hotter (230 ish) at highway speeds. When I slowed or even stopped the temp would come down somewhat but not all the way to normal. more work = hotter engine, especially if it is starved for coolant. Turns out that the thermostat failed closed. Replaced it and problem went away. just my .02

 

Read through both pages of this thread. My system was muddy as hell, now it's clean as a whistle and been that way for about 35k miles. Might as well scrub/flush it if you're going to be draining it. Even if it doesn't help your problem, it's still good practice and definatly NOT going to hurt.

https://ls1tech.com/forums/generation-iii-external-engine/476478-dex-cool-coolant.html

 

I could see the inefficient radiator thing, but I can't see the stuck thermostat thing. If the thermostat was stuck, it wouldn't unstick just because you went below a certain speed.

Here's another thread on flushing your radiator too...
https://ls1tech.com/forums/showthrea...14#post3360114

I may flush mine out and replace it with the green just because of Blur's thread along with this one. I don't want sludge forming in my engine... ever, for any reason.

 

You really shouldn't run the green coolant. I still run dexcool and it's clean. I've drained and replaced the coolant twice since then (heads off, then cam swap later). The other day I yanked the thermostat for a 160* and it lost some so I filled it back up. Old thermostat had never been out of the water pump before and it looked as nice as the new one.

 

Hmm, maby I'm wrong about green coolant being bad? I've never had a problem with dexcool and I don't even use distilled water, mine comes straight outa the hose.