Hi all,
I thought I would post this question here since my engine is an LS5. The car is a 1970 Chevelle SS, but this question may get a more accurate response from you guys.
I wanted to get some opinions on my running temperature. The engine is 72’ 454 LS5 Vette engine. Rebuilt more less to stock specs except a performer manifold. Open system with a 4 core aluminum radiator.

I recently bought the car and it ran at 215/225 and one day tried the AC and it shot up to 240. Now it was a hot…I mean hot, 100 degrees, but still, 240 is never acceptable. I noticed the coolant was 4 ½” below the neck. I see things as cause and affect so used the heat up water until it boils test on the existing stat and it was bad. Replaced it with a new 180 degree and filled to 1 ½” below the neck and it was better, but still ran too hot. By this time the fan clutch was no longer tight. I replaced it with a Hayden sever duty and the temp did improve, but still ran a little warm. Noticed coolant wasn’t really puking out so replaced the radiator cap…bled it for air and it now runs 180/190 on a cool day (has not heated up again). With the AC on it shoots back up to 215/220 at 30mph, again a cool day, low 80’s.
Opinions if I am back in a safe range or if I need to keep trying? The water pump I honestly feel is good. No seeping, no noise. The gage is new, but factory reproduction.

Left side 90 degrees on the dash gage represents 110 degrees with the right side of the gage representing 40 degrees. Odd, but stock.
The senor is in the head, and started to read that temps in the head will be hotter than the manifold readings.

My last Chevelle ran 190 (1977 Suburban 454 block) at all times (manifold), so trying to get used to the new one. But I also know the LS 5 is a different animal and read it is supposed to run a little hotter.

 

My '71 owners manual states that 210F is normal on a hot day. Personally I like my cooling system to have a bit more margin than that. With an aluminum rad and electric fans my LS5 now runs 180F-190F, even on a hot day.

 

With 180* stat, I don't think your system should see anything over 200*F. Do you still have your thermostatic fan? If so, see if it is working properly.

With engine at full operating temps, pull car over to safe stopping place, open hood, position yourself so that you can see the rotating fan, then turn your engine OFF. When the fan is hot and the engine is stopped, the fan should not turn more than 2-3 full revolutions before stopping. If it continues to spin, the thermostatic mechanism in the fan is not operating properly and you are not getting adequate airflow through the radiator at slow speeds.

Also, when changing stats, I always just leave the radiator cap removed, then start the engine and let it get to normal operating temps so that the stat opens and coolant is free to flow throughout the system. That will allow trapped air to be expelled. THEN you put the radiator cap back on.

Another thing to check out: The front spoiler (under the nose) on a C3 is there primarily to direct cool air UP and in front of the radiator. If that spoiler is missing or significantly damaged, the car will run hot when the engine is "working hard".

 

Note the keyword Chevelle in the OP...

 

Yep, chevelle…I know a little out of place, but the Chevelle guys on the other forum seem to maybe be missing the LS5 portion. And I received some way out there suggestions…

 

anyone running a Hayden severe duty fan clutch? the 2797 is the only one listed for the 7.4, but someone said the other day it was for trucks. I mentioned they have a truck specific fan, but held the line on change it. If it was not correct why would Haden not list another fan?

 

it is running to hot keep looking

 

Advance the timing and use your vac advance connected to manifold vac.
Also get yourself a good quality laser temp gun and take readings at the manifold stat housing.

 

Those factory gauges arent the most accurate
I have the repop SS gauges in my 67. Certain sending units will read higher than others found that out the hard way too

Install a manual gauge under the dash temporarily and see where youre really at. I take it youre running a shroud?
You can get a cheap one for under $30

Running the AC will bump up the temps a good bit. 210-220 on a warm day isnt so bad.

 

ide install a mechanical gauge for just a day or 2, see how it reads against the factory one. and yes it will look hokey in there but its all for science and making sure there "is" a problem.

 

An IR gun would be easier, I'd think.

 

Throw a cheapy mechanical temp gauge and plumb it into the intake close to the thermostat housing. IR temp guns are very inconsistent and readings vary upon the coat on the surface you are shooting.. Also you want water temp, not metal temp.

I run a mechanical gauge and keep it hidden behind my console. I pull it out when I want to cross check my stock gauge. Factory gauges and aftermarket/repro temp sending units will read all over the map. Ironically, a repro temp sensor in my head and my factory temp gauge is within 5* or so of my mechanical.

Verify you actually have a problem, and then we'll go from there..

Btw I have a 650hp BBC in my 71' Vette that runs 180-185* with the AC on and it will idle at that temp all day on a 100* Houston day... So it is possible to get the temps down with AC..