Don Terrill’s Speed-Talk

I have a closed system, the radiator cap is on a reservoir on the firewall, 30 psi cap

Ls1, w/ jones cam, 5.7 L nothing too crazy, has a stewart water pump, which supposedly only comes in clockwise rotation, but i bought it used, so not sure if someone modified

The steam ports all tie into the reservoir, front ones tie into the radiator also. Reservoir ties into the lower radiator hose. Double pass radiator with dual 12an inlets

Car just gets hot and doesn't seem to cool off, radiator is much cooler than the motor, and outlet is a lot hotter than the lower radiator hose. I thought it would be better driving instead of idling because of the under drive pulleys but it still got hot last night making some laps around the block.

Before I start taking it apart, any ideas? I don't think i left the water neck tapped off or anything but I'm going to start checking everything

The ARCA ILMOR 396 motors have a small vent on the water pump that ties into the steam ports, not sure if this would be better.

How hot is "hot"? LS1 engines normally ran at 210-230 degrees.

I'm not a fan of double pass radiators in any application, they cause too much inlet side restriction. On the other hand I have also never experienced one on an engine with a suction side thermostat. All the same, upper hose sigificantly hotter than the lower is an indication of a flow problem.

I shut it off around 215, it seems to keep creeping up

I’m thinking maybe an air pocket? Would that cause a flow problem? I’m going to try and see if I can’t purge the air. Come to think of it I have never ran it without a radiator cap if that matters. Just looking at the hose from the radiator to the steam port, seems like there could be a air there

Just throwing some things out there;
Is the engine tilted backwards a few degrees to 'auto-purge' any trapped air, or is this taken care off of with what you refer to as the steamports? (I haven't looked at an LS in close detail before).

You mention the radiator is cooler than the engine. Tells me the radiator is doing its job so it shouldn't be an airflow problem.
As a test, have you tried running the waterpump faster?

Overal ignition timing?

215 is considered normal operating temp. Not hot by any means. It's not considered running hot until 260+. Millions of LS engines run ALL DAY LONG at 215* and never skip a beat.

What makes you think that's somehow considered 'hot' and what damage are you convincing yourself that it's causing? It's not. 215 is barely warm.


They run those ARCA ILMOR 396's to 210+ during any NASCAR race, as well. If they run at 210+ the entire race, I doubt 215 around the block is an issue.

I guess it just didn't seem to level off

I ran the car today without the cap today, when I revved it up water ended up shooting out of the reservoir tank on the fire wall, not sure what caused this, maybe the radiator being restrictive?

I check the timing, shouldn't be going higher than 27*, which was the default on my holley efi

Could the headgaskets be leaking?

Have you done any web searches on bleeding an LS cooling system?

They seem to be prone to air pockets, hard to bleed and very critical for cooling.

https://www.bing.com/search?q=bleeding+ ... orm=MOZSBR

GARY C wrote: ↑Sat Sep 07, 2019 5:49 pm Have you done any web searches on bleeding an LS cooling system?

They seem to be prone to air pockets, hard to bleed and very critical for cooling.

https://www.bing.com/search?q=bleeding+ ... orm=MOZSBR

Only if you eliminate the air bleeds in the heads.

I prefer a four corner bleed but some intake manifolds like LS6 don't make it easy.

2 things, you've probably got air, and like others said 215 isn't hot. Vacuum bleed the cooling system with a tool like this. It will get all the air out.

https://www.amazon.com/UView-550000-Air ... 002SRH5G

peejay wrote: ↑Sat Sep 07, 2019 7:31 pm

GARY C wrote: ↑Sat Sep 07, 2019 5:49 pm Have you done any web searches on bleeding an LS cooling system?

They seem to be prone to air pockets, hard to bleed and very critical for cooling.

https://www.bing.com/search?q=bleeding+ ... orm=MOZSBR

Only if you eliminate the air bleeds in the heads.

I prefer a four corner bleed but some intake manifolds like LS6 don't make it easy.

I have never dealt with an LS I have just had some tell me this and have seen several engine build vids where they had over heating issues do to troubles with air pockets and difficulty of bleeding.