Hot-running LS6
 

Anyone have any tips on lowering the highway speed temp on an LS6 with 4.10 posi, M22, polyglass rubber and otherwise stock? The car runs at 190-210 at speeds of around 65-70. Plenty of coolant in the radiator, car has never overheated or belched up coolant. Everything seems to be functioning okay. Am I driving too fast with this gearing? Any thoughts?

Re: Hot-running LS6
 

Is Your Fan Clutch working properly?
What is your Thermostat rating?
What weight engine Oil are you using?
Also try Flushing the Entire Cooloing system.Get it all out of there.You'd be amazed what kind of Crap can accumulate.

Re: Hot-running LS6
 

[ QUOTE ]
Is Your Fan Clutch working properly? <font color="blue">I think so </font>
What is your Thermostat rating? <font color="blue">Don't know, good question </font>
What weight engine Oil are you using? <font color="blue"> 20W50 nonsynthetic </font>
Also try Flushing the Entire Cooloing system.Get it all out of there.You'd be amazed what kind of Crap can accumulate. <font color="blue"> Makes sense, although the coolant looks fine and it was changed recently </font>

[/ QUOTE ]

Re: Hot-running LS6
 

This seems to be the normal heat range for an LS6. If someone knows how to get them to run cooler I'm listening.

Re: Hot-running LS6
 

My 70 L78 TH400/4:10 was running 210+.
I checked all I mentioned earlier,and then Changed my gas blend.I run highest the station has at the pump,then add Protek Lead/Octane boost.By verying the mixture,I found it actually showed an Increase/decrease in my cooling system Temp.
Albeit slight,but still a difference.
Today I found the best is 20 Gallons of Mobil gas,with 11 oz.Protek additive.
I only run 185-190 degrees now.

Re: Hot-running LS6
 

Interesting guys. I am running between 200-210+ with my LS5 TH400. Rick I have done all the fixes you mentioned including boiling the tanks &amp; recoring my original radiator, changing to a Mr. Gasket 160 thermostat, and am running 20W50 Penzoil. Would the timing be an issue?

Re: Hot-running LS6
 

Yes Frank.
Timing is a Factor.What are you at?

Re: Hot-running LS6
 

Rick believe it or not I have never adjusted the timing under my ownership for over 2 1/2 years and 12000+ miles! The car has run perfect and has had not had ONE mechanical failure or problem in that time! (knock on wood) So I am not really sure. [img]/ubbthreads/images/graemlins/blush.gif[/img]

Re: Hot-running LS6
 

I would check the Gauge first to make sure it is correct!Sometimes the gauges are not CORRECT! then the timing,and then use a 160 or 180 degree ROBERT SHAW thermostat.I had a slight overheating problem and worked with the timing,and change to the Robert shaw thermostat and lowred my temp 10 degrees.Please do not try the coolant additives such as WETTER WATER and PURPLE ICE,They do not work!If you have not flushed your coolant system in the 2 years I would think you should do that also and use a good brand of coolant.Hope this helps

Bobby

Re: Hot-running LS6
 

I have similar setup as yours,but with more cam, 11.5:1 no clutch on my fan and my car never over heats,I have a 160 degree thermostat,38 degrees total timing and run pure 100 octane fuel, the car never gets over 185 degrees no matter how hot it is....

Re: Hot-running LS6
 

190 to 210 isn't unusual for these cars. If I recall correctly the OE thermostats were in the 185-195 range. I replaced mine early-on to bring the temp down.

We attended the Street Machine Nat'ls the year it was held at Gateway in E. St. Louis and were trapped in the gridlock trying to leave on Saturday afternoon. My battery wasn't doing well and I was afraid the car might not restart so we let it idle for over three hours. The car never once got above 165. That was with Turbo Blue in the tank and timing at 2 degrees advance. Yes, timing can be a factor.

Another thing to check out is your water pump. I have a friend who built an L-88 for his '69 Chevelle and had similar trouble. He installed a new four core radiator but still no help. Finally tore into the water pump and found the fins on the impeller were about half the size of the ones on the other pumps he had used. Changed pumps and the problem was fixed.

Just some thoughts. [img]/ubbthreads/images/graemlins/dunno.gif[/img]

Dennis

Re: Hot-running LS6
 

Interesting responses with some good tips. Sounds like MOST folks are saying that "these cars run between 190 and 210 (and up)" so that performance shouldn't be shocking. However there are things one can do to chip away at the cooling system performance. I appreciate the tips and hope to see more; I'm sure we could all learn a thing or to about the "norm" of these cars. I have owned an SS396 for years but am new to the LS6, so I don't yet have a "vibe" for the "norm" for the car. [img]/ubbthreads/images/graemlins/confused.gif[/img] I'm getting there though...

Re: Hot-running LS6
 

Lots of good answers on the topic at hand. Thermostat, good system check, and timing check should all be on order. Timing plays a big factor, but if it starts/runs well, then you should be close. And, the range you describe is normal for these cars. Heck, that's actually a little cooler than where some of the newer cars run. One thing that is easily overlooked, though, is "pressure". Any idea what radiator cap is on it?

Care for some food for thought...?

Low coolant temperatures DO NOT necassarily indicate a well functioning coolant system. If there is no heat transfer between the metal and coolant, then you've got the low coolant temp you're looking for, but you're engine's temp is actually higher. If there is heat in your coolant, then it's doing it's job. Something else that is of help is to get an infrared temp gun and check and see what the engine's temp is actually at, versus what the coolant temp is. If the coolant isn't taking the heat away, but is giving you a low guage reading, then that's really just a fasle sense of security...

Re: Hot-running LS6
 

Our '69 L78 4:10 geared Chevelle runs in the 205 range on the highway in hot weather. You are running a lot of rpm at 60 mph. The temperature will stay below 200 at idle. Never had a problem in 21K miles. Total timing will make some difference.

Re: Hot-running LS6
 

[ QUOTE ]
Lots of good answers on the topic at hand. Thermostat, good system check, and timing check should all be on order. Timing plays a big factor, but if it starts/runs well, then you should be close. And, the range you describe is normal for these cars. Heck, that's actually a little cooler than where some of the newer cars run. One thing that is easily overlooked, though, is "pressure". Any idea what radiator cap is on it?

[/ QUOTE ]

<font color="blue"> Great tips Rob. Everyone has had something good to add, and if you add up all the responses, there is a great body of knowledge on supercar cooling systems here. As far as the radiator cap, it is a repop of the original GM cap from Ground Up Restorations. </font>

Re: Hot-running LS6
 

Things that help:

good radiator cap.....for every 1 lb pressure the boiling temp raise is aprox. 2 degrees.

16 lb cap working properly will raise boiling point to aprox. 244 degrees.

Car operating at 200 is still 44 degrees below boiling point.

Antifreeze/antiboil raises this boiling point also.

Higher octane fuel makes alot of difference...not sure how much but the difference between 96 pump and 110 race fuel is tremendous.

Less timing lowers operating temp but also hurts performance..there is a happy medium

Things that hurt:

Low pressure or leaking radiator cap.

Weak antifreeze

Low octane fuel

Lean fuel condition

Too much timing


I have seen alot of times that someone will take a thermostat out of a car and it run hotter....so in saying that...if the flow of water is too fast it doesn't have time to cool properly, but on the same hand if it is too slow it won't either. Use one of the new

Clutch fan should not affect any driving speeds over 40 mph or so.

And last but not least.....DON'T TRUST YOUR GAUGE....either check temp with a thermo gun or an old fashioned thermoter in the rad.

Hope some of this helps.

Re: Hot-running LS6
 

------Us guys with big block Corvettes have suffered forever with different over-heating issues.All of the above mentioned are important.The infrared gun will really help you out.Shoot it somewhere near the sending unit and then check against the guage.The sending units sold today and even old ones are calibrated differently than the original one that came in your engine.You may be actually running cooler than you think.If you find this to be true get a Corvette Central catalog(or www.corvettecentral.com).In there somewhere you will find a little infinetly adjustable inline electrical "dohickey" (technical enough for you?) that,once installed,you can adjust the guage reading to read correctly.It doesnt cost too much and will keep your guage reading correctly forever.Hope this helps as it is a real slick little unit..............Bill S

Re: Hot-running LS6
 

190 on the hiway seems reasonable, but over 210,and you do not hear the fan clutch start locking in and pull the temp back down... i would be looking for a restricted radiator.if the radiator is not dumping heat off to the fan coil then the fan is not going to engage,if the radiator is plugged it wont transfer heat.another thing to watch closely is these systems get alot of air pockets in them whenever the cooling system has been worked on or drained, it is important to work the air out while the engine is idling and the t-stat is open, by pinching off the upper radiator hose on and off for a few minutes, this will help purge the air out of the system [img]/ubbthreads/images/graemlins/beers.gif[/img]

Re: Hot-running LS6
 

All of the above mentioned items are necessary for a cooler running engine, but some more things are necessary for everything to work properly. Make sure all of your shrouds are in place. Your fan shroud and fan position in the shoud is important. You need to have about half of your fan outside of the shroud so that it is pulling the air through and not just swirling inside. Also, the attachment under the radiator that protruds out. I have found that if I run my car over a certain speed without that piece in, the temp rises quickly. The air is searching for the path of least resistance and sometimes it will go under the car instead of through the radiator where the water can be cooled.
A clean radiator and block, proper functioning water pump and fan clutch, properly positioned shrouds, and a good flowing thermostat (Robert Shaw) will make any system work as intended.
Another piece of advice. Whenever you flush or change out your coolant, add back in a can of waterpump lubricant/anti-rust. This is one thing that is added at the factory, but is lacking in all antifreeze mixtures. Helps to keep all of the cooling system operating properly for a long time to come! [img]/ubbthreads/images/graemlins/naughty.gif[/img]