'67 L71 Temperature Control

[Harvey W.]

While all of you have been enjoying the National Convention in Mobile, I have been driving in 95F Connecticut. My '67BB is not happy in this weather. While it has behaved this week, extended driving in high temp/humidity produces dangerously high temps. I don't want to damage an original big block motor and so am looking for suggestions.
When driving to Carlisle last year on a beastly day temps hovered in the 220-230 range. Very scary. I made it, but was terrified of an overheat and engine damage. I have stared using a product called -32 which seems to help but extended running in high temps produces higher temps than comfortable.
My question is what is a reasonable cure for a car that has been driven and maintained but not restored and which will continue to be used the same way.
Auxiliary fan?
Dewitt BB reproduction radiator?
Other additives?
Thanks for your help.
NCRS Rocks!!

Harvey Wooding
Member # 32769

[Stephen L.]

Re: '67 L71 Temperature Control

An Aux fan won't do much above 25 mph. The air flow entering the radiator while driving is the primary coolant.
I'd begin by a good flush of the system.
If the problem continues you might "recore" the radiator, preserving your original tanks. A good radiator shop can do this.... Keep in mind that a "flush" could cause a leak in the heater core......... If the heater core is original you may want to install a bypass hose on the heater core before flushing.......

[Duke W.]

Re: '67 L71 Temperature Control

The first thing you should do is convert the ported vacuum advance to full time, and you will need a 12" B26 VAC to replace the OE 201 15 or whatever is there now. This change has been discussed here many times, and it will primarily reduce coolant temperatures in low speed stop and go traffic with lots of idling.

If high temps are common at cruising speed above 35-40 MPH then the radiator is suspect. Remove the cap and drain enough coolant to see the ends of a few of the top tubes. Do they have deposit buildup? If so then the radiator either needs a rod-out or a new core.

There's also an easy fan check. When the engine is cold it should take very little force to turn the fan. At very high temperatures when you shut down the engine the fan should require noticeably more force to turn by hand. Further, when it's very hot open the hood, have someone rev the engine to 2000-2500. Feel the airflow and note the amount of "fan roar". Do this again right after a cold start and compare the difference.

Also test the radiator cap. Does it hold 15 psi? Most parts stores have a cap tester at the counter.

Forget the snake oil additives and aftermarket stuff. Your car is over 50 years old and it just might be that some important cooling system components are not performing as well as they did when new. Get them back to "as-new" condition and temperatures should cool down.

Also understand that the NORMAL operating temperature range is 180-230F. The thermostat keeps then engine at the minimum operating temp and getting over 200 is common in hot to warm weather, especially low speed driving.

With a 50/50 blend of ethylene glycol antifreeze and water and a 15 psi cap the boiling temp is 265F, so unless it's puking coolant out the overflow hose it's not really overheating.

Duke

[Mike T.]

Re: '67 L71 Temperature Control

Harvey - Maybe I missed it but have you had the chance to verify the dash gauges reading with an IR gun? There have been a lot of articles written about how the coolant temp sending units have changed over the years and bottom line, the new one just don't read as accurately as the older ones did. A number of years ago, one temp sending unit that got good reviews was the Wells or Standard Products TU-5. Over the years, I've bought them from various FLAPS but these days, the one that seems to be 'close' to reading correctly...well, most of the time, is the Standard Products TS-6. Got one in my 66 L72 Roadster and it does read pretty accurately if the ambient temp is around 70-80 but if the daytime temps rise into the mid 90's, the dash gauge shows something up around 215IMG_1138.jpg66 L72 396 Dash Gauge - IR Gun Reading 196.jpg
when the IR gun shows the true temp to be 196 degrees.
Sorry for the sideways pics, not sure why this happens.

[Harvey W.]

Re: '67 L71 Temperature Control

All great info. This gives me some homework to do. My concern has been at hghway speed in hot weather the temp will run up to 230. Just seemed to high. Will do these diagnostics.
Thanks

[Harvey W.]

Re: '67 L71 Temperature Control

I am thinking a recore might be in order. The car has been maintained but also has had some extended sitting time over the years.

[Harvey W.]

Re: '67 L71 Temperature Control

I have a friend that I think has an IR gun. Will give that a try. Certainly fixing a sensor reading incorrectly is an easy fix.
Thx

[Stephen L.]

Re: '67 L71 Temperature Control

You can get your own IR gun for about $20 at Harbor Freight.....
Please keep us informed of your results.

[Harvey W.]

Re: '67 L71 Temperature Control

There is one near me and I'll stop there the next time I pass it. Will let you know what the gun says.

[John W.]

Re: '67 L71 Temperature Control

Test upload of picture.

196.jpg

[Harvey W.]

Re: '67 L71 Temperature Control

This is why I love NCRS. I am no newbie to Corvettes but never had the time to hone mechanical skills. I often say I no enough to get in trouble but not enough to get out. Anyway, when I have a question there are always multiple members chipping in with great suggestions and insight. When I drove to Carlisle last August and several times since in hot weather the gage was hitting the yellow caution zone. I would have been happy if it read what the picture provided shows. Made me VERY nervous. I hope I am well enough armed now to head off any future issues.

[Daniel S.]

Re: '67 L71 Temperature Control

How about a new Milodon thermostat? Milodon owns the original Stant Manufacturing design/patents, etc.

[Harvey W.]

Re: '67 L71 Temperature Control

Thanks. The thermostat is one thing on my list to check. I really don't think that is i since I do not get aa aloo out serious overheat but if it is not working correctly I'll replace.

[Daniel B.]

Re: '67 L71 Temperature Control

I did what Duke recommended a few years ago (THANKS DUKE!) and it did wonders to reduce overheating at idle and in stop & go traffic. I have not had overheating issues at speed. I also advanced the timing to a few degrees before detonation is evident when lugging under load, which in my case was 51 deg BTDC (all in w/vac) at speed. Adjusting the timing to optimize at speed resulted in 19 deg BTDC at idle w/o vac, which it runs very happily at and is dramatically advanced relative to the spec value of 5 deg BTDC for the 427-435 L71. My understanded is the spec idle timing value was deliberately retarded as a rudimentary emission control method to make it run hotter and burn off additional hydrocarbons.

[Skip N.]

Re: '67 L71 Temperature Control

Experience with my 1967 L68 427 Vette recently tells me

- BIGGEST difference was the Dewitt Alum Radiator (painted matt black to fool the NCRS newbies

- then REMOVE Frt bumpers (on Air Cond C2s they moved the license plate ; BETTER to just remove the bumpers - MORE Air Flow the better)

- lastly use the Stewart High Flow Cast Iron Water Pump ; with machined impeller

NOW I run at 190-195 on 90 degree days!

I understand these changes are ANTI-NCS, but that is what it takes to get high compression C2 Big Blocks to COOL with crappy modern fuels