jjhoneck

Driving my new (to me) C3, I have been surprised to note that the engine runs hotter at faster speeds.

At idle, and speeds below 60 mph, the temperature gauge stays to the cool side of 220. I'm guessing (since there are no numbers) that it's in the 180 - 190 degree range.

At speeds from 60 to 70, it will peg at 220. At sustained speeds of 80 or more (God bless Texas highways!), it goes above 220, into the 240 range. (Again, I'm guessing, since there are no useable numbers on the gauge.)

All of these numbers are "in the green" on the gauge, so I'm not overly worried -- but I'm surprised to see the temperature going higher at faster speeds. I would think that any increased engine heat would be offset by the increased airflow through the radiator. (Which is new, by the way.)

Two questions:

1. Is this normal? Are these temps what you guys see?

2. Is there anything I can do to reduce the temperature?

I've read in some posts that the air dam/spoiler under the nose is there to force air up into the radiator at higher speeds. Would adding some sort of baffling to that air dam help?

Thanks!

427Hotrod

Having all the flaps and seals around the radiator helps a lot. Since it's angled it's easy for air to go over it instead of through it at speed.

My gut tells me it's just a capacity issue...meaning that radiator can't get rid of the heat. Either plugged some, scale internally coating tubes etc. Could be a hose collapsing, could be a T-stat not allowing enough flow.

I used to participate in some high speed spirited runs around the Houston Beltway on Sunday mornings with a bunch of other Vette folks. They were C-4's/C-5's and I was the only one without an O/D. Mine would creep up on heat. I finally removed the t-stat and the issue went away. Haven't run one since. It gets to temp fine without it. Mine just has a stock radiator, shroud and fixed blade fan with stock pulleys. Not saying you should remove it, but I'd make sure it was opening enough....there are hi-flow styles.

JIM

Metalhead140

Do you have the foam seals between the radiator and radiator support in place? And you do definitely have the spoiler under the nose? Mine did this when I bought it too, but I chucked in a new alloy radiator when I rebuilt the engine, and never had an issue since. You say you have a new radiator though...?

AboveTheLogic

Is your chin spoiler missing or damaged? I had the same symptoms on my '79- hot only on the highway, when the chin spoiler was off the car. I removed it because it was all busted up. Put it back on, even busted up, and it drastically helped with the temps.

There is an extended front spoiler available too, helps even more.

jjhoneck

Not sure about the foam seals -- I will check that tomorrow.

The radiator was replaced by the previous owner in 2014-15. It's alloy and looks brand new.

The little spoiler is under the nose.

jjhoneck

Yep, the little spoiler is under the nose. Might have to look into that extended model?

AboveTheLogic

I'm guessing you don't have an overdrive transmission and the engine is spinning well over 3,000rpm when you experience the rise in temps.

Is your lower radiator hose collapsing under higher RPM? Does it have the spring inside, or could there be air in the system?

At 80mph, when the temp climbs, if you put it in neutral or hold the clutch in and coast for a few seconds, does the temperature drop? If so, that symptom is indicative of a collapsing hose where when you let the RPMs drop the water pump doesn't suck as much out of the lower hose, allowing it to open up and the cooler coolant from the radiator to make it through the engine.

As a quick test, watch the hose and rev the engine and see what it does.

jb78L-82

The hotter temps on C3's especially on the later C3's is a very common issue. The suggestion about the foam seals is a good one and the collapsing lower hose maybe, but I doubt it. The 45 degree radiator position along with the restricted air flow into the nose are an issue as well the smog cylinder heads causing the engine to run hot.

I solved this issue years ago and can now run my rebuilt 425+ Gross HP L-82 all day long at 3,500 rpm on the highway with 3.70 gears and 4 speed and the temp never budges off the 180 mark on the gauge.

I have the following:

The spoiler extension from the 79 C3's with heavy duty cooling (see picture below)-on the car since 1990
Dewitts aluminum radiator-mid 2000's installed
Stewart aluminum Stage 2 high flow water pump-mid 2000's installed
Robertshaw modified 180 degree thermostat
OEM original heavy duty L-82 fan and fan clutch-GM installed




BTW- My foam radiator seals are all original and NOT in the best of shape but the cooling system has so much excess capacity now, the highway temps are never an issue regardless of the ambient temp outside....

jjhoneck

Thanks for the info. What is meant by a "smog cylinder head".

Any idea on where one can buy that extended spoiler?

jjhoneck

Thanks for the ideas. I will check that lower hose today.

TimAT

I solved mine by removing the front license plate and bracket.

jjhoneck

I did that, too. No change.

Temps are still in the green, but I'd sure rather see them in the 180 degree range.

BKarol

Willcox lists it on their site:

https://willcoxcorvette.com/catalogs...iler+extension

I put one on my 78 because the temp would read over 200 on the highway. Ever since the install years ago my temp never has gone over 200. But that is me.

Attaches like this & unsure how it attaches on your year. Perhaps Willcox can let you know.:

ajrothm

Definitely a water restriction of some sort.... Either the radiator is not that good, the suction hose doesnt have a spring and is collapsing at high rpms or the thermostat is too restrictive. Also, if your water pump is worn out internally (too much impeller to volute clearance) can cause cavitation at high rpms.

Its definitely not normal to run HOTTER at freeway speeds.. You should easily stay under 200* at 70-80 mph...

Rescue Rogers

Mine did the same thing and I took out the 190 thermostat and put in a 180. Now at 80mph it stays around 185-195 I would guess. Definitely below the 200 marker

BLUE1972

Check your timing to be sure the timing is set properly. Use 93 octane gas.

Most of todays thermostats are junk and fail within a year or so. I would get an AMERICIAN made 180 and swap it. Use a GM gasket with the silicone ring to prevent leaks - a cheap swap.

I would check the lower hose for a spring, if it's missing replace the hose. You can rev the engine and see if the hose collapses. Squeeze the hose and see if it collapses.

I agree that if the water pump impeller is worn it will have cavitation and cause a hot condition.

If the radiator seals are missing this can cause a hot condition also.

A partially clogged radiator will also cause the issue - this is a remove and have it tested and boiled at a good shop.

jb78L-82

As Karol states, Willcox has the spoiler reproduction. I bought mine for my 78 L-82 in the very late 80's from a local Chevy dealer after seeing that spoiler on a 79 L-82 at a car show.

The mid to late 70's C3's have "882" cylinder heads designed to run VERY hot for emissions reasons and the reason that they almost always eventually crack.

The late 70's C3's especially 78-80 L-82 (NOT the base engine L-48's)are notorious for running hot on the HIGHWAY. My 78 L-82 ran 235-245 routinely on the highway with the AC on at 65-70 MPH. My buddy's 79 L-82 4 speed like mine also bought new ran the same temperatures. The temperature issue was a common problem for the L-82's in the late 70's.

My engine temp issue had nothing to do with the radiator hose collapsing and your issue does not sound like that solution either. A new aluminum radiator, high flow water pump, and Robertshaw thermostat most probably will solve the issue assuming you have checked some of the easier fixes like timing, foam seals, carb running too lean, etc.

cv67

Simple stuff like blasting out the radiator fins wtih a water hose once a yr can help youd be surprised what comes out thats lodged in there.

maj75

Especially if you have an AC condenser in front of the radiator. Common problem, even in later model Corvettes. I bought a tool which connects to an air hose and you can slip it between the radiator and the condenser and blow the dirt out the front of the radiator and condenser.

dmruschell

My 425+hp rebuilt L48 in my 79 used to get a bit over 220 on the highway with the A/C on, even with a DeWitts radiator. The front spoiler extension solved that problem. I haven't had any engine overheating issues since I put it on.

I attached mine using nuts and bolts.