75 cooling question

[Dave C]

I have just purchased a 1975 coupe this car has been completly rebuilt however I have a concern with the way the coolant gauge goes. When I am driving down the road at 110kmh/ 70 mph the gauge goes very close to the hot area about a needle width from it. in town and in heavy traffic the car runs at 200. There is a new waterpump and 180 degree thermostat in the car. Is this normal for a car of this year?

 

[Trixie]

On the freeway or in town, mine sits at about 200. I am constantly watching the guage because I don't want to push the ol horse beyond her limits.

 

[wolf_walker]

Same here on the 74, and it's currently in pieces awaiting a new radiator, water pump and t-stat, and a good flushing. It never broke 210 or so, but that strikes me as a little much for a stock 350 chevy.

 

[Dave L.]

My 81 runs 180-190 even on the hotest days.I have 107000 miles on the original engine.The radiator has been recond. and all the hoses replaced including a new water pump. I have never seen my guage hit 200.

 

[MoeJr]

The 68-82's were known for bein tough to keep cool. I know on the later 81 and 82 they used aux electric fans and mid to late 70's L82's also had these fans so I have been told. I would believe you may need a hi flow water pump and t-stat to gte better cooling along with a full cooling system flush. 220 is not uncommon on 75's as the mid 70's Vettes used cats which allowed the engineers to run the cars dirtier and hotter to try and recoup some of the lost horsepower from the emmissions stuff. Hope this helps.

 

[78SilvAnniv]

Major cooling issues got me hot!

The 78 had a chronic problem with running too hot during hot weather.

We replaced the radiator and installed new hoses.
We replaced the clutch fan several times.
We tried different temp t-stats.
We replaced the water pump.
We even installed a new crate engine.

After all this, if I used the AC, temp shot up to 240, no matter if I was in town or on the hwy! So much $ to fix the AC and I dared not use it.

This past summer, I had Kenny install a high quality flex fan, and it has solved my run-hot problems. I can now drive faster than 55 in the summer AND run my AC in town or on the hwy.

There has been some discussion as to whether a flex fan is the best option, but it worked for me and solved my problems.
Heidi

 

[rpounds]

My '75 runs thermostat temperature. I normally run a 180 degree until California smog check time. Then I change it out to a 195 just long enough to get it checked and then it's back to the 180. Regardless of which I have in there, it runs right at thermostat temperature. However, it wasn't always that way. When I purchased the car, it ran hot, especially at freeway speeds. It would creep up and up and up, until it got a little scary.

The difference? A new radiator and replacement of all of the seals that surround the radiator. It is imperative that all of the air flow be focused into the radiator. That means that all of the original equipment be in place and in good working order, including the clutch fan, air dam, seals around the radiator, hood to radiator frame rubber, etc. If the radiator is original to the car, it has without a doubt lost it's efficiency over the years.

I really struggled with having to pop for a new radiator, even though I knew in my heart that the radiator was the culprit in my cooling problems. Even with the preponderance of evidence, it took another engineer (John Z of this board) to convince me to buy a new one. I tried water wetter, examined the water pump, checked and rechecked the timing, etc. What it needed was a new radiator with all of the seals in place.

I know that I have gone on and on about this, but cooling problems come up on this board over and over and over. Unless pieces and parts, such as the air dam under the nose, have been taken off, it is more than likely a radiator that has outlived it's usefulness.

Just my $.02. Sorry for the long post.

Hey! Us '75 people gotta stick together!!

 

[Ala75Vette]

My '75 reaches operating temp at about 200 and stays there unless I'm really pushing it (cruising at 80 or so on the interstate), but even then it never goes over about 210 or so.

 

[wicky88s1975]

My 75 runs at 180 all the time hard or easy. (by the way rpounds, the newer tvs' on my 350 operate at 165, so you shouldn't have a problem with the Smog nazis) The Block is newer by 2 years with upgrades from a 1980 donor(al intake and exhaust manifolds). I would agree with whays been said though, if air flow to the radiator is good then it must be the radiator.

 

[c4ever]

Dave,
I wouldn't neccesarily trust the guage. My 82 guage is off by 10+ degrees. Do an actual temp test. What is curious is that you run hotter temps cruisin than you do sitting in traffic:confused

I run, even with the heat in S. FL, 190 cruisin and 200-210 traffic (with A/C on or off)
New radiator (stock-OEM) new water pump (Delco) 160 stat.

 

[Bob Chadwick]

I agree with C4Ever. On a 90+ day in Atlanta I run right around and under 200 at any constant speed from 25mph to highway speed. If I get in stop and go traffic it can get up around 210.

It's interesting that yours runs the other way around. Perhaps this is a shroud/air direction issue in that at higher speed the high speed air flow is not being directed over the radiator by the movement of the car and at lower speeds it is relying more on the fan and not being impacted by the car movement.

Bob

 

[rpounds]

On a 90+ day in Atlanta I run right around and under 200 at any constant speed from 25mph to highway speed. If I get in stop and go traffic it can get up around 210. It's interesting that yours runs the other way around.

This is exactly the way my '75 reacted. The factory set up was still in place. I pulled my hair out over this for a while (and I don't have that much hair left to pull) . But, it does make sense. When you are driving faster, you are using more throttle, making and using more power, putting more of a strain on the engine - and you are generating more heat. The radiator has to deal with that extra heat. If it has lost some of it's efficiency, then it will not be able to deal with the extra heat.

The good news is, if it cools down in traffic as mine did, then your clutch fan is working well

By the way, Wicky what color are the TVS' in your car? I know that's a strange question, but the general color coded them for us.

 

[Bob Chadwick]

When you are driving faster, you are using more throttle, making and using more power, putting more of a strain on the engine - and you are generating more heat. The radiator has to deal with that extra heat. If it has lost some of it's efficiency, then it will not be able to deal with the extra heat.

Fortunately the radiator gets the added help of more air flow generated by the movement of the car to help deal with this added heat. I'm not particularly concerned about temperatures under 210 or so.

The problem with these old cooling setups is the mechanical fan. When the car is not moving and is idling slowly, the fan is moving slow and does not necessarily move enough air on a hot day to cool the car. That is why they went with electric fans, which generate the right air flow using a thermostatically controlled electric motor at a wide range of variable.

Flex fans were a go for a while, generating more air flow at slower speeds due to the increased pitch of the blade at slow revolutions. At high speeds they flattened out and used the movement of the car to assist with air flow, though they had a propensity to actually block air flow as they flattened and reduced the space between the blades.

 

[wicky88s1975]

rpounds, Tvs for efe is green and mounted on the thero housing and the egr is blue on the intake manifold

 

[rpounds]

Thanks Wicky. I'll have to check out the local FLAPS to see if they have the right ones . . .