I inherited a '70 Cutlass Supreme convertible that was cloned to a 442 with the engine changed to a 455. I know almost nothing about the car, other than the work I have had done on it. I am sure I will have other questions come up as I try to answer potential buyer's questions but my current question is this: What is a normal amount of idling/ slow driving that can be expected from this car before it overheats (water temp gauge reads 200+ degrees) I am taking it to the mechanic next week, they said they had some cheap fixes they can try. I need to know if it is fixed 'good enough' that I don't have to disclose an over heating problem, which is apparently a deal breaker for potential buyers.
It is an automatic, and has no ac compressor.

 

Welcome to the site. I moved your post to its own thread. 200+ degrees is not overheating during extended idling or in traffic, need a bit more info on your issue. What is the scenario in which the temp is climbing? What distributor and carb? What are your tuneup settings, dwell, timing, plug gaps...? What type of fan and size of radiator?

 

I do not know the answer to any of your technical questions, what I am trying to learn is, what is the maximum temperature the water gauge should reach before you say "yikes" and pull over to let the car cool? And how would you gauge that a car with a 455 engine is cooling normally, or over heating too easily? I am thinking that x number of minutes driving in stop and go traffic or idling in the driveway without excess heat means it is ok. I realize there are threads with all the technical fixes for overheating, but I have to leave that to my mechanic. I just need to know if he has solved the problem, or if we should try the next step. I have been told that the big engines get hot, and that is to be expected- but how hot is hot, and when is it expected and when is it overheating?

 

GM's engines were specced to do 250. A 50/50 antifreeze mix at 14 psig will boil at @260. 250 is the highest you want to see on a functional gauge, and you would only want it to ever spike that high briefly. Overheating is a misused term. It means "boiling over" which results in boiling coolant busting out of somewhere, usually the overflow. Running warm, or running hot, is more accurate. These cars came from the factory with 190 or so thermostats, which meant they were meant to run there.

Ideally, the thermostat should regulate the temp, and it should be able to pull the temp of the car back down to it no matter what. However, big engines need big radiators, and old radiators get gunked. Perhaps the cloned car has the original radiator. However, 200 degrees in traffic and idling is not overheating, and while not optimal, is not bad.

First thing that needs to occur is accurate verification of the gauge.

 

I guess the yikes number is start worrying about the 235 mark and pull over at 240, the Temp lights come on at around 245-250. At 260 bad things start to happen.

 

Thanks! I have no functioning temp lights, the temp gauge is a newer add-on. I haven't had it boil over, just get hot. Dad told me what temp to watch for, but I couldn't remember what he said. So now I know what to look for, I'll get back to you if I am still having problems after the mechanic adds a thermostat and checks the radiator cap and coolant. I am hoping it isn't the radiator, I don't want to put lots more money in it.

 

Well, I can tell you that flex fans (which I see in your picture) are notorious for not pulling sufficient air across the radiator, which can lead to running warmer. A factory fan setup will work much better.

Another thing to consider is the ambient temperature. If your engine is running 190-200 on a hot (90º) summer day that is totally different than running the same temp on a cold winter day.

 

An engine temperature of 210F is perfectly acceptable and nothing to be concerned about. People on this site have this overarching paranoia about any temperature that hits the 200F mark like that's a disaster. It's anything but.

A 190 degree thermostat does not mean that the engine should operate at 190F and no more. That's just the temperature at which the thermostat opens to let coolant begin flowing through the radiator. The engine's temperature can exceed this in normal operation.

Remember, in the good old days, we didn't have gauges. We just had idiot lights, and we didn't worry about the engine temperature until and unless the light went on. For all we knew, the engine was running at 225F and never had any problem. Now, with gauges, we have too much information.

If I were you, absent any other signs of overheating, I would take a deep breath, sit down, and recognize that your engine is very likely perfectly normal. Just drive the car and enjoy it.

 

You're selling the car and you have no mechanical skills or knowledge, so what do you care anyway?

That being said, your fan is crap.
It's a flex fan, which won't move air well, is noisy, and will rob you of both top end power and MPG.
It's also much too small for your fan shroud, so it can't pull air through when you're stopped or moving slowly, which will cause exactly the problems you describe.

If you want the car to run cool at idle or in traffic, you need to get an OEM 7-blade fan with a good quality heavy duty fan clutch. There are a number of members here who should have a fan lying around to sell.

It's hard to tell, but you're radiator appears to be an aftermarket hot-rod aluminum radiator, which should be more efficient than GM's original radiator, all other things being equal. I don't know enough about specific aftermarket radiators to comment in greater detail, but another member may be able to identify the specific make and model and offer an opinion on its quality.

Welcome to ClassicOlds.

- Eric

 

You can advertise that car on this site for free. Go to the cars for sale Forum, Post pictures and info. Lot of members here may be interested. Good luck with the sale.

 

So, of course since I am trying to sell the car, the switch for the power top goes out. The mechanic said he tried cleaning it up, but that didn't work and so he is looking online for one. Can you recommend a good sourcef?

 

I have a nice 7 blade fan if you find you need one.
Welcome aboard.

Johnny

 

Thanks Johnny, I think I am done with fixes. I'll let whoever buys the car know, though.

 

My mechanic put in a thermostat and fixed the radiator cap and added coolant. They drove it for a long time, I drove it for a long time (around the local mall with for sale signs on) and it only got up to 240 once. I took it out to a bigger street where I could run it at 50 mph and it cooled right down. Now that I know what temps to worry about, I feel much better about it getting hot. Your advice is greatly appreciated!

 

I think that indicates the fan is not pulling enough air across the radiator at low speeds, which is what I would expect from a flex fan.

 

It looks to me like the shroud is 'installed' upside down. I use the term 'installed' loosely, because it appears to be fastened to the radiator with zip ties.

I believe this car would originally have had a six-blade, 19" diameter fan. That flex fan looks to be 5-blades and maybe 16" diameter. With that and the shroud installed wrong, it's practically useless. The shroud may actually be doing more harm than good in this case.

I would not consider 240 degrees acceptable. At idle even on a very warm day the factory setup should keep you between 190 and 215 degrees.

 

You are correct about the shroud - the lower mounting tabs are at the top in that picture.

 

LOL! this car has obviously been owned by "experts" Thanks for pointing these things out.