Thread: Delayed overheating problem

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Background info:

1980 Camaro Z/28

Rebuilt 350, slightly bigger cam, holley 600 carb, edelbrock intake manifold, hedman headers and exhaust.

Overheated really bad transporting it halfway across the country around 2 years ago, fixed it after an hour of driving by replacing the flex fan with a bigger one (15" to 17") that fit the shroud much better. Fan is inside the shroud at most a quarter inch, and that's with a 4 inch spacer.

Problem:

Once I start it up to drive somewhere, the engine climbs in temperature normally, but then goes past the middle ideal mark (210) and keeps climbing until it's right on the edge of the redline. At which point I try to let off the gas as much as safely possible to help the temperature decrease. It stays borderline red for about 40 seconds and then creeps back down to 210 and stays there. My first assumption was that it sounded like a slow thermostat (if that's even possible), but I replaced the thermostat about 2 years ago. My current plan is to switch to an electric fan setup, with the benefits of better cooling and I assume less load on the engine due to the better efficiency of the electric motor? But first I wanted to run it by you guys to see if you had any insight. Thanks!

My first reaction is that you used a cheap poppet style thermostat.. if you did, replace it with a sleeve type. The sleeve type will flow more and maintain an even temperature.

I'd also try to get the fan into the shroud opening more. either add more spacer or add to the shroud??

Originally Posted by 34_40

My first reaction is that you used a cheap poppet style thermostat.. if you did, replace it with a sleeve type. The sleeve type will flow more and maintain an even temperature.

I'd also try to get the fan into the shroud opening more. either add more spacer or add to the shroud??

I'm tracking with Mike. My first thought was a sticking thermostat, hanging closed until the higher than desired temp can generate enough force to clear the interference. Also, like Mike says, the fan needs to be into the shroud at least 1/2 way, and ideally with only about 1/4" to 1/2" of blade on the outside of the shroud opening, and OD clearing the shroud opening not more than ~1/2", depth being just as important as "fit", IMO.

There are a lot of people that agree with your assumption that an electric fan is going to be more efficient than your mechanical, but I do not agree. With an aftermarket electric you will have more restriction at speed than a well fit shroud & fan, and while it doesn't seem logical the amount of electrical "work" required will load the engine just as much as the mechanical, and the mechanical fan will actually "coast" when the clutch disengages at temperature while the electric may still be energized. Your increased alternator load will require as much, or more power than your current fan. My advice is stick with the mechanical fan, replace the thermostat first, and then if that doesn't fix it look at the fan/shroud clearances.

Just a couple of thoughts.

The first is are you SURE it’s overheating. I have found some gauges, especially factory electric gauges on older vehicles to be very inaccurate. Factory tolerances, wiring and grounds that have degraded over the years and replacement sending units can all factor in to this.

A few years ago I spent a huge amount of hours and fair amount of $ changing fans and putting in a new radiator in a car only to find out the car was really only running at 190-200 degrees. Another one was my DD 84 El Camino that has a factory gauge cluster and the temp gauge in that reads a constant 30 degrees hotter than the actual temperature is. After changing the sender a couple of times and not being able to find a replacement gauge, I've just gotten used to it. I have found that a temperature gun is a great tool to have to start the diagnosis process before spending a dime on hardware (it's a lot cheaper than buying a new radiator you don't need).

The second thought I have is that what you are describing sounds like at speed the blades of the flex fan are flattening out and not drawing enough air thru the radiator at speed (as you slow down the blades curve more and start drawing the needed air). Just from my experience (other may vary), aftermarket flex fans often have blades that flatten out too quickly. Personally I prefer to use Ford 6 or 7 blade flex fans if I have to use a flex fan....... and for gods sake don't get hung up on the little oval marking that indicates who made the fan over keeping the engine cool.

Personally I prefer a mechanical 7 blade fan with a HD clutch (the thick one speced for BB Chevy trucks) over electric fans. The fan locks up at 210 degrees and with the factory 7 blade fan and shroud I doubt you have any more heating problems.

My problem with using electric fans is that generally speaking the cheap ones really don't pull sufficient air, and the better ones can put a pretty good strain on an older electrical system.

Anyway, that's my 2 cents.


.

Personal experience says: have the radiator serviced.

It's fairly common, the radiator is a little plugged up, and cooled the motor fine, but then you went and rebuilt the motor, and it now makes more power, and more HEAT.

If you're having cooling issues at highway speed you have more than a fan problem. As mentioned I would have the radiator re-cored and back flush the block and use a good quality thermostat along with the proper fan placed in the shroud. Also where is the timing set? If you're running mechanical advance are the counter weights free and not sticking? It's possible to drive a car at highway speeds with no fan, been there, done that.

First off, thanks for the replies everyone! You guys are extremely helpful.

Originally Posted by 34_40

My first reaction is that you used a cheap poppet style thermostat.. if you did, replace it with a sleeve type. The sleeve type will flow more and maintain an even temperature.

I'd also try to get the fan into the shroud opening more. either add more spacer or add to the shroud??

Originally Posted by rspears

I'm tracking with Mike. My first thought was a sticking thermostat, hanging closed until the higher than desired temp can generate enough force to clear the interference. Also, like Mike says, the fan needs to be into the shroud at least 1/2 way, and ideally with only about 1/4" to 1/2" of blade on the outside of the shroud opening, and OD clearing the shroud opening not more than ~1/2", depth being just as important as "fit", IMO.

There are a lot of people that agree with your assumption that an electric fan is going to be more efficient than your mechanical, but I do not agree. With an aftermarket electric you will have more restriction at speed than a well fit shroud & fan, and while it doesn't seem logical the amount of electrical "work" required will load the engine just as much as the mechanical, and the mechanical fan will actually "coast" when the clutch disengages at temperature while the electric may still be energized. Your increased alternator load will require as much, or more power than your current fan. My advice is stick with the mechanical fan, replace the thermostat first, and then if that doesn't fix it look at the fan/shroud clearances.

Originally Posted by Mike P

Just a couple of thoughts.

The first is are you SURE it’s overheating. I have found some gauges, especially factory electric gauges on older vehicles to be very inaccurate. Factory tolerances, wiring and grounds that have degraded over the years and replacement sending units can all factor in to this.

A few years ago I spent a huge amount of hours and fair amount of $ changing fans and putting in a new radiator in a car only to find out the car was really only running at 190-200 degrees. Another one was my DD 84 El Camino that has a factory gauge cluster and the temp gauge in that reads a constant 30 degrees hotter than the actual temperature is. After changing the sender a couple of times and not being able to find a replacement gauge, I've just gotten used to it. I have found that a temperature gun is a great tool to have to start the diagnosis process before spending a dime on hardware (it's a lot cheaper than buying a new radiator you don't need).

The second thought I have is that what you are describing sounds like at speed the blades of the flex fan are flattening out and not drawing enough air thru the radiator at speed (as you slow down the blades curve more and start drawing the needed air). Just from my experience (other may vary), aftermarket flex fans often have blades that flatten out too quickly. Personally I prefer to use Ford 6 or 7 blade flex fans if I have to use a flex fan....... and for gods sake don't get hung up on the little oval marking that indicates who made the fan over keeping the engine cool.

Personally I prefer a mechanical 7 blade fan with a HD clutch (the thick one speced for BB Chevy trucks) over electric fans. The fan locks up at 210 degrees and with the factory 7 blade fan and shroud I doubt you have any more heating problems.

My problem with using electric fans is that generally speaking the cheap ones really don't pull sufficient air, and the better ones can put a pretty good strain on an older electrical system.

Anyway, that's my 2 cents.


.

Originally Posted by firebird77clone

Personal experience says: have the radiator serviced.

It's fairly common, the radiator is a little plugged up, and cooled the motor fine, but then you went and rebuilt the motor, and it now makes more power, and more HEAT.

Originally Posted by NTFDAY

If you're having cooling issues at highway speed you have more than a fan problem. As mentioned I would have the radiator re-cored and back flush the block and use a good quality thermostat along with the proper fan placed in the shroud. Also where is the timing set? If you're running mechanical advance are the counter weights free and not sticking? It's possible to drive a car at highway speeds with no fan, been there, done that.

Story time (replies to everyone below): I rebuilt it with my dad in Oklahoma, then had to drive my black car with black interior from Oklahoma to California (for college) in the middle of August. 30 minutes after driving it was overheating, and I had the heater on to try and help. I've never been in such a hot car my whole life. So I pulled off at a highway gas station (no town nearby) with the idea to remove the thermostat to increase the flow, but it didn't help. 30 minutes later (and driving ~45 mph on a 75 mph highway) I come to the nearest town.

Found a Pep Boys and went inside to try to figure something out. I had a lot of tools with me so I was considering all options. For a while I was going to install an electric fan. Pep Boys shop technicians came out to look at the car. One guy squeezed my radiator hose and tried to tell me that there was way too much pressure and I probably had a cracked head. He also told me I should leave it overnight so they could work on it in the morning (this was around 8 pm). Side note: he was an idiot/scammer right? The pressure in that hose is reliant on the pressure release valve in the radiator cap isn't it?

Anyways, I had less than an hour to figure something out before the shop closed and was starting to freak out a little. I bought another 2 inch spacer to get the fan further in the shroud but they didn't have long enough bolts. Spent nearly half an hour fiddling with the too short bolts thinking I could get enough bite with them. Then I asked what kind of mechanical fans they had, with the idea that mine was flexing too much. Then it dawned on me when they told me the sizes, I would just get a bigger diameter fan. I went from a 15" to a 17". The 17" barely fit, in fact it was so tight that it took a tiny bit of plastic off when I first started it up, but after a couple seconds it took off enough that it wasn't rubbing and was a perfect fit. Which worked very well at fixing the overheating problem. So I put the thermostat back in (fortunately the gasket was so new that it survived, Pep Boys was closed at this point) and continued the trip.

Spent the night at a friends house and set off at 3 in the morning because the temperature was still cool. Car was running well, I wasn't drenched in sweat, things were looking good. Then the sun starts to rise and it slowly gets hot again. Cooling by open windows just wasn't enough (it's ~102 degrees outside and again, black exterior/interior) so I am stoked about finally getting to use the a/c I paid a hose shop a crazy amount to replace the high pressure hose. I turn it on and hear squealing and immediately turn it off. So I pull off at a gas station and have my girlfriend turn on the a/c while I watch it and the belt is jumping on the pulling. So I assume my compressor had seized up after not being used for around ten years. Awesome.

So I then had to drive 2000 miles in this boiling hot car. We had towels with us, so at one point we laid them on our seat and the floor and started getting bags of ice at gas stations just to rub them on our skin, it was that hot. My left arm got sunburned so bad, it's actually pretty hilarious now that I can look back on it. Here's a picture of the car on the final stretch of the road trip from hell:





Despite the heat and car problems, it was actually pretty fun.

Back to the task at hand

34_40:
Is this the bobbet style?



If so then that's what I have and I'll go grab a sleeve thermostat. Funnily enough, when I first started the engine it was overheating really badly. So I replaced the thermostat, but it still was overheating. So I grabbed the thermostat and stuck it in a pot of boiling water to make sure it was actually opening. Was really cool to watch, and it did indeed work. Installed the 4 inch spacer on the fan and it cooled much better just idling in my driveway so I left it at that.I will definitely try to get the fan in the shroud more, I think I still have that 2" spacer around here somewhere, I'll go get longer bolts today.


rspears:
I appreciate the guidelines for the fan dimensions, I'll make sure to get it within those tolerances. I also appreciate the advice on the electric fan, you just saved me a lot of time and money. That was also an interesting read, I guess another benefit of the mechanical fan is reliability (if it's set up correctly haha).


Mike P:
You very well could be on to something, the gauge is stock so it could be faulty. My reason for thinking it is overheating is that it goes to the redline, then slowly goes back down to the middle line (210) and stays there for the rest of the trip. That's also a good point about the flex fan, it was a pretty cheap fan and could very well be doing that. The blades flex out when at higher rpms because there is more air moving over the radiator right? What never made sense to me was that if this concept is aimed at cooling the radiator at more efficient rates, doesn't it "reset" when you change gears and the rpms drop? I have the old fan sitting in my parents garage in Oklahoma, I'll look into the cost of getting it up here.


firebird77clone:
I actually had to replace the radiator during the rebuild because the old one had a horrible leak in it. Before I rebuilt the engine I had the block cleaned in a vat at a shop so hopefully there was nothing in the system, but anything is possible, especially with my luck. Can I do a flush/service myself?


NTFDAY:
Timing is a bit of an issue right now, actually a pretty big issue. The engine I have I got from a scrapyard (2 bolt main 350 originally from a 1972 Chevelle, at least that's what they told me) and didn't come with the bracket for doing timing adjustment (you use a timing light to compare the harmonic balancer with the bracket right?). Although I did buy a timing light. So to adjust it I just turned the distributor one way until the engine stumbled, then turned it the other way until it stumbled and set it at the middle ground. I did the same thing with the air/fuel mixture screw on the carb. However, these are two separate variables that effect each other, so I feel like using this method on both is really difficult to get everything right. It almost seems like a system of linear equations.

Check the counter weights under the module in the dist and make sure they move freely. If you have a vacuum gauge you can get the timing fairly close, adjust for the highest reading and back it off just a tad and you'll be in the ball park and you can do the same with the air/fuel mixture screws on the carb except you adjust for the highest steady reading. Old radiator hoses do have a tendency to collapse under pressure and heat and will restrict water flow.

Originally Posted by NTFDAY

Old radiator hoses do have a tendency to collapse under pressure and heat and will restrict water flow.

Along the lines of checking the simple things first, you do have a spring inside the lower radiator hose, right? If not you could be sucking that hose closed as rpm's increase, severely reducing your flow. And when you say you had to get another radiator, that was a new/rebuilt unit and not one from the salvage yard, right?

Originally Posted by NTFDAY

Check the counter weights under the module in the dist and make sure they move freely. If you have a vacuum gauge you can get the timing fairly close, adjust for the highest reading and back it off just a tad and you'll be in the ball park and you can do the same with the air/fuel mixture screws on the carb except you adjust for the highest steady reading. Old radiator hoses do have a tendency to collapse under pressure and heat and will restrict water flow.

I actually do have a vac gauge, will try that right now. I appreciate it! And after testing the hoses by pinching them I think you're definitely on to something.

Originally Posted by rspears

Along the lines of checking the simple things first, you do have a spring inside the lower radiator hose, right? If not you could be sucking that hose closed as rpm's increase, severely reducing your flow. And when you say you had to get another radiator, that was a new/rebuilt unit and not one from the salvage yard, right?

Interesting, I just went in the garage to try squeezing the lower hose and it compressed way easier than I was expecting. Also way easier than when I first installed the hoses, which could explain why I never used to have this initial overheating problem after I initially fixed the problem with a bigger fan. The upper hose was a lot weaker as well. Although I don't have to worry about the upper hose because it has positive pressure and the lower hose has negative pressure right? Also would O'Reillys have the springs I need for the lower hose? And I replaced the radiator with a brand new one.


As a side note, after a 10-15 minute drive the starter really struggles to turn it over. I replaced the starter just last week with one of those cheap ebay "3 hp" electric starters from DB electrical (I was hesitant at first but read good reviews about it), because the old starter I was using had stopped working. When cold, or mildly warm, it starts beautifully, much faster than the old starter. But just yesterday I was driving home from the grocery store and pulled into the driveway. Got out to open the garage door, then started it back up to drive in and it really struggled to turn it over.

A lot of times hard staring issues when hot can be caused by a number of things, too small positive battery cable 8gauge, IMHO, is borderline 6gauge and bigger is better. Rule of thumb, the further the battery is from the starter the larger gauge the cable needs to be. A poorly grounded neg cable will also create your problem as will a weak battery. Also ignition timing too far advanced.

Bit of an update:

Just tried revving it with the hood open and watching the lower radiator hose, it doesn't really seem to collapse, but maybe that's because it wasn't fully warmed up yet. Will get it warmed up while adjusting the carb/timing and try again. Here's some pics of the fan inside the shroud, now that I look at it I could definitely use some more depth.

WARNING.. those starters from China are not a good thing your better off getting an OEM starter. I have changed out those high tork starter made I china as they have a plastic arm inside to bring the gear in and they open up and quit working. They won't last under hard starting.

Originally Posted by NTFDAY

A lot of times hard staring issues when hot can be caused by a number of things, too small positive battery cable 8gauge, IMHO, is borderline 6gauge and bigger is better. Rule of thumb, the further the battery is from the starter the larger gauge the cable needs to be. A poorly grounded neg cable will also create your problem as will a weak battery. Also ignition timing too far advanced.

Not sure what size the cable is but it's pretty large, will go see if I can find any markings on it. Both the cable and the battery were replaced around 2-3 years ago. A little elaboration on the hard starting problem, it barely turns over when very warm, maybe once a second for the first 4 revolutions, then it picks up speed. And eventually fires.