???Coolant Temperature Sending Unit???

[Beach-Burban]

Originally Posted by BAD1916

My 71 Suburban with a 454 runs right around 190ish almost always while driving. It will hit 220 in bumper To bumper traffic and will creep up to 210 at stoplights but cools down quick once I start moving again.

It may be that this is where 454's normally run? This is only my second BBC...the first was a built 402 out of a '72 truck that I installed in my '65 GTO (when I was 18...and I'm 65 now!) but I never had any cooling issues with that car, even when towing my sand rail with it (in the desert heat!).

Woody

[FLYNAVY30]

I've been doing a lot of research on this exact topic, as I needed to replace the water pump on my Corvette. I found an excellent article written by one of the NCRS guys about how cooling systems work, and how to troubleshoot overheating issues (as they are common in early Corvettes). A few of my lessons learned:

1. Pusher fans are a band aid solution for something else wrong with the cooling system

2. Ignition timing, especially with vacuum advance has more to do with cooling than I ever imagined

3. Thermostat temp setting has nothing to do with the maximum cooling ability of the system, or what your temperature will rise to in a given situation.

If you shoot me an email (GPaules03@gmail.com), I can send you the full .pdf article. It is specific to the cooling system in the early Corvettes, but 95% of it applies to any old cooling system.

[Beach-Burban]

Originally Posted by FLYNAVY30

I've been doing a lot of research on this exact topic, as I needed to replace the water pump on my Corvette. I found an excellent article written by one of the NCRS guys about how cooling systems work, and how to troubleshoot overheating issues (as they are common in early Corvettes). A few of my lessons learned:

1. Pusher fans are a band aid solution for something else wrong with the cooling system

2. Ignition timing, especially with vacuum advance has more to do with cooling than I ever imagined

3. Thermostat temp setting has nothing to do with the maximum cooling ability of the system, or what your temperature will rise to in a given situation.

If you shoot me an email (GPaules03@gmail.com), I can send you the full .pdf article. It is specific to the cooling system in the early Corvettes, but 95% of it applies to any old cooling system.

Thanks Greg...E-mail is on the way!

Woody

[HO455]

No need to apologize for posting lots of information on a problem. You have done a great job troubleshooting this problem.
A couple of thoughts. I am guessing that the motor has a fair amount of miles on it from your report on how dirty the water was. Tired engines can run hot.
I had overheating problems on an old 236 Chevrolet 6 that was cured by removing the water pump and physically rodding the rusty clay that had collected in the bottom third of the water passages around the cylinders. You may have a similar situation. However it's nowhere as easy to access the passages on a BBC as it is on a 235.
And as FlyNavy says ignition timing can be a big factor. Do you have access to a distributor machine?
Have you tried disconnecting and plugging the vacuum advance hose to the distributor to see if that helps?
Pusher fans are really more of an air flow reducer and should not be used unless there is on option for a puller fan.
And it is hard to tell from the photos, how much of the fan blade sticks out past the rear edge of the shroud? You should have about 1/3 of the fan blade past the back edge of the shroud. This link may help.

http://67-72chevytrucks.com/vboard/s...d.php?t=582331

[Beach-Burban]

Originally Posted by HO455

No need to apologize for posting lots of information on a problem. You have done a great job troubleshooting this problem.
A couple of thoughts. I am guessing that the motor has a fair amount of miles on it from your report on how dirty the water was. Tired engines can run hot.
I had overheating problems on an old 236 Chevrolet 6 that was cured by removing the water pump and physically rodding the rusty clay that had collected in the bottom third of the water passages around the cylinders. You may have a similar situation. However it's nowhere as easy to access the passages on a BBC as it is on a 235.
And as FlyNavy says ignition timing can be a big factor. Do you have access to a distributor machine?
Have you tried disconnecting and plugging the vacuum advance hose to the distributor to see if that helps?
Pusher fans are really more of an air flow reducer and should not be used unless there is on option for a puller fan.

Thanks HO455...I try to be informative while presenting my situation as I find it limits how many times I need to say "yeah, I tried that"...but I still worry that I might "lose my audience" if I am too long-winded. Too many times on the witness stand, I guess?

Your first thought lines up with what I was wondering about...restricted water passages...but my 1989 454 is old and new at the same time as when we had the heads off and oil pan removed (at my friends shop), the motor looked as if it hadn't had any miles put on it since new. We did not specifically look for water passage restriction at that time, but nothing jumped out at us either. I also realize that even without putting miles on a motor, the water passages are susceptible to the corrosive elements from day one...and may actually be more susceptible due to non-use (water/air just sitting in the passages) as my Suburban sat non-op for 4 years before I purchased it. Like you said, not real easy to get to the passages on a BBC...so that may have to wait until the motor comes out when the body and paint work gets done?

I haven't received the "cooling info" from Greg (FLYNAVY) yet, but I am curious about my timing...and will try plugging the vacuum advance to see...although my mechanic buddy usually sets things up "by the book" and there is no indication of pre-ignition/detonation as far as I can tell? I'm not sure if he has a distributor machine or not...but I'll ask. You didn't mention the carburetor...but I'm pretty sure it is a tad on the rich side, which should be better for cooling than being on the lean side...but I guess knowing that for positive would be a good thing as well.

I'm not quite sure what you mean about the pusher/puller fan air flow reducer situation...but I wouldn't give up my mechanical puller fan...I would just add an electric pusher fan in front of the radiator. The fan blade edge is just peeking out the back side of the shroud...but I could only get about another inch exposed IF I bought one of Hayden "short shaft" fan clutches...which I might try?

There is also the thought that 190 is nothing to complain about, and I am thrilled that I attained that "level of coolness"...so maybe I'm being a little greedy by wanting to be cooler? In any case...I do appreciate your input...as well as everyone else's!

Woody

[HO455]

Originally Posted by Beach-Burban

I'm not quite sure what you mean about the pusher/puller fan air flow reducer situation...but I wouldn't give up my mechanical puller fan...I would just add an electric pusher fan in front of the radiator.

Woody

Currently other than the grille you have no restriction in front of the radiator. Adding a pusher fan will restrict air flow through the radiator in the area where the fan mounts and in the center of the fan where the motor is. In addition at speed it is possible for the pusher fan to create a high pressure bubble that prevents air from entering the fan blades and the radiator behind them. Even though the fan blades are moving they are still flat objects that 20-30% of the incoming air will hit and bounce off of. The faster the incoming air is the harder it bounces off of the blades.
The devil is in the details when adding a pusher fan. Matching the performance of the 2 fans so they complement each other is where the real work is.
Some late model high performance Corvettes have both a puller fan and a pusher fan that the base model Vettes don't get. GM discovered a need for more cooling and then carefully engineered a solution. I have no knowledge as to how or when the fans operate or are controlled. Or even what the goal was. I've just seen them and was surprised to see the pusher fan.

I just noticed you have A/C. How is the air flow through the condenser?

[FLYNAVY30]

woody, apologies, I never received your email....checked regular and the junk folder. Would you mind resending? GPaules03@gmail.com and Ill get it right out to you.

Thanks!

[Beach-Burban]

Originally Posted by FLYNAVY30

woody, apologies, I never received your email....checked regular and the junk folder. Would you mind resending? GPaules03@gmail.com and Ill get it right out to you.

Thanks!

Thanks Greg...new email sent! I very much appreciate the assist!

Woody

[Beach-Burban]

Originally Posted by HO455

Currently other than the grille you have no restriction in front of the radiator. Adding a pusher fan will restrict air flow through the radiator in the area where the fan mounts and in the center of the fan where the motor is. In addition at speed it is possible for the pusher fan to create a high pressure bubble that prevents air from entering the fan blades and the radiator behind them. Even though the fan blades are moving they are still flat objects that 20-30% of the incoming air will hit and bounce off of. The faster the incoming air is the harder it bounces off of the blades.
The devil is in the details when adding a pusher fan. Matching the performance of the 2 fans so they complement each other is where the real work is.
Some late model high performance Corvettes have both a puller fan and a pusher fan that the base model Vettes don't get. GM discovered a need for more cooling and then carefully engineered a solution. I have no knowledge as to how or when the fans operate or are controlled. Or even what the goal was. I've just seen them and was surprised to see the pusher fan.

I just noticed you have A/C. How is the air flow through the condenser?

HO455...The A/C condenser does take up the entire opening leading to the radiator and there is also an external trans-cooler in front of the condenser on one side, so I imagine combined they slow things down a bit...which is why I thought an electric pusher fan installed behind the condenser and up tight to the radiator would actually speed things up some. The condenser allows decent flow through the fins as I can see through them better than I can though my new radiator! Having the condenser in front of the electric fan should diminish the "bouncing off" effect, don't you think? I totally get what you mean with the "balancing act" between the two fans...actually seems like "trial and error" is the only way to figure it out (unless one has a wind-tunnel or other sophisticated facility of some sort). I read the link you sent...really good info there...and it seems like my set-up with regards to fan placement within the shroud and fan clutch proximity to the radiator fall into what they say it should be (1/2" of my fan blade edge extends beyond the shroud...and my fan clutch is 3 1/2" from the back side of the radiator). While those are the minimums they suggest, moving the fan blades further out of the shroud by using the short shaft Hayden fan clutch will also move the fan clutch further from the back of the radiator by one inch (just over of the 4" max they talk about...and some say 4" is too much anyway!). The other thing is that the Hayden short shaft clutch is only available as Heavy Duty, and the Severe Duty has a more aggressive lock-up feature, which is recommended. For $60, it might be worth buying it to know for sure? Ha...something else to think about! Thanks for the follow-up info...I feel as though I'm absorbing some education that actually appeals to me!

***UPDATE*** I was reviewing the notes I made before I started removing the original parts and realized that the measurement between the radiator and the face of the thermal clutch is actually 1 3/8" not 3 1/2" (not sure where I got that number from???) so using the short shaft clutch would only put the total distance away at 2 3/8" (more than the optimal distance, but should still register the heat enough to work correctly). That would move the back edge of the fan blades out of the shroud to a total of approximately 1 1/2", which could make a difference. If it doesn't help, I can always change it back as I'm kind of getting good at unbolting these same parts!

Woody

[FLYNAVY30]

email sent Woody!

[Beach-Burban]

Originally Posted by FLYNAVY30

email sent Woody!

Got it; read it; understood it...and appreciate it!

Woody