Hi Folks,
Ok, bear with me, I'm still a novice wrench turner...
My '69 427 runs way too hot. Here are the symptoms:
When moving slowly in regular around town traffic the temp gauge will get up to 250.
Moving at a little faster pace or on the highway, the temp is around 220-230.
On the highway, if I lay into the throttle good the temp will go right up to the 240-250 range.(I have been babying the car, not getting on the throttle, and basically not cruising yet, untill I get this problem fixed. I don't want to suffer permanent damage due to over-heating.)
My manuals have not come in yet so I have not checked the water/antifreeze mix/levels.(I have read that straight antifreeze will cause the temp to go up, but this much?) The level appears to be OK - It's close to the top of the radiator opening, and the expansion tank is about 1/2 full.
The inlet hose going into the thermostat has more pressure/firmer when hot than when cold.
The hose going to the heater core is closed off at this point with a ball joint to keep the interior cooler.
So, any thoughts on where I start looking? I guess I'm just not really sure of the telltale signs of a bad thermostat or bad waterpump or bad whatever so any tips from you guys would be much appreciated!
Thanks...
-Tom



[Modified by 427_Roadster, 4:24 PM 9/22/2001]

 

I would check the fan clutch first, then the thermostat.

 

Sorry, forgot to mention - A fan clutch eliminator is in use, and also the top part of the shroud has been trimed to accomodate a larger diameter fan blade.
-Tom

 

Are you sure you're really running those temps? I'd confirm the real temp first - Vette temp guages are notorious for reading too high. Find someone that has an IR gun who can read the "real" temp and see how that compares with the guage temp.

IF that test confirms your guage, I'd start looking around that shroud. Those need to be properly shaped and sealed for proper air flow - cutting it and putting in a bigger fan is counterproductive. Also, make sure the black plastic spoiler is in place at the bottom front. That's where your car breathes, and that spoiler is necessary to "scoop" air in.

 

I never got that hot with my big block, but I have only run it with a very large BeCool aluminum radiator. Are you sure that you have the correct water pump. If it is designed to run in the opposite direction, you could be in for some trouble.

I was able to get the temp much lower with Spal fans. Take a look at the this post I did on them a while back. http://forums.corvetteforum.com/zerothread?id=142434

Chuck

 

Sounds like thermostat to me - I would replace it - they only cost 5 or 6 bucks. When you put new one in make sure you get all the air out of system. Also make sure that you don't exceed 50/50 on your antifreeze to water mixture as that will cause heat.

 

Another good idea would be to check the radiator core itself!
If you find a guy with a IR gun, please let him check the core lines from bottom to top.
Sir Tripower from the forum had the same problem, running warm (210° when on the Autobahn, OK not this much compared to you)
But he found out by this method that his bottom core lines were clogged (significant Temp. difference from on to the others, from bottom to top, talking of more than 100°F!)
Might not be the cheapest fault, but its worth a try!

 

lyonsh makes a good point about the front spoiler- also make sure that the foam seals around the perimeter of the radiator are in good shape.
Something else that was a problem for me shortly after I bought my Vette was the fact that the Q-jet, which appeared correct, was actually the smallblock version & was therefore jetted way too lean for my bigblock. Lean jetting definitely adds to cooling problems. Good luck.

 

@ Les: Absolutely correct! I forgot the lean condition!

Although I have to say that my front spoiler is missing, but even at 95°F outside the car does stay at 185°.
I run an oilcooler and an hidden electric fan.
Without the E-Fan the temp rises to about 210-215 but can still be managed.
I have a new rad core in, so I guess this is one main reason!

 

Here's what I did to fix my 1969 427's overheating problem:

1) disconnect all hoses and force water through each to be certain you have no flow restrictions.

2) connect the two hoses up to the heater inlets like it was when it came from the factory. Eliminate the shut off valve. It gets hot in the interior,so what, you can live with it-hey, you've got a Big Block Rat Motor!

3) Replace thermostat with a 160 deg unit (Napa heavy duty unit works well).

4) Check timing: too far retarded timing creates a hot running motor.

5) Replace fan clutch with correct factory style available from Zip.

6) Make sure your radiator is in good shape. Shroud should cover at least 1/2 of the fan blades depth.

7) Replace radiator cap on expansion tank with a new one. 16lbs.(Do the same with the radiator if it has a cap on it).

8) As mentioned previously, get a front spoiler and foam insulation to fill holes in the radiator support frame, etc.

9) Aluminum high flow Edelbrock (short leg) water pump.

10) Fill with tap water (not distilled), 1/2 gallon of anti-freeze (more if you see cold weather), and 1 bottle of Red Line's "Water Wetter".

I think that about does it. I am not sure which of these steps was the most rewarding, but I would think it was the t-stat.

My engine runs cool, not hot (and this is in Florida). Almost too cool, I may go up to a 180 deg t-stat.

Regards, mark :chevy :flag

 

Most of the people that have no big block heat problems are running either the spal fans or a replacement aluminum radiator (or sometimes both). I plan to take the second route, and purchases a Griffin aluminum stock replacement radiator. Everyone who has one LOVES it!

-Joe

 

Tom, it sounds as if you have mulitple problems here. First, as others have stated verify that you are indeed running those temps. I can't imagine driving a car when the actual operating temperature is 250 degrees. Can you spell engine failure? ;) Some folks will tell you to use a digital thermometer or go to a good radiator shop and use an infrared detecting device. While these are good suggestions, I use my wife's candy thermometer stuck in the neck of the radiator or overflow tank, depending on your application. Once you verify that you actually have those temperatures, then I pull the thermostat out and put it in a pot of water. Once it starts heating up, I note the temperature at which it is fully open, again using the candy thermometer. When the engine is hot and not running, spin the fan, if you have a fan clutch. Obviously with no fan clutch, you should have full time fan operation and therefore no in town problems. In addition, at highway speeds you shouldn't need a fan or clutch of any sort. Driving at 60 mph pushes more air through your radiator than just about anything short of a NASA wind tunnel.

If you are overheating on the highway that is an indication of inadequate cooling which can be caused by insufficient flow through the radiator. Obviously BB's run hot but when they were new, they were driven like a daily car. If you have your original radiator, you can have it flow checked by a competetant radiator shop. My 66 had overheating problems and I checked all of the things that others here have mentioned: timing, carb running lean, etc. When it was all said and done, my original radiator had deposits in the bottom and prevented full cooling of the water. The problem went away with a reproduction aluminum radiator. What type of radiator do you have? The other thing I check it to ensure that the bottom radiator hose has a spring in it. This prevents it from collapsing when the pump starts to suck water through it.

Replace the chin spoiler and make sure that your radiator face is free of any debris - bugs, leaves, road dirt etc.

As a final parting note, my neighbor has a 73 454, slightly modified for more hp, with air conditiong. He can run all day long with the air on, at highway speeds or around town, and not overheat. He has his original fan and clutch but he had his radiator rodded out and cleaned a couple of years ago.

Treat the cause, not the symptoms. Electric fans, 160 degree thermostat, water wetter, etc all are bandaids for an ailing cooling system. I don't fault folks for using them, but it doesn't cure the cause of the problem.

Just my $.02.

Gary

 

Don't laugh at this, but how would I be able to tell if I was running too lean? Are there any obvious signs, or should I have a good carb guy take a look?
The car seems to pull good down low and at highway speed without any hesitation-I will now be checking to make sure it is the proper carb also.
Thanks for all the replies :cheers: ...At least now I'm pointed in the right direction!
-Tom

 

I checked the numbers on my carb(thanks Les)and found that the unit is from a '72 350 200hp - #7042202. I guess this could definately be contributing to my problems.
Am I also getting way less performance than I should be? I would think this carb flows less fuel/air than the BB version?
How bad of a job is replacing a carb?
Thanks again...
Tom

 

Gary,
by now most all '69 motors have been rebuilt once or twice. Would you not agree that each time you remove cylinder wall material that the car will run hotter than before? This may be an explanation as to why so many Forim members have overheating problems.
I will also say that I remember hearing people with big blocks (BB 'Vettes in particular) say that they had problems with controlling their coolant temp. This was years ago when the cars were relatively new. Chevy originally installed a 190 deg thermostat in the 1969 BB 'Vette and was accepting the fact that these motors would run at 220 deg. That is not acceptable by today's standards and if you have a car that runs cool w/o some "band-aids" then good for you. I will agree a 180 thermostat would probably be a better choice than a 160, but hey, these cars are 32 years old and the fact is you might have to compromise some to make them run cool.

Tom, re: my first point (#1): I mean to disconnect one end of the hose and run water through it to see if it flows well. Also, remove the thermostat and force water through the opening in the intake and see if it flows out the water pump and the heater hose connection. Start with the cheap items before buying a bunch of new parts. You could possibly have a defective thermostat which is a $5 item.

Regards, mark :flag :chevy

 

There is no doubt that the BB's ran hotter than new. I was only saying that 250 is extreme from my point of view. I have heard annecdotal evidence that rebuilding may cause an engine to run hotter but since I have only rebuilt an engine one time I can't speak from experience. perhaps other can jump in on this comment.

I guess I was trying to say start at the basics and ensure that you have a 250 engine first. The temperature sending units and gauges are notoriously unreliable as others have posted. Once you know that it is hot, check the various components that can cause that: thermostat, timing, lower radiator hose, and radiator. My local radiator shop, owned by a mid-year owner, did a flow test on my original Harrison radiator and confirmed partial blockage. By back flushing he was able to get some of the silicate sediments to come out.

Gary