Well I just got my 78 back from having the rear rebuilt, and now for some odd reason, it is very slowly overheating, the more i drive it, the more it heats, and this isnt with it sitting in traffic, this is cruising along at 65 mph. I am a little confused by this as the car can sit in my driveway and idle for an hour and never leave the 200 mark. My current set up is one 16' electric fan mounted in front of the rad, and one 12' electric fan mounted in front of the rad. The car hasnt boiled over, but the guage reads at right before the 280 mark with only 5 minutes of driving at normal speeds. I checked the flow of the thermostat and I had a lot of pressure in both the upper and lower rad. hoses. Also the water pump and rad. are new as well are the hoses and it has a 160 degree thermostat. Any help or suggestions for diagnosis?


Also another weird guage problem I am having is when i start my car, my GEN light stays on and my volt guage reads pretty low, until i tap the acc. pedal, then the light goes out and the guage reads around 14v. I had a 77 monte carlo that did this exact same thing. The alt. is new.
Thanks
---Chris


[Modified by Today's problem is.., 2:37 AM 4/2/2004]

 

Did the gear ratio stay the same during the rebuild or were bigger ones installed, like from a 3:08 to 4:11? Just curious. That would make the engine work harder at highway speeds and create more heat for one thing.

 

I left the rear gear ratio alone, I had intended on installing larger gears, but the car already had a 3.56 ratio in the rear, which is what i wanted anyways. I had it rebuilt due to the right yoke coming loose and the left wasnt far from it after i saw the parts that came out.

 

How long have you had the elec. fan set-up? Have you driven it in high heat with that set-up? Are you sure there are not air bubbles in the radiator- i.e. was it recently refilled?

 

Also can be a exhaust clogging!!!

 

Chris, I agree with the others on the overheating problems and the first thought to add would be a failing head gasket. Put a pressure tester on the radiator and see if the pressure builds higher than normal. As far as the GEN light problem I have seen this behavior on similar Delco charging systems and it was normal for those systems,but not on your Corvette.You said it was a new alternator,make sure the belt is tight and not slipping,that the pulley is the same size and the nut is tight,but I don't think it will cause any problems as long as you bump the idle up so it charges every time. Maybe it is an alternator that requires slightly higher RPM to engage the voltage reg.
:cheers:

 

I have only owned the car for 9 months, I bought it without and engine and it sat for about 6, in the last 2 months i have put the engine in it and rebuilt the front end, so ive never run it with anything but the electric fans. This is my first corvette, so Im not all too familiar with their problems. The exhaust on the car is new with no cats, headers 2.5 pipe with flows. As for the head gasket, the engine is newly built, and I did a comp. test after i built it and was pushing between 235-255 lbs on each cyl. I went out tonight and installed an air fuel guage and saw the engine was running lean while cruising. My initial idle timing was set at 16 degrees, so i bumped it down to 10, now i am running at a proper mixture while cruising, but it still ran around 280 and wouldnt go down while i was driving it.

 

make sure al air is out of the cooling system, and double check the gauge
280 IS HOT :eek: if it has got that hot i'd change the oil also :thumbs:

 

Strange problem. Make sure its not your guage, temp sensor or associatded wiring that is faulty. :cheers:

 

I would check the thermostat, it could only be opening partially allowing adequate cooling during idle but insufficient flow during cruise. Try a run without a thermostat installed and see if it cures your problem. Also, make sure you installed a lower radiator hose that has the spring in it, if it doesn't have the spring the hose could be sucking shut and restricting flow at cruise speeds. :chevy

 

I only got to this point, but from what you say, are you sure the sending unit is working correctly. Your not losing antifreeze and the fans are working but you keep getting a high reading despite not having done anything to the engine. Get a new GM temp. sending unit. Like Yogi said, if your at 280 and you pull over to the side of the road and let it idle does the temp come back down, If so the spring is missing from the lower rad hose.


[Modified by killain, 9:08 AM 4/2/2004]

 

Sometimes a 160 thermostat can run hotter than a 195 thermostat. Example, your engine heats up initially and the radiator is still cool, the thermostat opens at 160 and the temperatures are somewhat equallized, if the engine coolant temp drops below 160 then the thermostat closes and the water in the radiator should cool down as air flows through it. But, with a 160 thermostat, it doesn't take long for the thermostat to re-open and the water in the radiator hasn't had very much time to cool off. Eventually you are left with a thermostat permanantly open and water flowing so fast through the radiator that it never gets a chance to cool off. If you run a 195 thermostat, the water in the radiator has longer to cool before being flooded with hot water from the engine.
This sounds pretty complicated, but as an example I ran a "Fail Safe" thermostat once (never buy them they are junk) They have a locking mechanism that makes them fail in the open position, and when it was locked open it ran hotter than when I replaced it with a 180 thermostat.

Normally this wouldn't be a problem at all but with your fan setup you may want to see how well you are getting air through your radiator. If it can't sufficiently cool you may want to run a hotter thermostat.

Just my $.02

 

Lean cars run hotter. Adjust your mixture.
Check lower radiator hose for spring.
Electric fans need good current and 12+ volts. If your alternator isn't deivering the goods then the fans will not work as well (or relay may not turn them on)
If you are moving ie on highway then the fans do not do a lot. Most of the cooling is provided by movement not fans at highway speed.
Sounds like a head gasket. Check your oil and water for gunk. Chocolate thickshake is what you will see if you are getting water in the oil.

Check out http://www.corvettefaq.com for other cooling tips.

Good luck.

 

I will also add that the fans may simply not be up to the job. I have a stock 350 with Flex-i-lite dual fans. On hot days with A/C on, they can't keep up with the demand, especially at higher rpm highway speeds and the temp. climbs. On cool days, never a problem. I have a Spal dual set-up in the garage waiting to be installed that hopefully will fix this.

If you have had motor work done and upped horsepower, etc, it is possible that your fans may be inadequate.

 

I would think that the fans in front of the radiator would restrict the amount of air going through it. All of the electric fan set-ups I have seen were pullers, not pushers as in your case. As for running without a thermostat, I disagree. This will only postpone the overheating process, not eliminate it. The thermostat serves not only as a coolant on/off valve, but also as a flow resitrictor. The coolant needs to spend some time in the radiator so that the heat can disperse through the fins. Another item to check would be the seals between the fans and the radiator, and the radiator and support. Air will take the path of least resistance, and around the radiator is easier than through it. Five bucks worth of foam rubber window seal made a big difference in my car. Also see if your lower air dam is adjusted properly, or even there. I would also mount the fans on the back of the radiator and not the front.

 

:iagree:

Sounds like the airflow is going around and not through the radiator. I had the identical problem: temp was low at idle, and I could drive stop and go around town all day, but once I opened it up on the freeway, it would slowly creep towards the red. My fun ended one day I did a little Blue Angels impression when my radiator hose blew at 70 mph and I pumped out a nice white steam trial just like they do at the air shows.

My problem turned out to be my radiator. I put in a new rad (a cheap one, too) and my temp has been fine ever since.

Good luck! :flag

 

:iagree: Make sure its not your guage, temp sensor or associatded wiring that is faulty. Also I would take out the thermostat and with a 1/8" drill. Drill 4 holes just inside the gasket seal. That is a new GM recommendation. Keep the water flowing during and after it closes. Bad thermostat have fryed lots of engines. :seeya Steve PS Hope it's not a head.

 

I agree with "thebruce". I've read all responses, all good. Mine sat for an extended peroid with a rad. that was only a year old. 1 summers driving convinced me I had a cooling prob. Pulled the rad had it chk'd. Most cores were plugged by God knows what. Recored rad.

 

I used my car as a daily driver for years and then one day it started getting hot at highway speed. I hadn't done any mods so I checked the radiator and the cores were plugged. No water flow = hot motor, and 280 is HOT
:auto:

 

Well I went through all the advice everyone gave me, my rad. water pump and hoses are all new since i just put the engine in, i replaced all those too. It turned out it was a bad sending unit, I purchased a new one and installed it into the intake manifold just to check the guage, and sure enough, i got a lot lower temp reading, so i borrowed a laser temp gun, and it is correct, so I guess I never really was running hot, just the illusion of it. Thanks to everyone for the great advice, helped me learn a lot more about my car.

---Chris :auto: