Engine over-heating need advice

[clarkd]

I have a '74 with a recently rebuilt 350 (300 miles on it). Over the course of 15 miles the engine gets extremly hot (225+). I have checked the radiator, theromstat, hoses, flow tested the water pump, and checked the plugs to see if it is possble that it was running to lean. Does anyone else have any suggestions?

Thanks

 

[Bob Chadwick]

We need more info on the driving conditions when it gets hot and ambient air temperature.

Basic starting points. Assuming a clean system, heating at freeway speeds suggests missing seals or chin spoiler allowing air to bypass or change the flow of air from through to around the radiator. Heating in traffic could be a bad fan clutch.

Also, the gauges on these cars can be off by a wide margin. You might want to get it hot and take it to a shop where they can shoot the thermostat housing with a temp gun and see what the actual temperature is.

Timing can cause overheating as well.

Mine can run as high as 225 on a hot day in stop and go traffic with the a/c on. At freeway speeds it generally stays around 200.

 

[bill81vette]

you might want to run a gardenhose thru you fins to see if there is debris (bugs,dirt,ect)built up on the fins from just years of being driven..i have to do my p/u every couple of years in the spring when i start using the a/c b/c it runs a little hotter than it should.....just a suggestion.


bill

 

[clarkd]

over-heat

Bob,
thanks for responding. The lst time I drove it it was about 85 out and I was cruising the freeway at about 70mph and the temp got to about 225 in less than 6 miles. I immediately turned around for fear of warping something.

I am curious about your point on the chin spoiler. I have removed the front fender facia from the car due to cracks in the composite material and am presently waiting a new fiberglass replacement. Is what your calling the chin spoiler the same thing? Also, i did check the clutch fan and it is OK. Regarding the gauge, i am assuming it is OK becuase the car was extremely hot. My thighs were actually sweating.

Thanks Bob.

Dave

We need more info on the driving conditions when it gets hot and ambient air temperature.

Basic starting points. Assuming a clean system, heating at freeway speeds suggests missing seals or chin spoiler allowing air to bypass or change the flow of air from through to around the radiator. Heating in traffic could be a bad fan clutch.

Also, the gauges on these cars can be off by a wide margin. You might want to get it hot and take it to a shop where they can shoot the thermostat housing with a temp gun and see what the actual temperature is.

Timing can cause overheating as well.

Mine can run as high as 225 on a hot day in stop and go traffic with the a/c on. At freeway speeds it generally stays around 200.

 

[clarkd]

Bill,

thanks for the reply. I have done all of that as well as had it flow checked. I have removed the front fender facia becasue of cracks and plan on installing a new one as soon as it comes in. Do you think that with this part missing, it could effect air flow around the radiator?

Dave

you might want to run a gardenhose thru you fins to see if there is debris (bugs,dirt,ect)built up on the fins from just years of being driven..i have to do my p/u every couple of years in the spring when i start using the a/c b/c it runs a little hotter than it should.....just a suggestion.


bill

 

[Vettehead Mikey]

Do you think that with this part missing, it could effect air flow around the radiator?

I'll bet a dozen donuts that this is the cause. My '73 couldn't go over 45 mph without it.

 

[Dave Z]

Mine was running about 220. I replaced the thermostadt with a 165. Still didn't solve the problem. I noticed the radiator cap was in pretty bad shape, I'm sure it was the original. Replaced it with and 16lb cap and shaved off 10 degrees...now I'm running 200 constantly. Still not where I want it to be, but it helped.

 

[Dave Z]

...err...that is shaved 20 degrees...

 

[Bob Chadwick]

I am curious about your point on the chin spoiler. I have removed the front fender facia from the car due to cracks in the composite material and am presently waiting a new fiberglass replacement. Is what your calling the chin spoiler the same thing? Also, i did check the clutch fan and it is OK. Regarding the gauge, i am assuming it is OK becuase the car was extremely hot. My thighs were actually sweating.

In a word yes. I'm not sure of the setup on yours but I have a little lip under the front of the car that directs air. Without it, it will not get the air flow that it needs. The fact that it is happening at speed reinforces the thought.

I'd have to look it up to explain it with any detail but the aerodynamics of the car creates pressure points in the air going through the radiator with the low pressure and high pressure areas seeking equilibrium and creating air flow through the radiator. The chin spoiler is part of that process as are the seals around the radiator.

 

[clarkd]

Thanks Mike. I think that this is the logical step. Much appreciated!

Dave

I'll bet a dozen donuts that this is the cause. My '73 couldn't go over 45 mph without it.

 

[clarkd]

Seals are good. think that I will wait to the front comes in and give her a whirl.

thanks to you all for your advice1
D

In a word yes. I'm not sure of the setup on yours but I have a little lip under the front of the car that directs air. Without it, it will not get the air flow that it needs. The fact that it is happening at speed reinforces the thought.

I'd have to look it up to explain it with any detail but the aerodynamics of the car creates pressure points in the air going through the radiator with the low pressure and high pressure areas seeking equilibrium and creating air flow through the radiator. The chin spoiler is part of that process as are the seals around the radiator.

 

[photovette]

On '77 L-82's, there was a rubber extension on the air dam. These are no longer available, though they can be made from strips of hard rubber. GM thought it was necesssary to add more cooling air flow to the L-82, and since quite a few of us have increased horse power at and beyond L-82 specs--some of us are having high temperature problems. Beyond the normal causes of overheating that is.