Small block 385 running hotter than normal - Chevelle Tech
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post #1 of 11 (permalink) Old Jul 12th, 20, 11:20 PM Thread Starter
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Dan
 
Join Date: Aug 1999
Location: Lansing, MI
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Small block 385 running hotter than normal

Recently while driving my chevelle I forgot to turn on the electric water pump. It got up to about 250 degrees and pushed some coolant out of the radiator cap before I realized it and turned the pump on.

Typically on an 80 degree day driving around town the car will run about 180, might get up to 195-200 at a stop light before the fan comes on, then quickly comes back to 180 when I get going again. Cruising at a steady 60 mph its stays at a steady 180 degress.

After the overheat incident, I got it home and let it cool off I cleaned up the mess of spilled coolant and topped the system off. Next time I drove it around town it was getting up around 210 at stop lights and took way longer than normal to cool down at all and would only come down to around 195.

I replaced the thermostat (180 degree) and it didnt change anything

Replaced the 18lb radiator cap, no change.

Replaced the Autometer temp gauge thinking (hoping) maybe it had failed, no change.

Tonight drove out of town for about 15 miles at a steady 60mph and it slowly kept creeping up till it got to 220 degrees. Stopped for a couple minutes, left it running and it came down to 210. Drove back home and again it crept up and was about 225 by the time I got home.
I borrowed a pressure tester, pumped it up to 15-16 psi, it didnt lose any pressure for the 15 minutes I let it sit. Started the car up and let it idle till it got up to 180 degrees, the pressure slowly came up to about 25psi and then it barfed a little coolant out of the pressure tester cap. At first I thought that indicated a problem but after thinking about it, without having a radiator cap in place to bleed off excess pressure it had to go somewhere.

So after all this im a bit stumped. I dont think I have a cracked head or block or blown head gasket but something has clearly changed. Also the engine seems to be running just as good as it ever has. Also the oil looks good, doesnt seem to have coolant in it and I dont smell coolant from the exhaust.

Thoughts on what to check next?

70 Chevelle 385 small block, 11.0ish compression
200cc alluminum heads, 64cc chamber
Comp xr300hr cam, 300/306 duration, .562/.580 lift
Dart airgap intake, 750holley
4:10 rear gears
3515 lbs w/ driver
12.32 @110 all motor, 11.31 @121 175hp nitrous

Have you driven OVER a Ford lately?
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post #2 of 11 (permalink) Old Jul 12th, 20, 11:28 PM Thread Starter
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Dan
 
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Re: Small block 385 running hotter than normal

Forgot to mention, when I got home and shut the car off, it sat for maybe 5 minutes, the temp gauge was showing 230, using one of those laser temp guns checked it where the temp gauge sensor screws into the intake and it was showing 195. Its a mechanical gauge
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post #3 of 11 (permalink) Old Jul 13th, 20, 9:34 AM
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Re: Small block 385 running hotter than normal

What radiator and fan setup are you running right now? All original?
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post #4 of 11 (permalink) Old Jul 13th, 20, 9:45 AM
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pete
 
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Re: Small block 385 running hotter than normal

Quote:
Originally Posted by Dcairns560 View Post
Forgot to mention, when I got home and shut the car off, it sat for maybe 5 minutes, the temp gauge was showing 230, using one of those laser temp guns checked it where the temp gauge sensor screws into the intake and it was showing 195. Its a mechanical gauge

You may (emphasis on may) have gotten some air in the system. Try 'burping' it.

Start with engine cold, remove radiator cap, run engine until thermo opens (you can see the flow begin into the radiator). Let it run awhile (210 degrees, or so). Check fluid level, add as required. Put cap back on and take it for a spin. See what happens. I can't say that IS the problem, but it's free and may be helpful.

Pete
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post #5 of 11 (permalink) Old Jul 13th, 20, 10:09 AM Thread Starter
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Dan
 
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Re: Small block 385 running hotter than normal

It has a grifin universal aluminum radiator and the fan is a lincoln mark viii electric. Ive been using this setup for years with no issues.

I will try that suggestion to try and get any trapped air out of the system.

Thanks for the replies!
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post #6 of 11 (permalink) Old Jul 13th, 20, 11:30 PM Thread Starter
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Dan
 
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Re: Small block 385 running hotter than normal

Talked to the engine shop that I use today and explained the situation. He was pretty sure it was a head gasket and suggested I get ahold of one of those tools that detects combustion gases in the radiator. Picked one up from harbor freight and sure enough, the fluid changed color indicating combustion gases in the coolant. So im in the process of pulling the engine...
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post #7 of 11 (permalink) Old Jul 14th, 20, 1:01 AM
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Eric
 
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Re: Small block 385 running hotter than normal

You don't need to pull the engine for head gaskets.
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post #8 of 11 (permalink) Old Jul 16th, 20, 10:04 PM Thread Starter
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Dan
 
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Re: Small block 385 running hotter than normal

Quote:
Originally Posted by oldcutlass View Post
You don't need to pull the engine for head gaskets.
I know, ive done it in the car before. I have a bit of an oil pan leak too so I decided to fix it all at the same time. Not to mention its a whole lot easier to do everything on an engine stand.

70 Chevelle 385 small block, 11.0ish compression
200cc alluminum heads, 64cc chamber
Comp xr300hr cam, 300/306 duration, .562/.580 lift
Dart airgap intake, 750holley
4:10 rear gears
3515 lbs w/ driver
12.32 @110 all motor, 11.31 @121 175hp nitrous

Have you driven OVER a Ford lately?
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post #9 of 11 (permalink) Old Jul 16th, 20, 10:27 PM
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Marco
 
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Re: Small block 385 running hotter than normal

A few questions:

How many times did you run the car after you topped off the coolant?

If you ran it more than once did the temperature differ at all?

The thing that got my attention was when a bad head gasket was mentioned. There are more symptoms than just the engine running warm. Bubbling in the coolant reservior, indications of coolant leaking into the cylinder.

Short story:

Changing coolant on a motorcycle is much different than changing it on a car, the entire system empties out. Even with burping that motor can run warm after a couple of runs until the coolant system gets back to pressure and all of the air is removed. Because those water pumps are all mechanical I usually rip into the bike to get that pump spinning fast enough to circulate all of the new coolant, there is nothing fun about that process what so ever, the motors tend to run pretty hot. Once the system cools and the coolant begins to condense back it creates a vacuum sucking in the rest of the coolant.. (I think I have that right, brain is full). It might not be the coolant it might be the air that cools and condenses causing the vacuum.

Anyway, depending on how much fluid evacuated out of the system it may take a run or two and some burping to get things running accurately. I would think an electric pump runs continuously at the same speed regardless of engine speed (If I am wrong I would like to know).

Moral of the short story:

My rule of thumb, if a mechanic said it assume the much simpler explanation.
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post #10 of 11 (permalink) Old Jul 16th, 20, 10:58 PM
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Eric
 
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Re: Small block 385 running hotter than normal

An air pocket in a cooling system usually results in wild rapid swings in temp, not a slow increase. In post #6 he mentions that he tested combustion gases in the coolant, thats generally a head gasket.

You're just jealous because you can't hear the voices!

1967 Olds Cutlass 468 BBC/T400
1963 Plymouth Fury 440/Torqueflite
2007 Ford Mustang GT (momma's car)
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post #11 of 11 (permalink) Old Jul 17th, 20, 3:30 PM
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Marco
 
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Re: Small block 385 running hotter than normal

Quote:
Originally Posted by oldcutlass View Post
An air pocket in a cooling system usually results in wild rapid swings in temp, not a slow increase. In post #6 he mentions that he tested combustion gases in the coolant, thats generally a head gasket.
Thanks, I scanned right past that.

So much for my story..
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