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Discussion Starter #1
I've had my 68 camaro since last august. It has the four gauge cluster on the console. SBC 400 (late 70s) and a TH350 automatic trans.

The temp gauge had always registered one small notch past the first large notch despite weather or distance driven. I guessed that was an inaccurate reading as it would likely be only about 120*. In Oct, after getting it back from the shop, the gauge started registering different temps. It will show temps raising pretty steadily on idle, but will go up to the yellow line (about 211*?) and then fall back a few notches and go back up to the yellow line while driving.



I was concerned that the t-stat wasn't opening, so I pulled out the pretty old 160* and put in a new (tested) 180*. intake was dry so I think the 160 t-stat had failed. Afterwards, I let the engine idle for about 5 minutes and temps sat at the beginning of the yellow line.
when I took it out for a drive, the temp would go back to the yellow line with acceleration and drop down to about 190* or so when I was idle at a light or off the accelerator. Air temp. was about 70*.



When I checked radiator coolant, it was low, so I added 50/50 coolant about a week ago. Yesterday, the coolant looked about 4 inches lower than my previous fill line (checked on cold engine). I think I'd only driven about 2-3 very short trips in that time. Radiator is unknown age, but a stock type with stamped reservoirs. I have not seen any puking out the overflow. The rad. cap is an unknown lbs rating. Am I checking this wrong? The level of coolant shouldn't change that much should it?



I have checked the temps in the engine bay with a laser a few times. block in front and on side by temp sender were at about 210*, top radiator hose was about 193*. Lower hose was around 160* something. It appears that the temp. gauge is reading pretty close.



Am I getting normal operating temps? Seeing the temp needle go in to the yellow part of the gauge is concerning.



Thanks, Tom
 

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Tom - These gauges - if factory installed or factory style have a resistor to "correct" the gauge. Also the sender is in the head on the drivers side. Both should be tested. Both may need replacement.

You can bench test the gauge and sender by following the referenced sticky. To do so you will need an Ohm's scale on a multi-meter. Also helpful if you have a potentiometer so you can send a known ohm to the gauge and see what it registers at which point you can either live with that scale or change senders, and or add resistance to get the needle where you would like it.

Here is the sticky on water gauge sender testing https://www.camaros.net/forums/19-electrical-wiring/198776-1969-camaro-water-temp-gauge-console-gauge.html

Brian
 
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Might want to get a pressure tester from the loan a tool deal at auto part store and check radiator for a pin hole leak. Those kind of leaks can typically not show up on the floor as the hole is so small the coolant evaporates when it hits the hot engine

with that said having 3-4" low of coolant in radiator should not cause a overheating issue
 

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I might point out that 400 is a bigger number than 396. If you have a SBC 400 with a four barrel good heads and a cam you are making nearly fifty percent more power than a BBC 396. As such you will need a BBC HD radiator and BBC fan (I prefer the newer 7 blade over the period correct five blade), and proper fitting fan shroud which is a problem with a SBC Camaro.

Big Dave
 

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As such you will need a BBC HD radiator and BBC fan (I prefer the newer 7 blade over the period correct five blade), and proper fitting fan shroud which is a problem with a SBC Camaro.

Big Dave
This fan shroud is for a BB (23") radiator used for a SB (motor mounted center of frame). What I have for my 327 using a 23" radiator

https://www.summitracing.com/parts/oer-3893814
 

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Discussion Starter #7
Thanks for all the input. I hadn't considered the fan size. I'll measure what is in the car. Now I'm wondering if I should shouldn't just have the radiator flushed and fully checked?
 

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Now I'm wondering if I should shouldn't just have the radiator flushed and fully checked?
a quick pressure test using a loaner gauge will tell you instantly if the radiator is leaking....but it won't tell you if the cores are plugged up

You are losing coolant so it is leaking from "somewhere"....and a not free flowing radiator will run hotter.

Obviously a good radiator shop could tell you on both issues
 

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Discussion Starter #9
Ok, trying to figure this cooling issue out, I checked a few things and finally pulled the oil filler cap from the valve cover, passenger side.


Is this what I think it is, frothy oil from a blown gasket??

https://ibb.co/Sv5T4Yq
 

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Possibly but doubtful. More than likely this is just condensation caused by not getting the car up to operating temps for a long enough period of time. Take it on a long drive and it will clear right up.
 

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^^^^, if the oil is chocolate milk....then you have a blown head gasket

as mentioned condensation inside the oil cap will cause what you see on it. Typically due to short drives where the motor does not operate at full temps
 

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Discussion Starter #12
Thanks guys. The oil was changed about 200 miles ago. It's slightly darker than I thought it should be, but Amber colored and thin looking, not cloudy.

I guess I'm back to the radiator being a potential issue. Can't explain why the cooling system is eating coolant.
 

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pull the sparkplugs....that will also tell you if its leaking by the color of the plugs ;)
 

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Discussion Starter #14
Well, Im at a loss. I put enough coolant in the rad. to raise the level about 3 inches, just below the fill tube. It drove well and temp gauge stayed constant. I checked the coolant level a day later and its back down to about 4 inches below the tube.

Yesterday I went for a short drive: idle is very low. stays down to between 650 and 550 and feels like it will die when at idle/stops. temp gauge runs back up to the yellow section again, doing what it was doing before - under load temp raises steadily, at idle/braking or coasting it drops back down to about 190 or so. This was a very short trip in the neighborhood with speeds up to 35 mph or so.

Think I'm off to the shop to have them figure out why the engine/rad is eating coolant.

T
 

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IIRC the coolant level in the radiator should be about 3" from the top.

You may just be puking out that amount through the overflow hose

With that said your temps, according to your gauges and assuming they are correct, are high so having the radiator flow checked or boiled out at a good radiator shop is in order


If temps drop quickly once you start driving to me that would suggest the coolant flow is being restricted. causing it to run hot idling. T stat or radiator. Assuming your WP is working right and your fan shroud is on
 

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Discussion Starter #16
new cooling issue - solved

I couldn't diagnose the problem but kept having the same issues: overheating, loss of coolant, oil leak and rough running. Took to the shop and they found a blown head gasket. Just got it back today - running so much smoother and cooling nicely. Wallet is certainly thinner, but I'm happy to have this sorted out.
 
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