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Cooling Issue

I love my Chevy Chevette!
Posts: 1
Joined: 09/12
Posted: 09/26/12 09:36 AM

I have a 67 427/435 BB. The car has not been out in about 8 months. I brought it out and did some maintenance, than ran it about 20 miles, upon return I was blowing coolant out of the overflow tube. Temp gauge was at 210, shut it down and let it cool. I have never had a cooling problem with the car, complete overhaul of the cooling system was completed 4-5 years ago, the car only gets driven 200-300 miles a year with only 56k orignial miles on it. I drained the coolant, pulled the thermasta and checked it, it worked at the 160 as indicated. Replaced it with a new one added fresh coolant. Ran the engine and I dont seem to be getting any curculation? however the coolant leval is dropping and rising as it gets hot? Am I just imaginiung things here? Could the origianl coolant have evaperated and I may have just been low on it? Any help would be appreciated.  Confused  

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My first time was in a Chevy
Posts: 241
Joined: 04/12
Posted: 09/26/12 01:10 PM

have you replaced the radiator cap.. or tested the cap to verify it holds pressure...  i have run into a LOT of bad caps lately...   if the cap fails to hold pressure you will loose coolant..

you might want to change to a 180 or 192F thermostat... so there is a higher temp differential to allow the radiator to loose heat to the air flowing through it better..

most of the time.. it takes a 192F thermostat and a 16 pound cap to control high horsepower motors cooling systems..  yes.. the car will run at 195 to 215F... but it will stay right there..

do you have an infrared thermometer? so you can point at various parts of the engine... also when the engine comes up to operating temp... some mechanics will wave the infrared thermometer across the radiator.. looking for cold sections indicating clogged tubes...

hot tube means water is flowing..

cold/cooler than other tubes.. means no coolant flowing..   blocked radiator tubes reducing the amount of cooling ability of the radiator..

if you don't have an infrared temp gun...

a few more things....

engines that sit for long periods can have some sludge build up in the bottoms of the cooling system around the cylinders..

engines that sit for long periods can also have corrosion issues with the water pump impeller... where its just eaten away.. fails to circulate coolant at the proper speeds...

blocked passages and smaller hoses can also effect the system..

how the system works... the thermostat is closed...  preventing circulation into the radiator... the water pump pushed water into both sides of the block... around the cylinder walls.. up through the back of the heads.. forward through the heads to the coolant crossover passage in the intake...  since the thermostat is closed.. it is forces through the heater hose and the bypass hose.. both of them lead back to the water pump...  

this allows the water pump to circulate the coolant around and around until it picks up enough heat to open the thermostat....

a few things NOT discussed...  boiling points increase 3F for each pound of pressure increase..
this is one of the reasons you have a 13 or a 16 pound radiator cap...  takes the boiling point of 50/50 to 70/30 coolant / water to around 265F...

now... because the bypass and the heater hoses have smaller diameters than the water pump can flow at high speeds... there is mechanical pressure build up by the pump in the block and heads...  this is also why  the coolant will flow through the heater core.. going the long way..

but at cruising to high engine speeds...  this increased pressure in the blocks and heads increases the boiling point around the cylinders... exhaust ports.. exhaust guides.. exhaust valve seats.. spark plugs... preventing the coolant from boiling in the additional heat areas ..creating steam bubbles that go upwards and force coolant down away from the back of the thermostat...

steam does not transfer enough heat to the wax to open the thermostat... so the engine gets hotter and hotter...   drilling a hole allows some of the air bubbles to bypass..

but.. wait...

with the thermostat closed...  the coolant in the radiator is stopped... so the mechanical fan and the ram air through the radiator can take the heat out...

if you remove the thermostat... you will have coolant flowing through the radiator so fast that it can never be cooled properly.. taking forever to get the engine warm.. and once you get it hot... it MAY become a runaway cooling system.. where it just gets hotter and hotter...

think about those neat restrictions the nascar guys install.. guess what.. ever seen them change the tape on the grill..  thats how they control the cooling..  too much opening . the engine runs too cool...   too small opening.. the engine overheats...

radiator pressure testers are available at some parts chains.. in the loan a tool section...

this will allow you to test the cooling system.. and also the cap...

since you have a fairly exotic corvette...  you will probably want to have a correct radiator cap.. at least for displays... but you can run a conventional cap for driving...  you will want to check the cap... the disc in the center of the rubber on some models is loose... others its spring loaded upwards..... get the spring loaded version..

lastly... i am taking that you have a fixed blade fan.. not a fan clutch on that model... if you have a fan clutch.. post.. as they can go bad also...

you may want to install the thermostat housing without the thermostat and fill the cooling system.. start and run the engine to see how fast the coolant actually circulates through the radiator.. being pushed by the water pump impeller...

this is just a test...  

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V-6 Camaros rule!
Posts: 88
Joined: 01/12
Posted: 09/26/12 07:03 PM

Cooling issue welcome aboard:

I know what your saying when you only drive them a few hundered miles a year.

I would say your cooling system is filling up with mineral deposits. These are my suggestions.

Take the radiator out have it bolied and pressure tested at a radiator shop. Install a new 16lb. radiator cap, a NEW 180* thermostat, and flush the block out. You could add a flush and drive it, but if it's overheating don't.It can easily be done when you remove the radiator, and the thermostast. Just reinstall the goose neck with the hose, and no thermostat. Let the water into the goose neck.You can run the engine or not,if you do run it it will circulate the crap inside the block. Then do a 50/50 or a 73/30 more coolant then water. Let it idle, and if you can do this, the side the radiator fill is on maybe get a couple 2X8" under that side front tire. It will help bleed the air out of the system quicker. I know what guys that own Vettes have come up with for changing the oil..

Thats another thing that you should keep an eye on. The less you drive that BB the change the oil more frequent. The oil will become acidic. It could hurt engine bearings, and other internal parts...Agagin my 2 cents... Grin  Cool


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V-6 Camaros rule!
Posts: 88
Joined: 01/12
Posted: 09/30/12 12:27 AM

Use the proper coolant, for your older cooling system type. Install a 180* thermostat. Hopefully this helps you and your on the road to your cooling system woows.... Blush



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