Author Topic: Radiator Replacement & Cooling System Flush  (Read 7707 times)

Offline bd

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Radiator Replacement & Cooling System Flush
« on: August 21, 2013, 12:47:34 AM »
Apapted from the original topic, "radiator replacement"

1987 305 automatic with AC

Radiator needs to be replaced, is this a reasonably straight forward DIY job or are there any surprises I need to be aware of?
I will be replacing all the hoses while I am at it.

in particular....
>the shroud/fan being in the way issue
>the filling process to insure radiator is full and no air is in the system, etc.

Is any basic radiator from the parts store ok or are there certain brands to avoid?

Thank you

Radiator R&I is fairly straightforward.  Use a 1/2" line wrench on the transmission cooler lines.  You will likely lose some ATF from the cooler and lines when you disconnect them (less than a pint, but enough to make a mess).  Cap the cooler lines and have some rags ready to wipe up spilled fluid.  You should be able to loosen the lower two screws clamping the fan shroud to the radiator support then unbolt the shroud from the radiator upper mounting brackets (two additional screws) and tilt the shroud rearward enough to slide the radiator out; if there's not enough space, remove the two lower fan shroud screws completely and retry.  If your shroud is a two-piece affair, bolted together in the middle, you can unbolt and completely remove the upper half of the shroud to provide extra room.  Just be careful while sliding the core out and back in that you don't drag the fins and mash them over.  Inspect the rubber cushions that cradle the radiator and replace them if they are deteriorated from age or oil saturated and spongy.  If the cushions are oily, figure out why and correct the problem while you have the radiator out.  Evaluate the condition of all the cooling system hoses, radiator cap, coolant recovery bottle, freeze plugs, heater core, water pump, thermostat, and so on, and replace as needed while you have the system apart.  If there's oil in the coolant, determine its source.

Now is a good time to upgrade the radiator with a thicker core (additional rows); but be alert, because a thicker core may require different hold-down brackets and cushions, and could change shroud offset.  Depending on the reason you're replacing the radiator, you may want to replace the thermostat as well and flush the cooling system and overflow bottle, before installing the new radiator - this prevents gunk from flushing into your shiny new cooler.  If the coolant is less than clean or more than 6 months old and not extended life antifreeze, it’s best to flush the system and add fresh coolant, now.

Once the new radiator is installed, smear a small amount of brake assembly lube (or DOT 3/DOT 4 brake fluid) around the inside of the hose ends where they slip onto the hose barbs to make installation and adjustment of the hoses easier.  Do not use grease or oil!  Be sure to adequately tighten all of the hose clamps.

If you're not using premixed coolant, mix 50/50 to 60/40 with "distilled" water.  Distilled water is inexpensive and minimizes unwanted chemical action.  Fill the radiator completely with the proper mix of coolant and, with the help of an assistant, start the engine and bring it up to operating temperature at a constant high idle (1,200 - 1,500 RPM) with the radiator cap installed only to the 'safety' stop - not twisted tight, because you want to avoid building pressure in the system at this time.  Once the thermostat opens and water begins circulating (upper hose is hot to the touch and dash temp gauge reads normal or above), use a rag saturated with cold water to carefully remove the cap while maintaining fast idle.  Be very careful while doing this to avoid scalding!  Do not let the engine idle down with the cap off or scalding coolant will forcefully blow out of the radiator!  Fill the radiator to the top with coolant and install the cap tight.  Now, you can allow the engine to idle down.

Add only straight coolant to the overflow/recovery bottle to raise the level to the "Full" mark or just over.  As the engine cools, it will draw fluid from the overflow bottle and the level will drop.  Over the next few heating/cooling cycles, any air remaining in the cooling system will purge and vent through the bottle, so that all of the air in the “closed system” will be displaced by liquid coolant.  Monitor the coolant recovery bottle over the next few days and refill as necessary.

...A few questions...

What's the theory behind maintaining high idle through the process?  Is it to ensure circulation?

The engine comes up to temperature quicker and the water pump causes a greater draw-down of the coolant level in the radiator.  In other words, you get a better fill in the radiator.

And should the new fluid be added to the system while the fluid is circulating or does it not matter?

Fill the radiator completely before starting the engine.  Install the cap loosely.  As the engine heats, coolant will begin to flow and then stop in several repeating cycles as the thermostat opens and closes.  Again, be very careful during this process that you don't get scalded!  Carefully remove the cap (insulated with a soaking wet rag) as described previously.  Once the water begins circulating continuously, top it off and install the radiator cap and fill the coolant overflow bottle.

And, keep your fingers and toes out of the cooling fan!   :D

Must the levers for the heating/vent system be moved to any certain position?

Since you don't have a heater control valve on your truck, ignore the position of the dash heater controls.

I remember on my Honda Accord there was a bleeder by the thermostat, and when filling the radiator fluid coming from the bleeder indicated the system was full, I also think the heat lever had to be on.  I know these old 350 GM setups are different and it will be good to have an understanding of the basics.

There are no bleeder valves on the small block engines.  You have to bleed them the 'old fashioned way.'   8)

Btw- so I have all the parts prepared, what size caps will I need for the trans cooler lines?

Cut a couple of 4" long x 3/8" hoses and run a bolt into one end of each hose - instant line cap.  Slip one hose onto each steel line as you disconnect it.  If available, thread 1/2" x 20 inverted flare plugs into the transmission cooler fittings.   ;)

Concerning flushing...
Never did it before, is there any specific instruction on how this should be performed?

On the radiator upgrade...
Do you think it will be better to do it?  You had indicated possibly needing different mounting accessories.  Can I get these additional items from the parts supplier also?  Will this upgrade present any trick issues to deal with or is it also straight forward?

The AC has been removed from the truck however the evaporator(?) is still in front by the radiator.
Any opinions either pro or con to leaving it or removing it?

I cannot stress enough that throughout this process you'll be working with near-boiling water and a running engine.   Set the brake, and remain alert and mindful to avoid injury!   Don’t work alone....

Determining the method:
How you flush the cooling system depends on the condition of the existing coolant.  If the existing antifreeze is reasonably clean, flush using clean potable water from a garden hose.  If it's rusty, oily, or otherwise contaminated, use a chemical flush purchased from your local auto parts supplier.  A grossly contaminated cooling system may require repeated chemical flushing to scour it clean. 

Preparing to flush:
Open the radiator petcock and drain the old coolant into a large drain pan that will hold 3 - 4 gallons of liquid.  Coolant is toxic and regarded as hazardous waste.  Animals like the taste of it when left out in open containers and it can kill them, hence, transfer the expended coolant into sealable one-gallon containers as soon as possible for proper disposal. 

Close the petcock and refill the cooling system with potable water.  Start and run the engine to operating temperature using the criteria described in a previous post.  However, don't install the radiator cap tightly at any time during the flushing process, because you don't want to build pressure in the system.  Now, you're ready to add the chemical flush, or flush with plain water as previously determined.

Chemical flush:
Follow the instructions on the chemical flush container.  When your satisfied that the system is clean, drain and refill the cooling system with potable water.  Generally, follow a chemical flush with a fresh water flush as described next.

Fresh water flush:
With the engine up to temperature and running on fast idle, slip a fresh water garden hose into the radiator fill hole.  Open the radiator petcock and immediately turn the garden hose on, so that water refills the radiator and then just burbles out of the radiator neck - all while water is draining from the petcock and the engine is running.  The idea is to establish a balance such that the hose supplies fresh water to the radiator slightly faster than dirty water is draining out of the petcock, all while the engine is running at a high idle.  Constantly monitor the garden hose to maintain the proper balance between inflow and outflow.  Continue flushing until the effluent from the radiator runs clean.  Then drop the engine to a normal idle speed and shut it off.  Turn off the hose and let the radiator drain completely.

Once flushing is complete, decide whether to use distilled water or potable tap water:
The best choice of fluid to mix with common antifreeze is distilled water.  Distilled water has a neutral pH and is devoid of corrosive salts, abrasives and living organisms (collectively, contaminants) that can react with the fluids and metals comprising the cooling system.  Fewer contaminants benefit cooling system efficiency and prolong component life.  This becomes most significant when the cooling system contains aluminum components, since aluminum is more chemically reactive than either iron or brass.  This is why premixed antifreeze is manufactured using distilled water.  Nonetheless, in the absence of distilled water, potable tap water can be substituted with some degree of success.  But, cooling system performance maybe compromised with an unavoidable increase in monitoring, maintenance and long-term cost.  Candidly, distilled water is so inexpensive and available, it is difficult to imagine why it wouldn't be used.
  • Using premixed antifreeze or distilled water:
    If using 50/50 premixed antifreeze or a distilled water with straight antifreeze custom mixture, remove the two 1/4" NPT plugs from the sides of the cylinder block and drain the remaining water from the block.  At this time you may choose to install drain petcocks to make future servicing easier.  Reinstall the plugs (or petcocks) and close the radiator petcock.  If using premixed antifreeze, add to fill, including the overflow bottle.  If using distilled water and straight antifreeze, add alternately, one gallon of antifreeze then one gallon of distilled water; adjust the proportion of distilled water for other than a 50/50 mixture.  Fill the cooling system and overflow bottle as previously explained, adding only straight antifreeze to the overflow bottle.

  • Using potable tap water:
    Close the radiator petcock and fill the radiator with straight coolant (approximately two gallons).  Don't use premixed coolant after you flush, because the engine will already contain 1.5 - 2 gallons of 'clean' water.  Fill the cooling system and overflow bottle as previously explained.
Regarding a radiator upgrade:
If the engine has never run hot and the temperature is always stable to within about 5° of the thermostat temperature, don't worry about upgrading your radiator.  On the other hand, if the engine runs habitually hot, or if you plan on towing, or installing power adders (e.g., cam, heads, higher compression, etc), then a larger radiator may be in order.  You should be able to find a higher capacity radiator w/o having to alter the mounting as long as you don't go wild (like upgrading from a 2-row to a 5-row).  Many enthusiasts upgrade to a 4-row diesel radiator.  Your local parts house or radiator shop should be able to help with available, direct-fit options.

Regarding the condenser:
If you have no intention of reinstalling the A/C, remove the condenser.  It serves no purpose and is directly in the airflow that cools the radiator.  Think of the condenser as a net or coarse filter that catches dust, bugs and other airborne debris.  Debris that accumulates in the condenser fins decreases airflow across the radiator.

Whether you leave the condenser in the truck or remove it, you should cap the ends to keep it clean.  The same applies to the evaporator (located at the passenger firewall), if still in the cab.

Fitting all of this discussion together should give you a fairly good idea of "how to."  Even so, you may encounter a surprise or two.  But, that's just life as a mechanic.   8)
« Last Edit: October 11, 2016, 07:30:51 PM by bd »
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87 R10 Silverado Fleetside 355 MPFI 700R4 3.42 Locker (aka Rusty, aka Mater)