radiator replacement

[p7387]

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

[bd]

Radiator R&I is fairly straightforward.  Use a 1/2" line wrench on the transmission cooler lines.  You will likely lose some ATF (less than a pint, but enough to make a mess) from the cooler and lines when you disconnect them.  Cap the cooler lines and have some rags ready to wipe up spilled fluid.  You should be able to loosen the lower two screws then unbolt the fan shroud from the radiator upper hold-downs (two additional screws) and lay the shroud rearward enough to slide the radiator out.  If it's too tight, remove the two lower shroud screws completely.  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 sliding the core out and back in, so as not to drag the fins and mash them over.  Inspect the rubber radiator cushions and replace them if they are deteriorated from age or spongy and oil saturated.  If the cushions are oily, figure out why and correct the problem while you have the radiator out. 

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 affect 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.  If the coolant is ethylene glycol base, less than clean, or more than 6 months old (in other words, not an extended life antifreeze), flush the system and add fresh coolant.  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.

Once the radiator is installed, wipe a small amount of brake assembly lube (or brake fluid) around the inside of the hose ends where they slip onto the fittings and radiator to make installation and adjustment of the hoses easier.  Do not use grease or oil!

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 temperature at a constant high idle (1,200 - 1,500 RPM) with the radiator cap installed only to the 'safety' step - 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 hot to the touch and temp gauge reading normal or above), use a water soaked rag 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 blow out of the radiator!  Fill the radiator to the top with coolant, install the cap tight, then you can allow the engine to idle down.

Add only straight coolant to the overflow 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 will be displaced by liquid coolant.  Watch the coolant bottle over the next few days and refill as necessary.

[PromiseKeeper]

if you have an advance auto parts in your area, i have some discount codes to save you a few bucks

[p7387]

Thanks for the detailed instructions BD, it will be very helpfull.

A few questions?

Whats the theory behind maintaining high idle through the process? Is it to insure circulation?
And should the new fluid be added to the system while the fluid is circulating or does it not matter?

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

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.

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

Thanks

[bd]

Thanks for the detailed instructions BD, it will be very helpfull.

A few questions?

Whats the theory behind maintaining high idle through the process? Is it to insure circulation?
And should the new fluid be added to the system while the fluid is circulating or does it not matter?

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. 

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!

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.'   

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 cap.  Slip one hose onto each steel line as you disconnect it.   

Thanks

[p7387]

Thanks again for the good tips and info

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 it 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?

Thank you again for your help

[bd]

Thanks again for the good tips and info

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 it 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?

Thank you again for your help

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!

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 or otherwise contaminated, use a chemical flush purchased from your local auto parts supplier - really foul coolant may require chemically flushing multiple times. 

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 may kill them.  Hence, transfer the expended coolant into sealable one-gallon containers 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 plain water flush as described next.

Plain 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 bubbles out of the radiator fill - 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 water to the radiator slightly faster than it's draining out of the petcock while the engine is running.  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. 

After flushing:
Close the petcock and fill with straight coolant (approximately two gallons).  Don't use premixed coolant if you flush, because the engine will already contain 1.5 - 2 gallons of 'clean' water.  Fill the cooling system and overflow bottle per previous posts.

Concerning 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 change the mounting as long as you don't go wild (like a 2-row to a 5-row).  Your local parts house should be able to help with available direct-fit options.

Concerning 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 (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.   

[nlauffer]

bd - You have written a great and detailed post about this.  I have replaced a radiator before and flushed my vehicles before, but I found information I didn't think about before.

I think this would make a great Tech Page

[Irish_Alley]

he is a walking(well maybe) but typing tech page

[p7387]

Yes, thanks again for the detailed explanation. You have given me a great knowledge base to start from. As i encounter "hidden supprises" i will check back in on the topic. Hopefully others will find the information usefull as well. I also like the idea of putting all this good info in one "tech page" type article for all to benefit from.