'73 Radiator Flush Procedure

[Peter G.]

I need to flush my radiator. I have had the car over ten years now and have not ever done this routine maintence. I notice the coolant in the radiator overflow tank is quite dark?

My car being a LS4 big block....and not seeing any drain cock under the radiator leads me to believe the only way to drain and refill the system is by pulling off the lower radiator hose. For those of you who are familiar with the big block..you can barely see the two lower hoses let alone work with the hoses and clamps!

Any suggestions are greatly welcomed.

Thanks in advance.

[Joe L.]

Re: '73 Radiator Flush Procedure

I need to flush my radiator. I have had the car over ten years now and have not ever done this routine maintence. I notice the coolant in the radiator overflow tank is quite dark?

My car being a LS4 big block....and not seeing any drain cock under the radiator leads me to believe the only way to drain and refill the system is by pulling off the lower radiator hose. For those of you who are familiar with the big block..you can barely see the two lower hose let alone work with the hose and clamp!

Any suggestions are greatly welcomed.

Thanks in advance.

Peter------


There should be either a drain cock or a pipe plug. Either might be difficult to access, but one or the other should be there.

Also, see the procedure I recommended in another similar post in the last hour, or so.

[Peter G.]

Re: '73 Radiator Flush Procedure

Thanks Joe...I have an original Harrison radiator so if it is supposed to have a drain cock or plug it should be there? I will take another look see. Any thoughts to if it would be on the bottom or engine side of the radiator?

I did quite a bit of refreshing of my older restoration last month and it has been so cold and snowy here that the car is covered up like a shrink wrap covered with three ....yes three car covers on her. (I know what your thinking....he's is a few tools short in his tool box, but they weren't doing any good in the bottom of the closet so I put them on the car together).

[Duke W.]

Re: '73 Radiator Flush Procedure

In order to thoroughly drain the system you need to remove the block drain plugs. They are just above the pan rail, about halfway between the front and rear faces of the block. If they are hex use a six-point socket and a breaker bar and "shock" them use. If the hex is okay reuse them with pipe joint compound on the threads or replace if they are bunged-up. Only tighten them enough with a small ratchet so that they don't leak. This is likely no more than 10 lb-ft. (There are no torque specs for NPT threads. They should be tighted only enough that they don't leak.) That way they will break loose easily the next time.

Do a couple of water flushes - fill with a garden hose, let it warmup to operating temperature, then shut off the engine, let it cool for an hour and do the same. Then fill with a 50/50 solution of Zerex G-05 and distilled water. The capacity is about 18 quarts, but check you CSM.

When you fill the radiator with the engine bounce up and down on the bumper to see if you can add more. When it won't take anymore, start the engine and monitor the level with the cap off. When the thermostat opens the radiator level should drop, so add more until it's near full. It's a good idea to drive the car around the block a couple of times (cap off) to get all the air to purge/

Some recommend to remove the thermostat housing to fill the blocks, but I've never had to do that on any car following the above procedure.

Duke

[Terry M.]

Re: '73 Radiator Flush Procedure

I need to flush my radiator. I have had the car over ten years now and have not ever done this routine maintence. I notice the coolant in the radiator overflow tank is quite dark?

My car being a LS4 big block....and not seeing any drain cock under the radiator leads me to believe the only way to drain and refill the system is by pulling off the lower radiator hose. For those of you who are familiar with the big block..you can barely see the two lower hoses let alone work with the hoses and clamps!

Any suggestions are greatly welcomed.

Thanks in advance.

Pete
If you have the OEM copper radiator there should be a drain plug on the bottom of the passenger side header tank. It should have a right-angle fitting with a hex plug in it. It will be difficult to impossible to get the hex plug out without damaging the right angle fitting connection to the header tank. There is little to no room to get a back-up wrench on the right angle fitting to absorb the torque needed to loosen the hex plug. The path of least resistance/damage is to disconnect the lower radiator hose, if you can get to that. There will also be little room to move the lower radiator hose off of the radiator fitting. I sometimes think they build the car around the radiator and hoses. Best of luck.

[Joe L.]

Re: '73 Radiator Flush Procedure

Thanks Joe...I have an original Harrison radiator so if it is supposed to have a drain cock or plug it should be there? I will take another look see. Any thoughts to if it would be on the bottom or engine side of the radiator?

I did quite a bit of refreshing of my older restoration last month and it has been so cold and snowy here that the car is covered up like a shrink wrap covered with three ....yes three car covers on her. (I know what your thinking....he's is a few tools short in his tool box, but they weren't doing any good in the bottom of the closet so I put them on the car together).

Peter------


It's on the RIGHT side tank. My recollection is that it's on the engine side but it's possible it's on the bottom.

[Duke W.]

Re: '73 Radiator Flush Procedure

Pete
If you have the OEM copper radiator there should be a drain plug on the bottom of the passenger side header tank. It should have a right-angle fitting with a hex plug in it. It will be difficult to impossible to get the hex plug out without damaging the right angle fitting connection to the header tank. There is little to no room to get a back-up wrench on the right angle fitting to absorb the torque needed to loosen the hex plug. The path of least resistance/damage is to disconnect the lower radiator hose, if you can get to that. There will also be little room to move the lower radiator hose off of the radiator fitting. I sometimes think they build the car around the radiator and hoses. Best of luck.

Wouldn't it be easier and less risky to just get a few feet of vinyl tubing and siphon the old coolant out of the radiator (since the cap it on the side tank) rather than messing with the drain plug or radiator hose?

Duke

[Peter G.]

Re: '73 Radiator Flush Procedure

I have a suction tank I used for oil changes on my Mercedes that recommended vacuum from above rather than gravity drain. I did both of course. I thought of using that apparantus to suction the radiator, but normally you can't get a hose down very far into the radiator due to internal tanks?

A lot of good information from all...thanks it will probably be May before I attempt this and I'll let everyone know my out come.

[Terry M.]

Re: '73 Radiator Flush Procedure

Wouldn't it be easier and less risky to just get a few feet of vinyl tubing and siphon the old coolant out of the radiator (since the cap it on the side tank) rather than messing with the drain plug or radiator hose?

Duke

That would certainly be lass risky and far more convenient for a manual transmission, but as Peter mentions not so much for an auto transmissi0on car.

[Mark E.]

Re: '73 Radiator Flush Procedure

Duke's method will work. But the engine drain plugs on most cars I've owned either would not budge with significant torque or were not accessible.

I found this reverse flushing method effective over the years:

- With the engine cool, disconnect the upper radiator hose from the thermostat housing. Plug the thermostat opening with a large plug (if you have one) or pack it tight with plastic then a rag. Loosen the upper radiator hose from the radiator, and rotate it so the loose end of the hose discharges water in a workable direction.

- Disconnect both heater hoses at the engine. Plug the block's lower heater hose nipple.

- Connect a garden hose to the upper heater hose nipple. Use water pressure from the hose to reverse flush the block and radiator. The reverse water flow will be: intake manifold, heads, block, water pump, lower radiator hose, up the radiator, then out the upper radiator hose.

- Flush until the discharge water is clear. Then a little longer.

- Drain and flush the expansion tank separately. The heater core is delicate, so if flushed at all, do it gently and separately.

- Renew hoses and clamps; refill system with water; start engine to pressurize; turn off engine and check for leaks.

- Most of the water can then be drained by disconnecting the engine's lower heater hose nipple and lower radiator hose.

- Reconnect everything and fill with undiluted coolant. That mixed with the residual water will provide about a 70% coolant/30% water mix. Adjust mix to taste using distilled water if more water is needed.

- Warm engine up, then check coolant level and mix when cool again.

A downside to this method is it doesn't completely drain the system of city water prior to filling. The upside is it thoroughly reverse flushes the system without the need to remove the engine or radiator drain plugs.