Flush Engine Block before new radiator installed
Thread Starter
Instructor
Joined: Apr 2011
Posts: 208
Likes: 0
From: Trophy Club Texas
Flush Engine Block before new radiator installed
The coolant system on my 91 L98 was badly neglected before I bought it.
I've since flushed the system once, but it's still dirty and I need to replace the radiator.
I don't want to put the new radiator in place until the block is well flushed. I know right now there is a good amount of junk still in it. I see it caked on the inside of hoses right now.
I assume I should leave the current radiator in place and flush it a few more times before installing the new all aluminum radiator.
What are some suggestions others have to get the block cleaned out really well? I just don't want crap going through my new radiator after all the work is done.
I've since flushed the system once, but it's still dirty and I need to replace the radiator.
I don't want to put the new radiator in place until the block is well flushed. I know right now there is a good amount of junk still in it. I see it caked on the inside of hoses right now.
I assume I should leave the current radiator in place and flush it a few more times before installing the new all aluminum radiator.
What are some suggestions others have to get the block cleaned out really well? I just don't want crap going through my new radiator after all the work is done.
Melting Slicks
Joined: Jan 2009
Posts: 3,482
Likes: 196
From: folsom california
pull the knock sensors ; drain the block.
to really clean the block you'll need to pull the freeze plugs...not an easy job. BUT do pick the easiest and remove it. Inspect it carefully for rust, corrosion or pitting; if you're lucky, it will be in good shape and hopefully it indicates the rest are also in decent shape.
...if not, well time will tell, but remember that the back of the block has two freeze plugs and those require pulling the engine or pulling the transmission.
to really clean the block you'll need to pull the freeze plugs...not an easy job. BUT do pick the easiest and remove it. Inspect it carefully for rust, corrosion or pitting; if you're lucky, it will be in good shape and hopefully it indicates the rest are also in decent shape.
...if not, well time will tell, but remember that the back of the block has two freeze plugs and those require pulling the engine or pulling the transmission.
Race Director
Joined: Apr 2002
Posts: 10,036
Likes: 346
From: Anaheim CA
I just did this because of a bad experience with Dexcool (it really messed up my cooling system).
I drained all the water out of the radiator and block (remove the plugs/oil cooler lines/knock sensors or whatever is there on BOTH sides).
I replaced the coolant with plain water.
I drove the car every day and drained just the radiator every night after it cooled and filled with plain water.
I did this until the water drained out was clear and clean.
I drained the radiator and block and replaced the coolant with 50/50 antifreeze/water.
I drained all the water out of the radiator and block (remove the plugs/oil cooler lines/knock sensors or whatever is there on BOTH sides).
I replaced the coolant with plain water.
I drove the car every day and drained just the radiator every night after it cooled and filled with plain water.
I did this until the water drained out was clear and clean.
I drained the radiator and block and replaced the coolant with 50/50 antifreeze/water.
Safety Car
Joined: Nov 2008
Posts: 4,328
Likes: 15
From: Jacksonville FL
You can do a full block flush by using a PVC 3/4" male hose X 3/4" pipe thread adapter, a short length of 3/4" PVC pipe and a PVC 3/4" X 1-1/2" bushing. Assemble this and hose clamp it to the radiator hoses and a garden hose and let er rip. Do both upper and lower hoses and make sure the heater is on. Flush until clean.
Good luck!
Good luck!
Le Mans Master
Joined: May 2006
Posts: 7,708
Likes: 266
From: indy indiana
[QUOTE=Cliff Harris;1586030376]I just did this because of a bad experience with Dexcool (it really messed up my cooling system).
Me too Cliff..to the wife's car years ago. What a pia to clear the system. Happens to the best of us.
Me too Cliff..to the wife's car years ago. What a pia to clear the system. Happens to the best of us.
Team Owner
Joined: Aug 2004
Posts: 21,543
Likes: 3,216
From: Park City Utah
You guys are making this WAY too complicated.
Remove the heater core hose from the water pump. Connect to garden hose.
Remove the knock sensor on the one side, and the block drain on the other.
Turn on garden hose, let it flush out the drains until clear. Block clean, heater core flushed/clean, hoses clean. Easy.
As for dex cool...only time it makes a mess is when it's not used right. Here is my radiator after 17 years, 250k miles...
Details/story here...
http://forums.corvetteforum.com/c4-t...d-results.html
Remove the heater core hose from the water pump. Connect to garden hose.
Remove the knock sensor on the one side, and the block drain on the other.
Turn on garden hose, let it flush out the drains until clear. Block clean, heater core flushed/clean, hoses clean. Easy.
As for dex cool...only time it makes a mess is when it's not used right. Here is my radiator after 17 years, 250k miles...
Details/story here...
http://forums.corvetteforum.com/c4-t...d-results.html
Last edited by Tom400CFI; Jan 28, 2014 at 10:39 AM.
Melting Slicks
Joined: Jan 2009
Posts: 3,482
Likes: 196
From: folsom california
You guys are making this WAY too complicated.
Remove the heater core hose from the water pump. Connect to garden hose.
Remove the knock sensor on the one side, and the block drain on the other.
Turn on garden hose, let it flush out the drains until clear. Block clean, heater core flushed/clean, hoses clean. Easy.
As for dex cool...only time it makes a mess is when it's not used right. Here is my radiator after 17 years, 250k miles...
Details/story here...
http://forums.corvetteforum.com/c4-t...d-results.html
Remove the heater core hose from the water pump. Connect to garden hose.
Remove the knock sensor on the one side, and the block drain on the other.
Turn on garden hose, let it flush out the drains until clear. Block clean, heater core flushed/clean, hoses clean. Easy.
As for dex cool...only time it makes a mess is when it's not used right. Here is my radiator after 17 years, 250k miles...
Details/story here...
http://forums.corvetteforum.com/c4-t...d-results.html
my only issue with garden hoses is that water main pressure can be way above the cooling system design pressure, and if you flush through the heater core, and the seams on your 20 some year old heater core are getting weak....well you can see where this is headed. And ask me how I know.
flushing with a garden hose directly into the block and / or water pump housing eliminates possible damage to the heater core and does do an excellent job.
Team Owner
Joined: Aug 2004
Posts: 21,543
Likes: 3,216
From: Park City Utah
Well...no, I can't see where you're going with that. Two problems with what you just said;
1. Pressure is resistance to flow. If you have both drain plugs out of the block, and the radiator is out (meaning the lower radiator hose is off)...where is the resistance to flow? No way you're going to build 10 PSI+ of pressure unless you are thinking about a FIRE hose...and not a garden hose!
2. Ya gotta flush the heater core. Sorry, but it's a haven for crud to collect in, and if you are flushing the cooling SYSTEM...well, the heater core is a significant part of that too.
Using the method that I outlined, you don't need to build adapters, run the engine and drain multiple times, freeze plugs (?) etc. Ya just stick a hose on/in the end of the heater hose, run until it flows clean, and you're done. Takes about 60 seconds + removing, installing the sensor/drains.
1. Pressure is resistance to flow. If you have both drain plugs out of the block, and the radiator is out (meaning the lower radiator hose is off)...where is the resistance to flow? No way you're going to build 10 PSI+ of pressure unless you are thinking about a FIRE hose...and not a garden hose!
2. Ya gotta flush the heater core. Sorry, but it's a haven for crud to collect in, and if you are flushing the cooling SYSTEM...well, the heater core is a significant part of that too.
Using the method that I outlined, you don't need to build adapters, run the engine and drain multiple times, freeze plugs (?) etc. Ya just stick a hose on/in the end of the heater hose, run until it flows clean, and you're done. Takes about 60 seconds + removing, installing the sensor/drains.
Last edited by Tom400CFI; Jan 28, 2014 at 08:53 PM.
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Melting Slicks
Joined: Jan 2009
Posts: 3,482
Likes: 196
From: folsom california
Okay. Had no heat due to what I suspected was a clogged heater core. Got a Prestone flush kit and throughly flushed the heater core; there was an improvement in heat output but I now had a leaking heater core; when the heater core was replaced found a seam failure in the original heater core. This was in a 2001 Ford pickup.
I'm just saying that the heater core has to accept whatever pressure is being introduced into it, say 60 psi water main pressure, and even with all the downstream items like radiator hoses, caps, etc. removed, there is still considerable pressure build up in the heater core before the fluid leaves the heater core and experiences any significant pressure drop.
OF COURSE millions of cooling system have been flushed through the heater core without the heater core failing, but seriously, to do the through cooling system you are contemplating, I would hook up directly to the hoses leading to/from the thermostat housing/ water pump and flush it for an extended period of time, whatever is necessary. After thats been flushed clear, then gently backflush the heater core for only as long as needed.
moral of story? be gentle. heater core replacements are not fun. good luck.
I'm just saying that the heater core has to accept whatever pressure is being introduced into it, say 60 psi water main pressure, and even with all the downstream items like radiator hoses, caps, etc. removed, there is still considerable pressure build up in the heater core before the fluid leaves the heater core and experiences any significant pressure drop.
OF COURSE millions of cooling system have been flushed through the heater core without the heater core failing, but seriously, to do the through cooling system you are contemplating, I would hook up directly to the hoses leading to/from the thermostat housing/ water pump and flush it for an extended period of time, whatever is necessary. After thats been flushed clear, then gently backflush the heater core for only as long as needed.
moral of story? be gentle. heater core replacements are not fun. good luck.
Last edited by mtwoolford; Jan 28, 2014 at 08:15 PM.
Max G’s
Joined: Nov 2008
Posts: 2,751
Likes: 79
From: Monroe OH
NCM Sinkhole Donor
If you are wanting to get the complete system cleaned of build up, drain coolant, pour in about a cup of laundry detergent, powder, then fill with water. If you don't want it thought the heater core then bypass it. Run that thought the car for 30-45 minutes. Open drain valve on radiator and remove surge tank cap run water through engine until get just clear water.
Team Owner
Joined: Aug 2004
Posts: 21,543
Likes: 3,216
From: Park City Utah
Fair enough. I guess my feeling is that if you have no resistance to flow (drains open, hoses off), and you're popping heater cores, then you needed a new core anyway. I've done the process I described above many, many times and never a heater core issue have I experienced. Also you know...the valve on the garden hose is adjustable too. 
Safety Car
Joined: Nov 2008
Posts: 4,328
Likes: 15
From: Jacksonville FL
Yes I didnt mention that you dont want to turn the hose bibb on full force if you doubt your system. Cliff's method of going from the bottom to the top is a good idea as well.
As far as pressure building in the block, the 3/8" hole (or 2) isnt enough to stop pressure from building. It will decrease but it will be much more than 10psi assuming 60psi in. That being said, I flushed mine using the 1-1/2" radiator hoses so the larger opening was adequate to keep the pressure from going above safe levels. Having the larger opening was a good thing in my case as a piece of spring from the inside of an old hose washed out.
As far as pressure building in the block, the 3/8" hole (or 2) isnt enough to stop pressure from building. It will decrease but it will be much more than 10psi assuming 60psi in. That being said, I flushed mine using the 1-1/2" radiator hoses so the larger opening was adequate to keep the pressure from going above safe levels. Having the larger opening was a good thing in my case as a piece of spring from the inside of an old hose washed out.
Melting Slicks
Joined: Aug 2008
Posts: 2,082
Likes: 50
From: Palmdale CA
if your hell bent on doing a high volume water flush, then do it from the Top down. In order to do this you will have to remove the thermostat and reinstall the thermostat housing with out it. Remove both upper and lower radiator hose's, and shove a garden hose down it's throat and let it rip, this allows a lot of crap to be carried out of the water pump..
Drain the remaining water and re fill..
Drain the remaining water and re fill..
Team Owner
Joined: Aug 2004
Posts: 21,543
Likes: 3,216
From: Park City Utah
^That works too...but "misses" the heater core.
That's not right for three reasons;
1. you actually have two holes open; a vlock drain on EACH side of the block.
2. The drain holes are really ~1/2 inch
3. Here is the big one...the lower radiator hose is off. That is about a 1.5" hole...and can out flow your garden hose any day of the week.
1. you actually have two holes open; a vlock drain on EACH side of the block.
2. The drain holes are really ~1/2 inch
3. Here is the big one...the lower radiator hose is off. That is about a 1.5" hole...and can out flow your garden hose any day of the week.
Last edited by Tom400CFI; Jan 29, 2014 at 08:21 AM.