Flushing the coolant and radiator question...

[OrngK5]

Hey gurus, my 78 K5 400cid is over heated the other day so I decided it was probably time to flush the coolant system again. I'm replacing the T-Stat, I am currently flushing with the chemical cleaner by Prestone, but the directions say to use only plain water and doe 3-6 hours of normal driving. Problem is I can't drive this thing without it overheating again doing normal driving around town, so I currently have it in park out front with a weight on the gas pedal at around 2000 RPMs, is this appropriate?

Second, the coolant I did drain looked very similar to the description in this thread - http://coloradok5.com/forums/showthread.php?t=282620&highlight=coolant&page=3 - in the those who have experienced this murky, brown, lake water coolant color look, how many times did you have to flush until the top of the block (where the T-Stat sits) and the coolant itself had a nice clean look to it?

Thanks a ton in advance!!

 

[Ramsdawg]

Those lil square motorS are known for over heating due to thin cylinder wall on sum blocks. But let's not go that route yet. Is this the first time it over heats? It sounds like it over heats under load. I don't think it's a cooling system issue since you have it on at 2000 rpm. When u put the prestone flush u want it to run through the whole cooling system that's why they would want u to drive it to allow the t-stat to open up and cleanse the whole system. It'll work the way ur doing it. Btw I had to flush mine two times and the last time I flushed it was with water running through my motor with the garden hose to get all that rust from the unused radiator.

 

[ryoken]

Hey gurus, my 78 K5 400cid is over heated the other day so I decided it was probably time to flush the coolant system again. I'm replacing the T-Stat, I am currently flushing with the chemical cleaner by Prestone, but the directions say to use only plain water and doe 3-6 hours of normal driving. Problem is I can't drive this thing without it overheating again doing normal driving around town, so I currently have it in park out front with a weight on the gas pedal at around 2000 RPMs, is this appropriate?

Second, the coolant I did drain looked very similar to the description in this thread - http://coloradok5.com/forums/showthread.php?t=282620&highlight=coolant&page=3 - in the those who have experienced this murky, brown, lake water coolant color look, how many times did you have to flush until the top of the block (where the T-Stat sits) and the coolant itself had a nice clean look to it?

Thanks a ton in advance!!

ya need to pull the block drains in order to do it correctly...

 

[OrngK5]

ya need to pull the block drains in order to do it correctly...

I found what looks like the bolts, or block drains, and they're next to impossible to remove. I really don't want the heads to break off either is there a secret to getting them off? I ended up driving around for a bit and sure enough the temperature skyrocketed again, the truck over heated and the water including the Prestone flush boiled over. I drained the truck again and same outcome, brown, muddy, looking lake water.

I looked in the radiator and where the T-Stat sits and it doesn't even look like this stuff touched it. When I removed the T-Stat, it had a huge buildup of this grim on it, could this build up of sediment prevent a T-Stat from working properly?

Thanks again for your help!!!

 

[British Slave]

I would try to find one of the backflush setups that go in the heater hose and wash back thru the engine to the radiator. If you have that much junk in the engine, it may be time to rod out the radiator.

 

[OrngK5]

I would try to find one of the backflush setups that go in the heater hose and wash back thru the engine to the radiator. If you have that much junk in the engine, it may be time to rod out the radiator.

What does "rod out" mean??

 

[ryoken]

I'm such a nice guy... just went and took a couple pics for ya.... here's where they are on chevys.... just above the pan, about 1/2 way down the block on each side... they are NPT plugs, not bolts... obviously mine have no plugs in them...

I don't care how many times you flush it, if your not pulling those, your not getting the sediment out of the block.... ESPECIALLY if your continuing to get lake water out... I'll bet when you pull the plugs, there's so much sediment in there, no fluid comes out... just keep poking it with a screwdriver to get it flowing...


there are other avenues than the prestone for severe cases... I use watered down muriatic acid all the time on engine blocks......

 

[British Slave]

What does "rod out" mean??

If the radiator is good enough to save, a radiator shop will remove the tanks and litterly run a flat rod thru the tubes to remove any crud. Won't work with plastic tanks. Sometimes the radiator shop can "boil" the radiator out and get the junk out.