SBC coolant purge solution

workingdog

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I've been posting a lot of questions lately, since I just took delivery of my '84 FJ60 from Valley Hybrids 2 weeks ago, so I thought I post a solution I found to an overheating problem with the 2005 5.3l Georg installed.

The FJ60 had run like a top, except for a small wiring problem, until a couple of days ago, when it began to go into limp mode due to overheating. This problem was complicated by the fact that the temp gauge wasn't working so it took a scan gauge to figure out what was happening. The temp was wandering between 220 and 269 when it would go into limp mode. Georg suspected the temp sensor, so I replaced that but the problem only got worse and I was now noticing a lot of coolant leaking from the rear seat heater - but not enough that I couldn't keep ahead of it by keeping the expansion tank full.

I bypassed the rear seat heater and filled everything back up, but the truck was now overheating in less than two miles with full radiator and full expansion tank. I had purchased and was about to install a new thermostat when I did some searching on Google. Based on what I found, I pulled off the top radiator hose and stuffed the hose down it. It ran for quite a while, much longer than required to fill the house. I hooked it back up and my problem was mostly solved.

The thing it took me a while to figure out is that these cooling systems are backwards from old school SBCs. The thermostat is on the bottom hose and the water pump has to have enough water in the block to prime it - no matter who much water is in the radiator and expansion tank.

Here's what I think happened. All this occurred when I started to use the heaters. I think there was air in the primary heater coil that got into the system and the bad rear seat heater core allowed more air into the system. Just enough for the water pump to go dry and not be able to prime itself. Full radiator, full expansion tank, but with an unprimed pump, no coolant is moving and the truck heats up almost immediately.

I'm still going to replace the thermostat, because the truck is running steadily between 215 and 230 - which is a little higher than I'd like. I'm also going to install one of those flush T's into the upper radiator line that will allow me to fill the radiator from the top of the upper hose.

Peter
 
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Plano texas
Id agree. A GOOD flush should take a while. I flush the front and back heaters and make sure when I replace with distilled H2O THAT THE HEATERS ARE BOTH ON. Good job. MIke
 
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just a note...on the SBC 5.7 Vortec .

When and if I have to refill the cooling system I use to add coolant to the radiator and little by little would be able to bleed the air our ot fhe system. Due to the relationship of the radiator and the engine vehicle is prone to air pockets.

So what I do...is just take the thermostat water neck loose from the intake manifold, then take the thermostat out, and fill up the coolant at this point, replace items I removed and then fill up radiator. This makes getting the ir pockets out so much easier.

We found out that literally the engine could be very low on coolant while the radiator shows full, even after running the engine for short periods to get the thermostat to cycle. Was seeing large spikes in teh coolant temp readings and then decidied to make sure thermostat was working and when we removed thermostat it was obvious that engine was not full. Dont' know if this is unique to the 5.7 Vortec as it has a bypass hose configuration on the water pump.

I just run the primary heater and do not use the passenger heater if that makes any difference. I just have heater hose runnning to supply the primary heater and that's all.
 

orangefj45

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norcal
the 2nd gen and later model vortecs are definetly a little trickier to "fill" with coolant than all the other Gm V8s.
in peter's case i ran the front heater but neglected to run the rear. i usually always run both heaters after any coolant ralated work has been performed on a cruiser, no matter what engine is in it.
for the later vortecs, i have a special funnel kit made by lisle that allows you to store an extra quart and a half in the fnnel so the coolant can work it's way into the engine. the kit isn't expensive, about $30 and works well. you have to let the engine run for a while. i usually let the funnel do it's thing overnight before starting a later vortec.....

post some pics peter!
 
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Dec 18, 2010
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FT. MYERS FLA
airlift coolant fill tool

i purchased one of these when i worked at bmw and have never questioned if i have air in the system since. i hook my shop air to it and it draw 30" of vacuum on the system then i hook up the fill hose stick it into my coolant suppy and it fills the system full the first time every time. if you cant pull 30" of vac or it drops after you close the valve you have a leak well worth the $100 they cost Airlift Cooling System Leak Checker and Airlock Purge Tool Kit#
 

workingdog

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I totally need that! A little more sophisticated than jacking it up 2 feet and trying to made a garden hose to the upper radiator hose.

Peter
 

rover67

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Sep 5, 2006
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Boulder, Co
they are harder to fill than other vehicles I have worked on. Typically I let it idle till it gets hot, then shut it down and let it cool. it'll suck coolant in as it cools. refill overflow and repeat.

I also installed a purge valve in my upper rad hose, it helped get the air out as well. I have also heard that the steam vent lines from the heads help vent the air as well. I have my steam vent hooked to my upper rad hose also, though there are many ways to do it.

FWIW, I have a 190 deg. thermostat in mine and it runs at that temp... stock rad, GM mechanical fan, decent shroud.

that vacuum thinggie euro posted looks cool too.
 

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