Although my 4.3 was running at about 195 degrees (that's with a stock spec thermostat) and seemed pretty stable, I decided to flush the cooling system because the coolant looked rusty. After the flush, I refilled it with a50/50 mix of antifreeze and water. Now it runs hotter on the highway. The upper radiator hose is the highest point in the system, that's why I'm curious about the direction of the flow. I wonder if the coolant is flowing toward the engine from the top tank. I had always thought it went from the bottom into the engine and the hottest water exited the top and flowed into the top tank. The system is not the best design. 4 row radiator, AC condenser and a pusher fan. But it worked fine until I fixed it. Any ideas? I'm thinking of adding a coolant recovery bottle and a bleed valve at the highest point since it probably won't hurt to do so. Then I could at least be sure it's not air bound Any suggestions?
Coolant flow depends on which water pump you have on it. They can use a regular small block pump. General info is a serpentine belt set-up is reverse flow. That being said there is no outward difference on the pumps. You could be spinning the pump the wrong way.
You have the right idea of the flow out the thermostat to the radiator. If you replaced the thermostat you my want to test it if not sounds like you have some air in it.
serpentine belt systems run the pump backwards, so it has to have the correct backwards style pump on it. Normal belt systems require a normal direction pump. coolant flow is normal direction, in the bottom of the engine, out the top, like you though.
The engine is from an 89 Astro van that used a serpentine belt. I did replace the water pump before I put the engine into service and that pump was for an Astro van. Like I said, the thing had been OK until I flushed it. It will idle all day at 195 and cruise around town like that too. Anything over 60 MPH makes it start to climb. Running the heater takes it back down. I know some guys will ask if there's a spring in the lower hose to keep it from collapsing. Well I just went to check that and as I was squeezing the hose I noted that there's no spring and the hose feels strangely "crunchy", like there's some sort of crap built up in it! I will drain the system, remove the hose and report back!
My opinion is the reverse flow doesn't matter here. The reverse flow is for the engine only. I know of no modern engine that takes water from the top of the radiator and runs it thru and out the lower hose. All cars are like this, just think if it brought water in from the top if the radiator was low it would not have anything to circulate. The thermostat would never get warm if it was trying to pull cold water from the radiator. Reverses flow internally in the engine, not in the radiator.
Ok, I drained things and removed the crunchy hose and all this crunchy rust came out. I thought I was in good shape because the coolant was still looking pretty good but apparently I have a lot of crap to get rid of!
I hope it didn't plug your radiator. You might want to stick a garden hose in the lower fitting and try to flush it out or remove the radiator and flush it.
That's what I'm doing right now.. I rolled it out into the driveway and started flushing the radiator. The first few minutes was solid opaque rust water. The I took off the top hose and flushed from both there and the filler neck, more rust. I took off the upper heater hose and flushed down through the intake manifold and through the water jacket and out the bottom of the water pump, that was pretty clean, just a greenish tint of coolant and water. Next is up through the radiator from the bottom hose connection.
The question remains, do you have a serpentine belt setup on it, and the Astro pump, or do you have a conventional belt setup on it, and the Astro pump. The former is fine, if ugly and non-traditional. The latter is not acceptable. In both cases, the water moves the same way through the block. It is the pump that pumps it there differently. As has been mentioned, in both cases, in from the bottom and out the top. If you are running a reverse rotation water pump with standard belts, you are bound to have issues. You might just have an air bubble in the system. Did you remember to drill a 3/32" hole in the thermostat flange to allow air/steam to escape?
It has the Astro pump and the serpentine belt. Like I said, it worked fine till I flushed it. I have been flushing it from every hole for the past hour and it's finally running clean.Even the heater core was cruddy.
Reverse flow (Serpentine) Standard rotation (V-belt) Note the direction of the impellers. 180 degree difference
Well, I'm reporting back. I flushed for quite a while until everything was running clear no matter what direction I flushed from. I put it back together and took it out for a good long run on the highway maybe about 40 minutes or so. The temperature held perfectly! Never climbed past what I would guess was about 195 on my gauge. When I installed the gauge, I calibrated it to match the value reported by the coolant temperature sensor in the block. So although it may not be totally linear it's very accurate right at operating temperature. I also installed a piece of nylon stocking in the upper radiator hose so it will trap any more crud coming from the block. I'm really kicking myself, that engine sat on a stand for quite a few years before I installed it. Do you think I had sense enough to knock out the freeze plugs and give the block a good cleaning? It went right over my head! Sometimes I'm a dunce! Also thanks for the illustrations of the v belt and serpentine belt water pump impellers. It's good information to have for anyone who is troubleshooting a cooling problem and has no history on the vehicle.
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