R6T2Corvette

Can anyone tell me for sure, which way the water flows in and out of the LS1 water pump? Does water flow from the bottom of the rad into the water pump connection at the thermostat and out of the water pump at the top and into the rad at the top? There is an argument going on at work because of the "reverse cooling" of the LS1. A friend is installing a 99 Vette engine in his hot rod and needs to know the direction that the water flows. Thanks guys.

SpeedyZ

The LS1 does not use "reverse cooling". The coolant enters at the engine at the thermostat and exits at the top. At first it is puzzling how the thermostat can control the engine temperature located at the inlet. If you look at the design of the of the thermostat the center drops into a hole in the back of the pump which is in the bypass port going to the coolant tank. That is where the thermostat picks up the water temperature.

R6T2Corvette

Thanks for the response. Looks like I am not going to win my bet at work. I thought I read an article that said that the GEN 1 Chevy small block was cooled by the coolant entering the block first, then heads, then back to the rad. The same article said that the LS1 was cooled by the water entering the heads first then the block (hense reversed cooled). This was the basis for the discussion about "which way does the water enter the rad, at the top of the rad or the bottom?"

2kbluestreak

I believe the last of the iron small blocks used in '96 Vettes was designated Gen II and had the reverse coolant flow so that the heads would be cooler allowing a higher compression ratio for more power. What apparantly worked in the lab and testing did not fair so well in real world service, so the concept was abandoned when the Gen III LS1came out.

SpeedyZ

I think you are correct, GM did play with reverse cooling on the GenII small blocks. From a performance stand point it make since to cool the heads first (reversed cooled). But from a physics stand point you always want to fill the bottom first! I think GM learned to follow the laws of physics with production engines.

VetteDrmr

The LT-1 engines ('92-'96 for C4s, '93-'97 for f-bodies) used reverse flow cooling. The theory was that the heads would be cooled first, allowing a higher compression ratio. Worked well enough, but the Gen III LS-x engines design was improved enough that they were able to go back to traditional coolant flow *and* raise CR again!

HTH, and have a good one,
Mike

R6T2Corvette

Thanks for explanation. I was so sure that the LS-x engines were reversed cooled that I bet money on it. Oh well, can't win 'em all.

SpeedyZ

Maybe you can compromise for half the money or something. Because when you see that thermostat down there on the bottom hose you sure think it would be the outlet!