I was wondering if anybody has run across this before. I have a 6.0 liter with a borg 475, I am logging coolant pressure and it has been going up and down on the data logs just normal driving it. I thought it may be due to the fact that I do not have heater hoses on it and the water pump blocked off. Not looped. So I drained the coolant and drilled a hole in the thermostat and it is doing the same thing. I am on holley efi, but it is not from the thermostat cycling. Every time the fan comes on the pressure drops to zero and then when the fan shuts off it starts to build pressure. Pressure sensor in adapter blocks between the water pump and block. Coolant temperature sensor in stock location, cylinder head. Any insight would be greatly appreciated. I do not have wot data yet. I have a couple of log files but it wont allow me too attach them.

 

It is seeing the charge pressure of the block if you are talking about it moving vs RPM
it is a very poor place to take a reading.

Just post a screen shot

 

And yes the system will drop almost vertically when the temperature drops. It is a sealed system and you can't compress water


​​​​​​This makes the system hyper sensitive to any even very small change in system temperature, and anything else for that matter

This is why I run a small amount of air in the degassing tank. This gives you some compressible volume to stabalize the system

 

The highest temp you hit is the reset point .... You hit 190 you are at cap pressure.....

It cools to 180 the pressure drops.... You need to return to 190 to hit cap pressure again

Then it gets to 200.... That is the new set point.... If it cools from there... It would have to get to 200 now to hit cap pressure again

 

Thanks for the reply but I had the cap off of it and had my stant pressure tester on it. so it would relieve on cap pressure because that is what I thought also. I just found it weird that it was dropping to zero every time the fan would kick on no matter how hot it was. Where would be the best place to take the pressure. I do not have a surge tank.

 

Highest point in the cooling system farthest from the water pump inlet or outlets. This will give you the most stable system pressure measurement while letting you know when pressure spikes due to head lifting/gasket leak.

 

Put in the radiator. I see around 10-12psi normal driving and 14 at wot.

 

Thanks everyone with the replies. Badass68 does your coolant pressure drop off to zero at all while you are driving and how did you mount it in the radiator.

 

I would loop the hoses . This supplies coolant to rear of thermostat. I've been thru this

 

Yep, good way to burn up the pump and cavitation the pump blades to death. They don't cycle coolant right with them blocked. I recall a thread around here last year on this subject and his thermostat wouldn't function correctly.

 

I thought they needed to be looped vs blocked? I actually thought I heard gm built that loop hose for the c5r cars. Can you expand on this? I am going to search for the thread.

Or is that what your saying?

 

I blocked mine. I had no room for a loop.
I also drilled a 3/8” hole inside the pump itself to allow it to function as if it had a loop. Or heater lines.

I don’t measure coolant pressure.
0 issues with temp control.

 

i drilled a small hole in mine as well.

Seems it helped with thermostat operation as there is a bit of flow across the stat even when it’s closed, making it open and shut more consistently.

 

I'm pretty darn sure you don't loop the holes. I'd like to see where this information is coming from? Sounds bogus.

The pressure differential from the 2 lines is what causes coolant to flow through the heater core. If you have no heater core the lines should be blocked. Race blocks come from GM with these blocked and retain them blocked on the circuit from what i've seen. Having the hoses looped is allowing cross flow from low to high side of the system and would be counter productive at cooling, dropping cooling efficiency. It most defiantly won't burn up a water pump, as I've run about 10 engines this way with no troubles. Including my current vehicles.

 

Thanks again everyone for the replys. I did alot of research on this before I plugged them. I know a lot of guys are running them lopped with no problems but I was under the same impression what force fed is saying. Thanks for the diagram force fed, does any have a flow diagram of the water pump. One thing I noticed today is that the thermostat I had in it was a mr gasket thermostat and the metal piece on the back of the thermostat where it forces to bypass coolant into the heater core when the thermostat is closed has 4 holes drilled in it that are about 1/8 inch each. After giving this some thought, lopping the hoses would be the same thing as putting the hoses to a heater core.

 

It really isn't the same at all. The heater core acts as a big restriction between the high and low sides. There is also an additional restrictor in the heater core line. With a loop there is open flow between the two, making the system less efficient. As far as I know, and until someone can explain differently... it's not a good idea to loop the lines.

 

Heater core should not create too much restriction. Although slightly more than 6" looped hose. Any idea which LS vehicles run heater hose restrictors? I've not seem one on trucks/suvs. I'd assume restrictor located in supply hose (smaller hose)?

 

Believe the LS1's did? aren't they routed to the surge tank in the trucks?

 

I see on the restriction in the heater core, So I thought I was on to something today but it ended up the same way. I am not running a surge tank, I am running an overflow bottle, so i pulled the fitting out of the top of it and it did not have a dip tube on it, so i put one on remounted it vertical and and filled it up. I still have the heater hoses blocked off with pipe plugs and it still do the same thing. One thing that puzzles me is that when it starts up cold it will build pressure to the cap release, you can watch the thermostat open (180) on the temp read out, all the way until low speed fan comes on at 205. As soon as the fan comes on it drops all the way to zero. You can squeeze the radiator hose and it is soft. If you take the cap off you can watch the coolant rise and fall with the fans cycling on and off. I am surprised how far it is dropping in the radiator, like 2 inches. It is not low on antifreeze, I pulled the cap when it is cold and the radiator is plum full to the neck. I was just surprised how far the coolant is changing levels in the radiator.

 

I'd get a burp funnel on it and make sure you have all the air out. If I top off my system, at operating temp the "burp funnel" is damn near full. Coolant level rises a TON. I've always had a lot of air in my LS motors. They are notoriously hard to "burp".