all black 4G63
5+ Year Contributor
- 276
- 50
- Aug 5, 2019
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Chicago,
Illinois
(Long thread warning )
So I wanted to post this as more of an informational/discussion thread based on coolant pressure monitoring on a 6 bolt motor. I’m doing this because I couldn’t seem to find any solid “answers” or info on-line other than researching fluid dynamics and running into the issues I was having. “I’m sorry if this is blatantly obvious to everyone already as i was second guessing myself.”
So when it comes to monitoring coolant pressure in your engine we do this to verify how much boost is “too much” as the cylinder head may lift and combustion pressures may push into the coolant chamber which at that point can damages heads gaskets and more.
So I’m running a non O-ringed block with EVO MLS and L-19 studs on a PTE 62/66, e85 @35 psi. Haltech 1500 NSP. Makes little over 600hp
I started monitoring coolant pressure at the port designated for the IPC coolant gauge on the lower side of the thermostat housing (1/8” bspt). I was running the Haltech Bosch coolant temp/pressure sensor. I have no heater core or coolant running to the throttle body.
During warm up-idle everything was normal, low coolant pressure and temp. At around 190F ~1000 rpm pressure was 13-14psi and the t-stat would open. However, if I rev up the motor (5000 RPM +) coolant pressure would easily reach 40-50psi! This was crazy because I thought I had a severely damaged motor, but I would never push coolant or overheat.. also during hard 35 psi pulls I would also reach 40-50psi.
I began to think having the Bosch sensor mounted on the motor (t-stat housing) was vibrating throwing the readings off. So I bought the Haltech 150psi TI pressure sensor and remotely mounted it on the fire wall even using rubber washers as a precaution. This made absolutely no difference, I would still reach 40-50 psi reving at an idle.
At this point I was starting to think that I didn’t fully understand what was going on so I had to dig further. I knew there was no way I had that bad of a motor especially since the gasket was fairly new and compression was good and I didn’t loose coolant or overheat.
Looking on-line learning that everyone would say coolant pressure shouldn’t go too far over cap pressure spec (.9 Bar 13 psi) I thought maybe I didn’t fully understand the cooling system of these 4G’s..
Basically during warm up (t-stat) closed the coolant obviously needs to flow and is bypassing the radiator (like normal bypass). If you look at a 6 bolt block there are two ports at the water pump mount this would technically be where “bypass” would take place. Obviously when the system is in “bypass” mode (t-stat) closed the centrifugal pump is producing pressure and flow pushing coolant through the block and head. While the t-stat is closed the coolant circulates back to the pump from one of the two ports at the pump mount on the block. Since the centrifugal pump design is to disperse fluid on the outside of the impellers the pressure will constantly increase as the RPMs increase. Stock DSM pumps produce max. 140 Lit. @ 6000 rpm. That’s a lot if you think about it. So how does this work? How could I see 40-50 psi if the system is supposed to be under 13psi.
Well it’s not. If you use the laws of fluid dynamics and Bernoulli’s principle that the pressure of a flowing liquid will change based on the change in the diameter or area of a pipe. Basically, the area “pre t-stat” is larger then “post t-stat (radiator side)”. So naturally what will happen when the pressure behind the t-stat is high and is building it will drop when the t-stat opens. (this is because the area behind the cap is larger then the diameter of the piping on the rad side). This is the same as holding your thumb over the end of a garden hose. The flow will not change (Bernoulli’s principle) but the pressure will and in this case it drops.
Centrifugal pumps can actually build so much pressure that when the cooling system is in bypass and if there’s not enough of fluid at the center, the pump can cavitate and produce and area of air. You may notice this if you boost hard with slightly low coolant levels you will see your coolant temp rise suddenly then drop when off the throttle.
So based on this info I moved the coolant pressure sensor to the port where the AC temp sensor would’ve normally been (see photo). Now at an idle and during hard boost I barely reach over 15psi.
I hope this will be the correct way to monitor coolant pressure as I would think if the area past the t-stat would build under boost this would be an accurate way to tell if combustion pressure is leaking in.
Please let me know your thought or if I’m just crazy and over thinking this but, hey at least I know my motor and head gasket are good I guess.
So I wanted to post this as more of an informational/discussion thread based on coolant pressure monitoring on a 6 bolt motor. I’m doing this because I couldn’t seem to find any solid “answers” or info on-line other than researching fluid dynamics and running into the issues I was having. “I’m sorry if this is blatantly obvious to everyone already as i was second guessing myself.”
So when it comes to monitoring coolant pressure in your engine we do this to verify how much boost is “too much” as the cylinder head may lift and combustion pressures may push into the coolant chamber which at that point can damages heads gaskets and more.
So I’m running a non O-ringed block with EVO MLS and L-19 studs on a PTE 62/66, e85 @35 psi. Haltech 1500 NSP. Makes little over 600hp
I started monitoring coolant pressure at the port designated for the IPC coolant gauge on the lower side of the thermostat housing (1/8” bspt). I was running the Haltech Bosch coolant temp/pressure sensor. I have no heater core or coolant running to the throttle body.
During warm up-idle everything was normal, low coolant pressure and temp. At around 190F ~1000 rpm pressure was 13-14psi and the t-stat would open. However, if I rev up the motor (5000 RPM +) coolant pressure would easily reach 40-50psi! This was crazy because I thought I had a severely damaged motor, but I would never push coolant or overheat.. also during hard 35 psi pulls I would also reach 40-50psi.
I began to think having the Bosch sensor mounted on the motor (t-stat housing) was vibrating throwing the readings off. So I bought the Haltech 150psi TI pressure sensor and remotely mounted it on the fire wall even using rubber washers as a precaution. This made absolutely no difference, I would still reach 40-50 psi reving at an idle.
At this point I was starting to think that I didn’t fully understand what was going on so I had to dig further. I knew there was no way I had that bad of a motor especially since the gasket was fairly new and compression was good and I didn’t loose coolant or overheat.
Looking on-line learning that everyone would say coolant pressure shouldn’t go too far over cap pressure spec (.9 Bar 13 psi) I thought maybe I didn’t fully understand the cooling system of these 4G’s..
Basically during warm up (t-stat) closed the coolant obviously needs to flow and is bypassing the radiator (like normal bypass). If you look at a 6 bolt block there are two ports at the water pump mount this would technically be where “bypass” would take place. Obviously when the system is in “bypass” mode (t-stat) closed the centrifugal pump is producing pressure and flow pushing coolant through the block and head. While the t-stat is closed the coolant circulates back to the pump from one of the two ports at the pump mount on the block. Since the centrifugal pump design is to disperse fluid on the outside of the impellers the pressure will constantly increase as the RPMs increase. Stock DSM pumps produce max. 140 Lit. @ 6000 rpm. That’s a lot if you think about it. So how does this work? How could I see 40-50 psi if the system is supposed to be under 13psi.
Well it’s not. If you use the laws of fluid dynamics and Bernoulli’s principle that the pressure of a flowing liquid will change based on the change in the diameter or area of a pipe. Basically, the area “pre t-stat” is larger then “post t-stat (radiator side)”. So naturally what will happen when the pressure behind the t-stat is high and is building it will drop when the t-stat opens. (this is because the area behind the cap is larger then the diameter of the piping on the rad side). This is the same as holding your thumb over the end of a garden hose. The flow will not change (Bernoulli’s principle) but the pressure will and in this case it drops.
Centrifugal pumps can actually build so much pressure that when the cooling system is in bypass and if there’s not enough of fluid at the center, the pump can cavitate and produce and area of air. You may notice this if you boost hard with slightly low coolant levels you will see your coolant temp rise suddenly then drop when off the throttle.
So based on this info I moved the coolant pressure sensor to the port where the AC temp sensor would’ve normally been (see photo). Now at an idle and during hard boost I barely reach over 15psi.
I hope this will be the correct way to monitor coolant pressure as I would think if the area past the t-stat would build under boost this would be an accurate way to tell if combustion pressure is leaking in.
Please let me know your thought or if I’m just crazy and over thinking this but, hey at least I know my motor and head gasket are good I guess.
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. I've ballooned a radiator before so when it goes real bad, I know it's way more than 40 psi.
