Hi,

The coolant in my GT2554r always starts boiling when I switch the engine off. Even if I drive carefully and slowly to let everything cool down the last kilometers. I was wondering if it makes sense to put a small pump in the feed line, which switches on when I switch the engine off and runs for a few more minutes. I hope to find a pump which allows the regular flow to be pushed through by the car's system when the engine is running, so it only needs to kick in after shutdown. What do you guys think?

Cheers,

Hugo

 

Same thing happens on my 2560 setup. I'm pretty sure that's the reason turbo timers exist. I'm relatively new the to the turbo world, but I believe it's normal, the turbo holds a lot of heat.

 

Same behavior here on my 2560. It's normal and I haven't had an issue in a year and a half. The heat from the turbo results in thermal siphoning and circulates coolant through the system on its own. There's a definite benefit to having an auxiliary coolant pump running on a timer after engine shutoff, but it's not necessary enough that many people run them on our setups.

 

I've looked at the turbo timer, but it doesn't cover this problem. I think it is useful when you stop the engine directly after thrashing about. But I cool down the engine first, let everything settle and then switch off. [nerd-mode] my coolant cap is rated at 1,3 bar, water (coolant) boils way below 200 degrees Celsius. No matter how careful I cool the car down, the hot end of the turbo will never be below that when I switch it off. [/nerd-mode]

And, truth be told, I like overengineering things. It's a hobby for me. So I think I will look into a pump with a bypass valve. Valve normally open when the engine is in use, and the valve and pump powered for w few minutes after shut-down.

Hugo

 

As stated previously, that is normal and there is really plenty of flow from cool towards hot as the coolant absorbs heat from the turbo. The coolant keeps flowing after the engine is off. The purpose for water cooling a turbo is specifically to keep the oil temperature below 280° or so. If the coolant boils at 220° Fahrenheit and is continuing to circulate there are no worries for oil breakdown inside the turbo. Early turbos were oil cooled only and would have bearing failures as a result of hot shutdowns. With the addition of water cooling, turbos last very very long time.

 

Fair enough, I'll be interested to see what you come up with!

 

And how would that happen?

Cheers,

Hugo

 

Heat rises.

 

It does, because the cooler liquid has a higher density then the warmer liquid. As long as it stays in the same phase and has somewhere to rise to. In this case, the liquid is boiled to a gas which has a lower density then the liquid, period. And that gas will always stay on top of the liquid. Hence, once the boiling has started, the flow due to temperature difference stops. So the flow of coolant stops.

Hugo

 

Thermal siphoning in turbochargers exists. End of story.

 

 

Ah, so we just ditch science and yell something unfounded. Sorry, I'll pass.

@douginjenison; thanks, that helps. I'll have a look at my high-mount Kraken set-up, I fear the outlet of the turbo is above the port it connects to. If it isn't, I'll try the rotation-trick as described.

Cheers,

Hugo

 

No, he is correct - I was just adding more info in the case that someone had a question on routing and positioning.

"However, an additional phenomenon known as “thermal siphoning” pulls water through the turbo’s center housing if the water lines are properly routed, even after the engine is shut off and the water pump is no longer pumping." -Garrett

https://www.garrettmotion.com/racing...or-your-turbo/

 

If the flow-route allows, yes. In case of the high-mount I have (I just checked), the return to the engine is a lot lower than the exit on the turbo. So, gas from boiling will collect at the highest point and stay there, stopping flow. Hence, (back to the subject), I need to keep it flowing with a pump or something similar.

I can also put an electric motor on the original waterpump with a PID control. This can do it's job during engine use, and keep running a bit after shut-down.

Hugo

 

Not yelling. Apologies, I didn't mean to come off as a dick. I'm interested to see what you rig up and what your findings are.

 

I believe some cars have small electric water pumps to circulate water through turbos after shutdown. Mercedes/BMW both have this I believe.

 

All ~2020 and up gas engine Ford vehicles now have auxiliary electric coolant pumps. However, they're for HVAC purposes only, they only run to circulate coolant through the heater core when the engine is automatically shut off at stoplights.

Just a data point, nothing more. Weird to me that they don't run them after shutoff on the turbo cars. It'd be super easy to have the pump on a timer after engine shutoff depending on engine runtime and CLT.

 

@HugoW I would like to take a step back for a second with a 'stupid question'. How do you know your coolant is boiling? Are you getting fluid out of your coolant overflow during these shutdowns? Have you verified your 1.3bar pressure cap is in working order?

 

Yes. I have no coolant flow-back in to the tank during engine opertation. A few seconds after shut-down, the turbo sounds like the kettle is on for tea and the overflow opens a few seconds later. I have two caps (one on the radiator, which has a blocked overflow port) and one in the reroute line (highest point, with overflow to the tank). Switching caps (yes, I tried) gives the same result and both caps were bought about a year ago when I re-did most of the cooling system. Either they are both defective, but my guess is they both work.

Hugo

 

I can hear mine boiling sometimes. My turbo is mid mount so it certainly siphons properly.

I still believe that cooler coolant from the mixing manifold area will flow to the turbo and then to the head after the turbo as there is a difference in temperature between those two areas, the mixing manifold and the head.