Free coolant pressure switch

#1

I used to have a pressure switch remoted into the block at the 12mm port that provides hot water to the throttle body. That worked fine but I always admired Jim Levie’s solution where he has a pressure sensor in the small hose between coolant reservior and radiator.

For the new car I decided to do the coolant pressure switch Jim’s way. But even trying two different 6-7psi sensors I couldn’t seem to make it work. By connecting a coolant pressure tester to the reservior I was able to figure out the problem…the coolant reservior, being connected to the system right at the very end of the pressure drop, just before the pump, doesn’t see much pressure. I did some experiments and it’s at 0psi until the tstat opens whereas it goes to 5psi.

Next I installed the pressure switch on the tstat housing using one of the 2 available ports. Note that not all tstats are drilled for 4 14mm ports, some have only the 2 for the temp senders. The extra taps are on the return hose just before it goes to the water pump so I knew it wasn’t going to be much higher pressure than the reservior, but I hoped it would be enough.

It wasn’t. And idea that I didn’t try, but would be worth trying, is to swap the pressure sensor in for the brown temp sensor on the tstat. The brown sensor goes to the dashboard temp sender and lots of folks have aftermarket temp sensors.

Then the idea hit me…rather than remoting another aftermarket pressure switch to the block like I used to have, why couldn’t I put the OEM 7psi oil pressure switch into the block instead? And, so the idea continued, I could use a spare 2 pin connector from the wiring harness to hook it up. Each of us should have 2 of these…1) OP switch 2) Gas vapor purge solenoid.

Normally one would not put a pressure sensor right on to the block, but I figure that the OEM OP sensor is designed for the environment.

I still don’t know how much coolant pressure develops in the block, but it’s more than 7psi once the tstat opens because the idea worked just fine.

#2

For those of us that have bypassed the heater core is there any reason not to put a Tee and sensor in that loop?

#3

Give it a try and see if it works. Certainly that’s before the tstat and radiator so the pressure will be higher than the 5psi at the radiator return. The pressure at the back of the head won’t be as high tho as it is at the throttle body port on the block. The pressure isn’t as high because there is a pressure drop due to flow losses as the coolant passes thru the holes in the headgasket to get to the head.

A 5 psi switch is sure to work. A 7psi switch maybe.

#4

I hope I still have my op switch because I’m going to try your idea.

#5

I put it to work today.

My 200f warning came on about lap 2 of the race today and in a few laps was up over 212. I was hoping the pressure would keep it from boiling. Right when I shifted into fourth on the backstraight lap 8 or 9 I heard a sound like when you pull the airchuck off of a valve stem. I looked down and my coolant pressure light was on. I shut it down and coasted in behind the corner station.

When I finally got towed back I found that I had only lost a liter of water and nothing had popped. Everything seams fine so I don’t understand why the light came on. With the car cold the light turns off once I reach 150-160 degrees.

#6

Looking at my logger files I hit 223f!

#7

Maybe what you heard is the pressure cap on the reservior letting go a bit.

How well is your radiator shrouded? If not so well, do better. Try to shroud it on 3 sides such that there’s no gap bigger than 1/8". Some gap on the left is ok because that pushes air towards your intake.

#8

[quote=“Ranger” post=67305]Maybe what you heard is the pressure cap on the reservior letting go a bit.

How well is your radiator shrouded? If not so well, do better. Try to shroud it on 3 sides such that there’s no gap bigger than 1/8". Some gap on the left is ok because that pushes air towards your intake.[/quote]
Shrouding is only important for fan, which in turn is only important at idle or when the car is moving slowly. At 35mph or greater the flow through the radiator is greater than what the fan can produce. At speed a shroud is actually restriction to airflow through the radiator.

@turbo329is: Since the engine overheated at speed, there is something wrong with the cooling system. My first suspicions would be the thermostat or a partially clogged radiator. I also suspect that you have a bad expansion tank cap. It should not have lifted at 223F.

#9

How hot do you guys get before giving up on a race?

#10

I was seeing OT 250 at putnam running nose to tail, but water looked good.

#11

[quote=“jlevie” post=67352][quote=“Ranger” post=67305]Maybe what you heard is the pressure cap on the reservior letting go a bit.

How well is your radiator shrouded? If not so well, do better. Try to shroud it on 3 sides such that there’s no gap bigger than 1/8". Some gap on the left is ok because that pushes air towards your intake.[/quote]
Shrouding is only important for fan, which in turn is only important at idle or when the car is moving slowly. At 35mph or greater the flow through the radiator is greater than what the fan can produce. At speed a shroud is actually restriction to airflow through the radiator.

@turbo329is: Since the engine overheated at speed, there is something wrong with the cooling system. My first suspicions would be the thermostat or a partially clogged radiator. I also suspect that you have a bad expansion tank cap. It should not have lifted at 223F.[/quote]
It sounds like you are talking about shrouding the fan and I’m talking about shrouding the radiator. That is to say, putting material in front of the radiator at bottom, right and top. Maybe a little on the left to. Jim of course knows this, but for the newbies that come across this thread down the road…Shrouding the radiator ensures that all air that hits the front of the radiator has no choice but to go thru the radiator.

#12

Hard to say for sure. Each person knows their car and has a feel for what is “right” and what is “shit, I’m done”. I have a big triple pass radiator that I shrouded carefully. If my coolant temp hit 200deg I’d know something wasn’t right.

[quote=“cosm3os” post=67354]I was seeing OT 250 at putnam running nose to tail, but water looked good.[/quote] Getting accurate oil temps can be tricky so one guy’s temps aren’t going to be another guy’s temps unless their sensors are set up exactly the same. The worst case was when I had 2 temp sensors in an oil filter sandwich adapter. Those sensors read >70deg high once the engine got good and hot.

The idea of knowing what temps are right for your car applies here too. In terms of oil breakdown conventional oil ought to take 240deg w/o a crisis and synthetics maybe 290deg. That seems high for us, but remember that oil survives in air cooled cars and turbo cars, both of which can run very high oil temps.

In terms of oil temps for my car, I take my oil temps in the pan and I don’t run an oil cooler. My oil is cooled by the air blast on the oil pan thru a big hole in my skid plate. My oil temps will vary depending on how I have that hole set up. Before the death of Old #6 my oil temps were around 190deg. In New #6 the oil is about 200deg so I need to mod the skid plate a pit to direct more air at the pan.

#13

Scott, are you talking about this port under the far right intake port? (currently has a bolt in it)

And the sensor is this single wire sensor:

Any easy way to test this sensor before I put it in? I’m assuming it’s normally closed until it’s above 0.5 bar but how to apply that out of the car? any ideas?

#14

[quote=“jlucas” post=67445]Scott, are you talking about this port under the far right intake port? (currently has a bolt in it)

And the sensor is this single wire sensor:

Any easy way to test this sensor before I put it in? I’m assuming it’s normally closed until it’s above 0.5 bar but how to apply that out of the car? any ideas?[/quote]
Yes, that’s the port.

Yes, closed below .5bar.

Why apply it out of the car? You’re on your own there.

#15

Apply it while it’s out since it’s a used part from an unknown engine, easier to deal with now than when the intake is back on.

Speaking of which when searching around for parts today. If you look at RealOEM (http://realoem.com/bmw/showparts.do?model=1113&mospid=47309&btnr=11_0119&hg=11&fg=10) it shows both 10mm and 12mm for that location (parts 13 & 14). I didn’t build this motor so it makes me wonder if I have the 10mm or 12 mm since I have no idea if there ever was a coolant pipe on this block.

Next time I’m at the shop I’ll be able to confirm.

#16

I can’t explain the 10mm reference but I’ve seen prob 3 dozen motors and they’ve all had the 12mm barb.