Cooling system help - leaking out of the cap?

Having trouble w/ the cooling system - everything is good until the digidash reads 181* (taken from the passenger head location) .... at that point coolant starts leaking past my radiator cap. I assume that's around the point when the thermostat begins to open (stock 195* t-stat)

I have a 1.5qt. canton on the passenger beam, the highest point in the system. I have it filled 1/2 way up



The -4 hose goes to the coolant bleed pipe on the engine
The 90* -8 hose on the back goes to the radiator top ports (it T's at the radiator and goes to both of the ports)

The -6 startlite hose goes down, under the crossbeam, then to a puke can on the passenger frame rail, filling from the bottom (which then vents to the ground from the top)



I also have a -10 hose from the bottom of my canton tank to a fitting on the stainless pipe that goes from the passenger side of the engine (after t-stat) to the lower passenger side of the radiator.



Also have the waterpump inlet and outlet hoses looped together.


When coolant comes leaking out of the cap my puke can is empty, so I can't figure out why, at 181* always (e.g., if digidash reads 176 it's leak free) coolant comes out of the cap. I'm thinking:

- bad cap (stant 16lb)
- I should be feeding teh bottom of the Canton tank to the driver side stainless pipe, not the passenger side (although I'm pretty sure this is incorrect)
- Canton reservoir is too small and when t-stat opens it fills up to the top and past the cap
- Instead of feeding the canton tank directly to the passenger pipe I should feed it to one of the heater connections (heater in/out) and plug the other?

Okay, that was stupid of me - I just didn't have the cap on tight ... because of the location I have to almost stand in the engine bay to fully get it seated, trying to do it from an angle outside the car is no beuno :O

Yes, I probably shouldn't be building cars that go on the road, stop laughing

That's okay Alex. I changed oil one time and forgot to replace the drain plug! What a mess!

molleur said:

That's okay Alex. I changed oil one time and forgot to replace the drain plug! What a mess!

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I've got that tied - on my cobra the oil temp sender (in the pan) went out so I figured that since the sender was at the top of the pan, if I removed it (full of oil), maybe only a little it would leak out and I could quickly swap in the new sender.

Um, yea, needless to say that didn't work out. At all

Builders Bloopers

When I fired up the motor in my FFR '33 Hot Rod for the first time, I forgot to loop the Automatic transmission lines together. I was so excited that it actually started, I didn't notice the red AT fluid pumping out the front like a punctured Aorta artery. My driveway looked like there had been a bloody knife fight. What a mess! It quickly emptied the AT pan, but fortunately I shut it down before there was any internal damage.

Alex, do you get the feeling we've all had our "Builders Bloopers"?

Re: Builders Bloopers

rumbles said:

Alex, do you get the feeling we've all had our "Builders Bloopers"?

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It's what makes the journey so much fun =)

Although now I've got anoter coolant mystery - the GM ecu operates fom the front drive side head. I've got my water temp sender for the digidash in the passenger rear head. That location reads 20* cooler than driver front ..... I was staring at my water temp wondering why it never got about 188, and yet my coolant hose was hard at the t-stat and the fans were on. Then I remembered reading how the rear port runs a lot cooler than driver.

Mmmmm; I'm thinking I have 2 options (don't want to drill & tap the water pump) .... either modify the driver front fitting so it uses both GM and digidash senders, or make a ] fitting that goes between the heater in and heater out hoses (which I have looped together at the moment) and put the water temp sender there.

Interesting, Will Campbell and I were just discussing if we could use that passenger side bung for a dash temp gauge sender.

Did you actually measure the -20 degree temp difference in the Passenger bung?

I wonder if there is such a thing as a T-fitting for the drivers side bung that would allow you to screw in both the ECU temp sensor and a dash gauge temp sensor?

rumbles said:

Interesting, Will Campbell and I were just discussing if we could use that passenger side bung for a dash temp gauge sender.

Did you actually measure the -20 degree temp difference in the Passenger bung?

I wonder if there is such a thing as a T-fitting for the drivers side bung that would allow you to screw in both the ECU temp sensor and a dash gauge temp sensor?

Click to expand...

I didn't measure it directly, but I can see the problem.

My t-stat is 195*. When my digidash reads 175 the lower rad hose is hard and the t-stat is fully open

The GM ecu has fans on at 205*. When my digidash reads 180 the fans are off. When the digidash reads 185* the fans pop on

So either my digidash reads 20* lower just for the fun of it, or the rear passenger port is 20* lower than the driver front. Given I've read the passenger rear port reads lower tan the drive front, I'd believe it.


I believe the ports are M16x1.5 (have to check) ..... if a T doesn't exist in the aftermarket world to let both GM ECU sensor and a 1/8'' npt sensor run off the driver front, I'd gladly pay to have somebody machine one.........

The port thread size for the water temp sensor in the cylinder heads is M12x1.5.

The port thread size for the oil pressure sensor in the valley cover is M16x1.5