cooling woes

[82eye]

been having cooling issues ever since i built the engine.

for the longest time the car refused to bleed proper. when it finally settled, the heater core and heater core pipe o-rings gave out a couple 100km later. the core developed a small leak, and the o-rings had plasticized and would no longer hold pressure.

replaced the core and o-rings, re-bled the system and all was good. then i took the car on a 700km trip and it threw a low coolant check just as i was getting home. the res was near dry.

oil checks good, no milkshake under the cap, and it was clean and even a touch low in the pan. every single hose is new, no leaks. i'm getting frustrated with it. added coolant and it went through a little over 2 days of short trip city driving. it's not the main car so not many miles.

my best dart toss is maybe the expansion tank or rad developing a leak, but it's a flat guess. called around for a pressure test and decided to try a cheap test kit myself for the price.

anyone have any ideas they can toss in?

[MrBurgundy]

Sometimes there is air trapped and it will eventually make its way up to the tank in exchange for water, so the level will drop.

If you have a leak, just run the car, and it will build pressure naturally. I don't think there's a need for a DIY pressure tester. But same time, it wont hurt.

M20s are waffleswaffleswaffleswaffless sometimes when it comes to bleeding. Also, when you bleed these cars after a heater core leak, make sure the HVAC is switched to heat which actuates the heater valve.

If it's not then water will never make it down into the dash.

So you added after the low coolant trip, then it was triggered again, correct???

It's either remaining air thats trapped, a leak at the core you just did or a leak you haven't found under the good yet...

Run the car at home. If there's a leak, you're gonna see it on the carpet or the driveway. make sure the heater is on too when you do this.

[82eye]

Sometimes there is air trapped and it will eventually make its way up to the tank in exchange for water, so the level will drop.

If you have a leak, just run the car, and it will build pressure naturally. I don't think there's a need for a DIY pressure tester. But same time, it wont hurt.

M20s are waffleswaffleswaffleswaffless sometimes when it comes to bleeding. Also, when you bleed these cars after a heater core leak, make sure the HVAC is switched to heat which actuates the heater valve.

If it's not then water will never make it down into the dash.

it's got great heat, pretty sure the heater core is circulating. there's no warm water on the drivers side footwell, so the valve and heater tubes should be holding.

So you added after the low coolant trip, then it was triggered again, correct???

didn't trigger the second time but was a little low when checked. could've been trapped air from the first low trigger

It's either remaining air thats trapped, a leak at the core you just did or a leak you haven't found under the good yet...

Run the car at home. If there's a leak, you're gonna see it on the carpet or the driveway. make sure the heater is on too when you do this.

have tried. everything remains dry. it seems to only lose coolant when moving.

we're guessing the expansion tank cap may have jammed. it's supposed to let loose at 1.4 bar. in 1997 there was a recall on the caps as the valve in them would seize. the current thought is it's an original cap that is not opening, possibly causing the coolant to escape through the res overflow.

we ran a pressure test with a crappy tester and everything held save for a leak from the tester itself. with a little help for the tester it looks to be holding steady over an hour now.
plan is to order a new cap and expansion tank and see if it holds it. that and the rad are the only things not brand new.

[MrBurgundy]

Sounds about right. Cap seems like the move

[TobyB]

I kinda expect to add a bit more coolant after the system's been open.
It seems like air can hide just about anywheres in there, and only time
lets it fully burp out.

Which is also why I make sure the low coolant light works-
that thingus has saved me many an engine...

t