I’m having a problem with my coolant building up too much pressure. I start the car from cold and let it idle and in a couple minutes its shooting boiling coolant into the overflow. stock and megasquirt Temp guages arent reading hot either. Everything is brand new. today I tried running it a few times without the rad cap on to try and ‘burb’ the air bubble if that was the problem. I don’t think there was one because that didnt help at all. So I took out the radiator and coolant inlet elbow. I used the air compressor to blow air through the heater core lines, air came out the other end. I blew air through through the filler neck and through the water pump. and air came out the opposite ends. I ran water through the radiator. so I dont think there is any blocks. I also tried turning the motor over by hand to see if the fins on the water pump turned also and they did. After hooking everything back up. I had the same problem. It built up way to much pressure really fast. I also tried a compression test and that came out fine.
So what would be the next step I should try?
I was thinking leakdown test but not sure where I would go about getting a tester.
Leakdown test is the only way to know for sure if you’ve got a combustion leak into your cooling system.
[quote=“bracketracer,post:2,topic:31555"”]
Leakdown test is the only way to know for sure if you’ve got a combustion leak into your cooling system.
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agreed
does anyone have one I could borrow? or know of a place that rents them?
they are kind of expensive to buy for how much I’d be using it
You also need a compressor. However, the leakdown tester itself is reasonable. I’m quite sure I paid less than $125 for mine, and it’s a Matco
the thing that boggles me is that before the MS was installed it was fine going up and down the street a few times no boost. now that the MS is hooked up it has this issue…it leads me to beleive it is something electrical, but we already talked about all of this. the only place there could be left for a clog is in the heater core.
A clogged heater core should not build up pressure by any means. coolant does not flow through the heater core in series with the coolant system, it is parallel. If there was a clog, it would just no longer go there. I capped my heater lines off last year, and I never build up pressure. And I’m not sure what could be “electrically” making too much pressure in his coolant system. I’d do a leakdown, and not even waste more brain power diagnosing until that is done, since it is really the only way to check to see if the car is leaking compression.
–mark
^i was saying it makes one think it would be an electrical issue, but me and joe talked about this…knowing its impossible because all of the components of the cooling system are completely mechanical and in full working order.
Can’t imagine any sort of electrical issue that would cause monster pressure other than a cooling fan not working, but that would take more than a minute or two from cold.
What is megatune showing as coolant temp when the pressure builds up?
cracked head?..bad head gasket…cracked block. about the only things that will allow exhaust gasses to pressurize the cooling system.
sounds to me like a port in the head is shot and there is pres. going in there… so bad head or gasket
stock guage is at like 1/4 and before the temp in megatune gets to 190 its blowing boiling coolant into the overflow. If I cant get my hands on a leakdown tester by the afternoon then I’m just going to buy a new headgasket and replace it. The head and block should be fine. I had some machine work done to the bottom end and had the head surfaced and cleaned all by BRK, so if there was a problem I think they would have caught it.
anyone have a leakdown tester I could borrow?
I put in a new headgasket and swapped on the head from my original motor which looked to be in better shape anyways. and STILL the same problem.
I’m still trying to get my hands on a leakdown tester.
anyone have any other suggestions now that I changed those?
I did a cooling system pressure test and it came out fine. It didnt lose any pressure.
when you swapped heads how was the block? possible you have a crack inside a passage near a water jacket and it’s leaking in exhaust gases.
Did you measure the head or block surface for flatness? What were the numbers? Did you use a composite headgasket or multilayer metal one recommended for the recall on the 420a? Do you know how to bleed the coolant properly? I’ve seen these cars not bleed for a shit, I recommend going to carquest and getting this… LISLE 22150 or buy it on ebay… http://cgi.ebay.com/ebaymotors/LISLE-22150-AUTOMOTIVE-COOLING-SYSTEM-SPILL-FREE-FUNNEL_W0QQitemZ290135862157QQcmdZViewItem
^ Great link. That one is mine now. Definitely could use it for the FD, since the cooling setup wasn’t designed properly, with an opening at the highest point in the system.
Did you replace your thermostat? It’s a bit vague when you say you start the car up and in a few minutes coolant starts boiling over so I had to ask.
A stuck thermostat will make the coolant boil over and depending on your sensor location you may not show the car heating up at all while it can’t circulate.
Just another possibility…
If the car is stone cold and this is happening after say 1-2 minutes, rather than 5+ then ignore this, but when it’s this hot out coolant does warm up rather quickly.