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Discussion Starter · #1 ·
I feel like this is going to be an obvious answer and I'm going to feel dumb for asking but my 81 rabbit pickup 1.6 coolant system has random spontaneous problems, so starting with the reservoir I can't tighten the cap on all the way otherwise it builds up steam in the coolant system and overheats, so I leave the cap slightly loose, the system doesn't build up any pressure when warm I can take the cap off knowing that nothing will overflow. It gets up to operating temp and holds good, but heat is never warm, very rarely after I've been driving it for a while the engine will get slightly warm, about the middle notch on the temp gauge, and coolant will start to flow out the reservoir for a little bit, but let the engine cool and top it off and it won't do it for another couple weeks. My guess is there must be something getting plugged somewhere, I bought a new radiator, fan switch and thermostat to hopefully fix it, anyone have any ideas?
 

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Question for you. Does the reservoir have a constant flow of coolant at idle from the radiator?
X2

Tanks and caps fail to seal correctly I have had to replace 2 10 year olds ones recently as well as a new all aluminum Radiator.
Do the glove trick to rule out a bad head gasket.
 

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Question for you. Does the reservoir have a constant flow of coolant at idle from the radiator?

Kind of what I was thinking, like his water pump just isn't doing the job and the only heat exchange that is going on is by what is boiling in the cylinders and getting back up in the reservoir.

That hose coming in from the radiator should be peeing like a race horse after a long ride! And get stronger if your engine is revved up a bit.

When you open up the bottom of the thermostat cover see if you can look up there and spin the water pump freely with a screwdriver or something like it. The belt should be in place and prevent that impeller from spinning.
 

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Lack of flow at the reservoir can be an indicator that the radiator is plugged.
This is why you need to flush and back flush your cooling system every 2-3 years, and install new tested t-stats (with or without the 1/8 hole drilled in the lip), as well as doing your heater core separately. The Jugs as well as caps are under pressure and subject to hot fluids over time plastic parts can distort and cause fit ment issues. I have also seen New Jugs that don't take well to ne caps it is as if there is no quality control on products any more. "Chinese" made parts are an iffy lot, I have gotten quite a few things that have leaked from the get-go.

You can also use a pressure cap on your expansion tank and pump it to 1bar, or 14 psi and see if any leak occur.

Plastic Impeller Water Pumps have been known to break loose of the drive shaft and spin freely or not spin at all. They also tend to wear down and not pump the volume of water one would or should expect. Specifically if you don't see any return flow into the expansion tank at the cap, it would bubble out during start and stream once the t-stat opens.
 

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Discussion Starter · #8 ·
Ya it's nothing crazy, it's usually a constant trickle coming from the hose, so I'm assuming the radiator has some junk in it
 

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Read my how-do-I-flush and back flush my system.... it's in the FAQ's
 
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