Remember that the water pump only suggests the coolant to flow. It is not a positive displacement pump. If it cannot suck it cannot push coolant, the temp sensor may turn the fan on and off but the coolant may not really be circulating properly. I have seen fractured plastic impellers and corroded away steel ones also. A restricted radiator may get hot to the touch but not be flowing properly.
Or the new cap might fix it.
I like to fill the cooling system with water and start the engine without the thermostat housing installed. I then rev up the engine and see if the pump blows the water out of the engine.
just more stuff for you to ponder

 

It was my impression that without the water pump pulling coolant and then pushing it along, there would be no flow in the system other than that caused by local pressure differences and temperature differences.

Yes, if the impeller is trashed but still attached it is quite unpredictable as to what will happen. However, based on previous discussions and your last post, the court should shoot out of the system if there is no thermostat in place as the thermostat provides a restriction at all times, a restriction that varies in order to maintain optimal operating temperature.

For the record, you supposedly cannot fit a stant thermostat in the stock thermostat housing . Not sure how or why that is . I also can't seem to find a stant housing for the matching thermostat....

The radiator does not have too many miles on it and has also not just sat and had junk precipitating out of it while sitting in place like the white car. luckily I did a drain and fill on that one before I gave the car away.

It also seems that the line coming off of the top of the expansion tank cannot possibly be routed to the ground because then the system would not be sealed. I traced it today and it led to what appears to be the intake manifold just past the throttle plate.

So what is the deal?

Is it that the system is sealed and holding positive pressure but there is a small vacuum being pulled from the intake manifold or per physics there is a 15 psi pressure in that line where it enters the intake manifold. However that pressure cannot overcome the head pressure of the coolant in the expansion tank, so that is why no fluid gets pushed out of the expansion tank under normal conditions when the coolant is at the right level. Plus it serves as a path for trapped air to get out of the system.

So before I drain the system I am going to pressure test it. I purchased a compressor fed regulated pressure tester that allows you to dial down the maximum pressure at the unit. Hours of ridiculous research have determined that you can either buy a mighty vac MVA 107 with the male connector integral to the test cap for $35 or mighty vac will sell it to you as part of a super mega deluxe kit that costs like $200 bucks. It is not in any other mighty vac kit. Review say it is the most commonly used testing cap and fits Saturns. The other option is to buy a stamp adapter to match the threads of the expansion tank and then attach a stamped tester to the other end. Again this is all for testing attached to the expansion tank.

I do appreciate the wisdom of putting a t in in order to also test the cap. However the only place that seems simple is that line coming off of the top of the expansion tank. Physics tells me it should be at the same pressure as the rest of the system. I'm not sure why I can't seem to convince myself of that period but that is why I bought the money back style compressor driven device with an integral line and fitting on the end. I will just have to find the appropriate T fitting it attaches to.

I am also aware of that it is not exceedingly difficult to make your own cap for pressure testing. People do everything from drilling out rubber corks that close up the opening and then putting regulated compressed air to the hole with the gauge attached via a t. I found one of the MVA 107s at a not total ripoff price so I bought it but they are extremely hard to find as a standalone items.

My parts orders for the new cap, this testing cap, the compressor driven tester, etc are all over the place in terms of arrival so I will report back once I get back to work on it.

Thank you for making me figure this out myself for the most part. If you (colloquial) can't explain it then you don't know it. So by the end of this I will be able to explain all of it and address the issue which is the goal.

 

The hose from the intake to the expansion tank is to promote flow through the manifold and to purge air back to the tank. This is the hose to remove and add a T and another short piece of hose to. This way you can check system integrity all at one time. If you have a gauge on the pump you can verify cap release pressure. I have never heard of a one time cap, they should just vent at 15 lbs or so and hold below that.

 

Thanks Andy.

I think my one-time cap comment was actually a reference back to the olden days when radiators had vented caps and the advice on the street was that if your vehicle overheated, you should replace the radiator cap. Sorry about that

My other question was rather these valves are single release valves as in they opened once and that's it or if they close back up on the pressure goes down. Some of the Caps I have used recently feel as though the very center is raised above the flat surface of the top of the cap which makes me wonder whether or not the pressure release mechanism is fully receded. But we shall find out as I will test the lot of them.

Truly appreciate the guidance.

Damn I wish I had a lift of any type besides the one attached to the end of my Jack.