Can anyone comment on this anomaly:
2000 Volvo V70 XC AWD,
1. Just installed replacement " 56" engine (72K miles confirmed by car fax) runs great but when idled up to temp coolant blew off thru reservoir cap. Hooked up coolant pressure test device, it retained zero pressure, until, I Put new cap on reservoir, then. it pumped up immediately to 20 psi, drifted down lower very slowly. I hear a hissing leak at reservoir so I've ordered replacement from Volvo. Very slow loss of that pressure

2. I left the coolant pressure gauge installed and ran the engine from cold up to normal temp, (3 pm on temp gauge,) at idle only, no driving on the street. Its not registered. There was zero buildup of pressure in the cooling system. Zero.

3. The cooling fan is not running so far at all. Thru its relays terminals I connected both individually to ground, the fan runs fine, each terminal grounded runs it at different speeds. Before a road test I need to nail down the cooling fan appropriate operation or run or risk overheat and engine damage.

Does this coolant pressure test denote a healthy normal engine? If so:

After that question I will pursue radiator cooling fan normal operation before "roading it" since I won't risk damage to "new" replacement engine

Freon seems low so AC running does not operate radiator fan.

Now that a competent coolant reservoir cap in on it it should develop more engine heat and operate the fan. I am new new to volvo thus stumbling around with these complicated creatures.

Thanks in advance
Rocket

 

do you have an OBD2 reader that can tell you the temp that the ECT is reporting? These cars do run positive pressure in the cooling system - I vaguely recall the pressure caps are designed to pop at 1.5bar ~22 PSI but not all models are same. 20 may be a bit high but if it comes back to say 18PSI or so on a fully warm engine, then it sounds like things are working as planned other than the fan. The fan should kick on when the coolant is in the 220F/105C range (which as you'd guess will put some pressure in the cooling system).

What I'd do is a quick resistance test of the ECT sensor (google for the values), consider you popped the pressure cap, I'd definately swap in a new thermostat and possibly replace the ECT sensor. Since you just did a replacement engine make sure you don't have any air trapped in the cooling. If you've idled the car for a few minutes and the level in the overflow hasn't dropped you are probably good. With that out of the way, next is to see if you can get a reader than can measure the engine's temp sensor output. That will tell you if your car is turning on the fan at the right temp.