Just bought a very nice 1990 745GL. Yesterday I drove it home from Ft. Lauderdale to Gainesville/Ocala area, about 325 miles.

Drove it home, about 325 miles, much of that at over 90 mph, all of it over 75 mph. Confirmed today that the upper hose stays as soft as when cold, even when well heated up and run for quite a while. There is no pressure in the coolant tank.

There is NO coolant consumption, no evidence of coolant on the spark plugs (they are, in fact, the closest to textbook perfect, light/medium brown, plugs I have ever pulled from a car), there is NO coolant in the oil, NO oil in the coolant, etc. NO smell of coolant when running the heater (it was cold here in Fla, so I did run it for quite a while on the way home yesterday), NO leakage from the heater control valve, NO seepage from the water pump weep hole (or anywhere else). There is NO white exhaust, NO white residue in the exhaust pipe, etc. The car runs perfectly.

I know: Do a compression test, and pressure test the cooling system. Will do, but in the meanwhile, what could it possibly be?

Addendum: Why do cars hate me? While pulling the plugs on this car, I accidentally broke the #1 plug wire. Then I get a phone call from my wife up in Gainesville - the Turbo stalled and started running rough, don't know if they can make it home. Why? Why both cars at once? Well, I fixed the #1 wire, and then called wife - she filled the tank and then, lo and behold, the Turbo is running perfectly, they were almost home when I called her. I really do think cars hate me.

But, the main point of this post is about not holding pressure in the GL's cooling system. And, how could it run so hard for so long if there was a serious problem in the cooling system?

Turned out to be a shot pressure cap on the coolant tank. I put a known good 75kPa cap on, and, lo and behold, pressure and stiffness in the upper rad. hose.

And I have almost the complete opposite situation. I have new radiator, hoses, heater valve and water pump ok. When the car is running everything is normal temp with no leaks or problems. After it sits overnight coolant has seeped out somewhere. I can't find where it came from, but 4oz or so is on the ground. When I take the new coolant cap off to check reservoir, the system is still holding major pressure 24 hours later. Guess cars have all sorts of evil ways to hate us...

If the new cap is not a genuine Volvo cap, but rather one of the aftermarket ones sold by FCP and IPD, it is likely not venting correctly. I ran around with an intermittently defective one for several months before I noticed.

Black (75 KPa) Volvo-branded cap is generally regarded as the safest choice. you can get them cheap off practically any 240 in the junkyards, or buy a new one from the Volvo dealer for about $15.

John

Thermostat stuck open or been removed?

The temp comes up at the same rate as my Turbo, is at the normal, i.e. vertical needle, position in about 2 miles. Never goes over or under.

Bad pressure cap?
Your car is running close to pig rich; FI cars have next to stark white plugs when running properly.
Nice light brown =~12.5:1, 3- way cat converters work at 14.5:1.

This could be it. I put a known good 75 kPa cap on at home, while the car was hot. As it cooled, the 75 kPa cap at least held a partial vacuum, as shown by a hiss when opening it.

As for rich mixture, probably right too: gas mileage was at the low end of expected range on trip home.

Is it possible that PO put in Evans no pressure coolant?
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