1998 V70 No Heat, engine overheating

[erikv11]

If the thermostat is stuck closed, then the coolant can not circulate to the radiator and the engine will overheat. Absolutely. The episode you described the thermostat may have at first been stuck closed, then it finally opened properly and the car ran at normal operating temps.

Are you sure the coolant:water mix is 50:50?

[mikealder]

What level of concentration is the engine coolant, if it contains mainly water it could have frozen in the pipes preventing coolant flow.
I doubt it has anything to do with the thermostat as you still get heat from the heater with the stat shut as the water pump circulates coolant through the heater core all the time the engine is running.

Only three ways to cause overheat and no heat from the radiator:

a/ Coolant frozen preventing the fluid from circulating.
b/ Impeller fallen off the water pump preventing the coolant from circulating.
c/ No coolant in the engine.

Mike

[erikv11]

If the thermostat is stuck closed, then the coolant can not circulate to the radiator and the engine will overheat. Absolutely. The episode you described the thermostat may have at first been stuck closed, then it finally opened properly and the car ran at normal operating temps.

Mike is totally correct, given what you said about the heater this part of my post is wrong.

.... Are you sure the coolant:water mix is 50:50?

At least I wasn't stupid with this part ...

[volvooh]

Its a 50/50 mix...I replaced the heater core last summer and refilled with a Volvo 50/50 mix.

[volvooh]

Well....I just went and started it and opened the reservoir...Not completely frozen, but very slushy...hopefully I don't have a cracked block.

How could it be a 50/50 mix and still freeze-up like that?????

[mikealder]

Not completely frozen, but very slushy...

Looks like you have found your smoking gun! - get it drained down then add new Volvo coolant to the correct mixture, coolant can degrade over time and if you have been topping it up at all with just water that further weakens the mixture - I doubt it will have done too much damage as long as you shut the engine off and haven't been driving it much in the really cold weather you guys seem to be having at the moment - Mike

[volvooh]

I called my indie around the corner. He is going to let it sit in his garage tonight and do a drain and fill tomorrow.

[cn90]

In the US, you can use Green Prestone coolant.

[c70_lindsay]

I would double check the mix. I missed in your original post about how cold it was outside. You can buy anti-freeze testers that will show you at what temperature your antifreeze is good till. Even if it is not freezing completely it can "gel" causing your thermostat to remain closed, until the engine gets hot enough to open everything up. Your problem could easily be solved just by putting in a lil' extra ant-freeze.

[erikv11]

We are all saying the same thing: the coolant is not 50/50 and it is freezing.

One way this often happens is, when the system is flushed out with water, you never drain all of the residual fluid. So you can't drain and then fill up with 50/50 or it will be too high on water. My preferred way to refill is like this:

(1) Use only distilled water.
(2) Flush the system well with water to remove all of the old coolant, so only water is in there.
(3) Drain again, as much as you can.
(4) Total cooling system capacity is 7.4 quarts. So add about 3.7 quarts of pure, undiluted coolant (I use Zerex G-05, it is very similar to the Volvo coolant).
(5) Fill up the rest of the way to full with water.
(6) Run the car, likely it will "burp" some air and be a little bit low. Top off with water, watch it for a couple days and again only top off with water. The system is now full with a clean 50/50 mix.

With the little bit of leftover coolant in the jug, add an equal amount of water. You now have some spare 50/50 to use later if/as needed.