Hello all! This is a continuation of my seized thermostat bolt saga (thread). The thermostat has still not been replaced, and I'm going to have to take it on a trip for 3 weeks. In cold weather it wasn't a problem b/c I blocked the front of the radiator so that the engine could stay toasty warm on the highway but, now that the weather is turning warmer, I'm wondering whether the temperature gauge will warn me when the coolant temperature gets dangerously high. I saw or heard somewhere that the needle rises to about 3 pm (9 pm?) when the engine comes up to temperature, but it won't rise above that. Can anyone clarify whether I can depend on the gauge (and remove the cardboard blocking the radiator in time)?

 

DG, it's not clear why you are worried about overheating. If you have to block the radiator to get or keep the engine up to operating temperature, the thermostat appears to be stuck open. If that's true, you should not have to worry. Running with an open thermostat is not optimal, but that should not cause significant damage the engine. I imagine your gas mileage will suffer and you could accelerate the formation of deposits. I would change the oil more often in this case, if the engine does not reach normal operating temperature.

If you are worried that it will suddenly become blocked closed, then the temperature will go up quickly. I don't know how much time you will have, but it won't be long. You won't have five minutes to figure out where to pull over. My gauge normally sits at about 3 PM or just a bit higher.

Have you thought about renting a car for your three-week trip?

 

Thanks for your reply. Yes, the thermostat is stuck open. What I'm not clear on is when I should remove the cardboard that is blocking the radiator on a warmer day. If the temperature gauge is reliable, then I can just see it rising to a dangerous level well above 3 o'clock. But I heard or read somewhere that the needle never rises above 3 o'clock which presumably means it won't warn me when the coolant is getting too hot.

 

If the thermostat is stuck open, I see no reason why the temperature gauge will ever rise significantly if you remove the cardboard. With the cardboard, the fan should still function normally, kicking on when the temperature goes up. AFAIK, my cooling system has worked well from day one (bought new in 1994). I occasionally have seen the needle move slightly above 3 o'clock, but not much, and I have no experience with overheating. It is hard to imagine Volvo designing a temperature gauge that only went halfway up.

If the weather is going to be warm, if you're worried, I would remove the cardboard for that day's drive. Remember, it's a lot better to run a bit cool than to overheat. But, even with the cardboard in, I wonder if you would ever overheat at highway speeds. You will still have a lot of airflow, and the fan should kick on. Does your fan still kick on or is the engine constantly too cold for that to happen? I think your biggest problem may be driving long distances below normal operating temperatures.

Why not do a test around your town, leaving the cardboard in on a warm day. I believe you've already had some warm weather in DC.

 

Plot twist: Today I was able to finally free up the seized bolt on the thermostat after trying all kinds of things on it. Now, it seems like coolant is leaking, even though I re-tightened the bolt. (Maybe using an impact driver on the bolt cracked the thermostat housing...) I'm going to call the mechanic first thing tomorrow.

In the meantime: Yes, the fan kicks on when the engine is hot. I agree that it would be weird for the temperature gauge not to show when the engine is getting too hot, but I thought I saw or heard somewhere (maybe a YouTube video about the thermostat?) that the needle doesn't go much above 3 o'clock. That's why I started this thread--to get a confirmation or rebuttal. Driving it around town in the warm weather to see what the temperature gauge will do, that's a good idea, thanks. Hopefully, I can take the car to the mechanic tomorrow or Friday. Friday is supposed to be hot. But, also hopefully, the mechanic can replace the thermostat right away and I won't have to deal with the gauge anymore. I'll post an update.

Thanks for your thoughtful reply. I appreciate it!

 

Best of luck, and thanks for keeping us updated! Yeah, impact drivers can do that...best to use them only for loosening. Torque wrenches are your friend. I haven't had occasion to look at the thermostat housing on my 850, but I hope it's not complex and is easily replaced (i.e., that you can get one in your hands quickly). I see that FCP lists one.

 

Problem solved! Turns out the impact driver did not crack the housing. The mechanic swapped in a new thermostat, no problem. See my original thread for details.