Mon, 27 Jul 1998
Hey Glenn,
I am still getting to know my 1973 1800ES (bought in March). I recently took it to a mechanic because it had overheated a couple of times. He found that the thermostat was stuck, and replaced that, but it was still overheating, so he boiled out and flow-tested the radiator, and then he sent the cylinder head out to be milled and pressure tested and replaced the head gasket. (He also, somewhere in there, replaced the temperature sending unit, or so it says on my bill.) I picked up the car and drove it around a little while (AC on, stop-n-go city traffic) and sure enough, it overheated again. I got the car back to the shop and the guy was mystified.
I know from reading your site that these cars tend to overheat, but if I'm going to drive this car I have to reduce that probability! So here are my questions:
1. The mechanic wants to put a much lower thermostat in (the one I have is 195). He was able to put his hands on a 180, but since he felt I really needed a lower one (160), he wanted to check around and see if he could find one of those. So he sent me off with no thermostat for the time being. I haven't driven it much in the couple of days since, but even in the traffic on the way home, I could see that the gauge was veering close to the red. Do you think having no thermostat is better than having a 180? (It makes me nervous, but if it makes the car less likely to overheat...) Do you know if there are thermostats lower than 180 that will work in an ES, and if so, do you think it's a good idea?
2. I read your piece on electric fan installation. Maybe I should try that. How is yours holding up? (The mechanic mentioned to me that I might want to do this.)
Beth Pearson
Beth -
We've had a streak of hot weather here in Fort Worth, and I'm having difficulty keeping the P1800's engine cool. The electric fan helps when the temperature is below about 98 degrees, but lately it's been over 100 every day.
I'm going to implement Plan B very soon (or is it C or D?), which is to have a better core put in the radiator. The local radiator shop seems to have a variety of new cores with various efficiency ratings that they'll install for $200 or so. I have a spare radiator I bought from Don Thibault, so I'll have that one recored and then switch it with the one in the car.
I think your mechanic was right to check the thermostat and remove it as a last resort. It won't harm the car to run without the thermostat while the weather is hot. However, since the car still overheats, replacing the thermostat, even with the available 160-degree unit, will not solve the problem. And when the weather turned cool, you would notice poor performance and gas mileage because of the engine running too cool.
There are three temperatures commonly available for the Volvo thermostat: 160, 180, and 195. The 180-degree thermostat is the best for year-round use. The 195 should be used only in frigid weather, and I've always found the 160 to be fairly useless.
In all the years I've owned the P1800, it has always had trouble in hot weather. It has been out of control only since I rebuilt the engine last year and increased the size and compression. I already have tried every remedy except the radiator, so that's what I'll tackle next.
The only other thing I can think of to make the cooling system more efficient is to use a smaller pulley on the water pump, therefore making it pump faster. I have seen these marketed for American engines, but so far have not seen one for Volvos. If you know a good machinist, pitch it as a challenging project (and tell him to make two!)
-Glenn.