We put a new radiator into my sons 92 240 last night, and also replaced the thermostat. Today it was heating up to the red zone on the dash gauge. We did not flush the system as time did not allow last night. And there was a layer of crud that settled out in the container of the old antifreeze. The temp did drop back to normal after a few minutes of idling in the driveway, but he said it was running hot while on the highway, and I saw it was hot when he pulled in, but again, it did drop back down to normal. I guess I figure some crud could be preventing the thermostat from opening? I never had an issue before with the b230's after a radiator change, anyone have any ideas what could be the issue?

It is not an oem Volvo thermostat, but I have not had problems with the generic thermostats before. I know there is an outside chance the thermostat is brand new and bad, but I am thinking through what else could be the issue before throwing more new parts at it.

Have a similar problem on my 1989 245 DL but haven't had radiator or thermostat replaced, instead had hose to heater burst and commensurate with that high temp reading. Took IR temperature unit and focused it on engine block where temp sender is, found it read 175 degrees. Then installed VDO temperatures gauge in 52 mm hole in dashboard for auxiliary gauges and taped into yellow wire on instrument cluster believe it's position 31/2 in wiring diagram. Auxiliary temp gauge read hot about 210 degrees but not 240 degrees which is top temp grade. I think I have a fault sending unit. You have to do similar trouble shooting. If block gives high temp reading commensurate with instrument cluster then you have to troubleshoot the cooling system further. Meaning if there is no air trapped in the system look for a bad water pump as a lack of circulation causes over heating.

Thermostats can be bad, new out of the box.

Have you measured the temperature of the upper hose, thermostat housing, etc ? If not, it is a great excuse to buy on IR temp sensor/reader.

Greg

As Art indicated, you likely have either a temp comp board giving you false readings or you still have unpurged air. If that annoying are bubble is right under thermostat...argh.

If neither of those prove to be the case, what triggered the Rad swap in the first place? Preventative maint, leak or where you already having a high temperature reading? If the latter, we might need to do some troubleshooting on cap, belt, waterpump, blockages in front of the condenser coil, etc.

Of course, it is still probably that big fat liar the temperature compensating board.

Wow, I was not aware of the temp fake issue! And I have had quite a few 240's, but they somehow always had working temp gauges. I was concerned about an air bubble, and I guess there is no really good way to bleed the thermostat housing/water neck, other than using a good make of thermostat? The reason we changed the radiator is it was a plastic tank Volvo oem model, and the tank split along a fin. It was showing hot prior to the radiator/thermo change, and we figured the coolant level was the issue, and that while it had a very low coolant level and the car heated up quite high it cooked the thermostat in it, so we of course put a new one in along with the radiator. I actually just bought him a complete 1983 turbo dash/gauge set, so he could have a tach to replace the clock. I always liked to add a tach to my 240's but it has been a long time since I have done a tach swap. I cant remember, but I seem to think the 1983 dash is different than the 1992, correct? I know the tach will fit if swapped, but what I am getting at is can we just swap out the whole dash and then have an immediate temp circuit board elimination because its an 83, and from what I read on the fix, the pre 86 did not have the idiot temp circuit?

No, just take the tach from the 83 and bypass the compensation board on the '92 cluster. Nothing else is even remotely compatible, as you will see when you get it apart.
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Art Benstein near Baltimore

What Art said. I will admit to having bought the IPD bypass kit for the very clear instructions on bypassing the second worst decision in Volvo Red Block history (the choice, and continued use of the Electrolux designed blower motor). They are well worth the $14 or so dollars but the reality is that you only need a bread bag twist tie wire...

99% of the time you can purge the air even under the thermostat by turning the heater on full blast and warming up the car at idle while squeezing the upper radiator hose about every 2-3 minutes after you are up to temp. It might take 20-30 minutes after you hit operating temp if the thermostat does lack the weep hole.

Update: When my son got home with the 240 right after a 30 minute run, he laughed and said " I did what you told to do and smacked the dash, and it went to normal!". So I guess we know its the 'idiot' circuit board in the dash. He will remove it and solder in a wire to replace that temp circuit riser card when he does the tach swap. Thanks for your help guys.

It kind of reminds me of the old TV sets when we had to smack the side hard enough to get the picture to come in!

Hi there,

You don't mention having deleted the infamous compensation board, so if you have not, give a swift rap to the top of the dash above the instrument cluster when the gauge is high to see if that affects it. If so, see Notes on the Temp Faker - Or That Temp Comp Board

As generic tstats go, the important part is the poppet (air release device) at the physical top of the unit. This feature of the OE and certain aftermarket thermostats really helps get the air out after a flush/change.
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Art Benstein near Baltimore

"While their life may be 20,000 hours, a wayward baseball will break one of these $10 to $20 bulbs as easily as a 25 cent incandescent. "