Okay, a little background first

The engine in this car has had this problem since it was brand new. The car is actually a 1990 240DL automatic sedan, but the drivetrain is out of our old 1989 240DL auto B230F which gave its life in an accident to save my Wife's life and that of our Boxer. The front end is three feet shorter than it was before, but the engine was still running and all four doors still opened and closed.

In any case, the engine has been completely rebuilt (sucked in dirt during accident) and all cooling system components have been replaced with NEW parts. This includes:

Thermostat
Heater Core
Heater Valve
Radiator
Overflow tank and cap
All hoses
water pump
fan clutch
fan blades
aux fan (added)... yes, pushing air the right way
Block and head have been flushed and cleaned to perfection, yes, even the water pipe running along the passenger side of the engine!

Now, for the details of the problem. If the weather is below 85F, there is NO PROBLEM AT ALL. Up around 90F, with the AC running (yes, condenser is new too) it begins to overheat after about 3 minutes of idling. The temp gauge, over this 3 minute period, goes from dead center right to the white line below the orange overheat area.

Once the overheat condition occurs, I can rev the engine, lets say to 2500RPM and get a slight reduction in temperature. If, however, I crack open the heater valve for as little as two seconds and then close it again, the engine cools right back down for another two to three minutes... cycle then repeats!

Keep in mind, this engine has had this problem from day one when it was new off the showroom floor.

In my humble and semi-educated opinion, it seems like the coolant is boiling in the head and that "cracking" the heater valve open provides a flow path for the gas to escape which results in the measured temperature dropping.

Out of these observations the first thoughts that come to my mind (or whats left of it after restoring this car), is that there is insufficient flow from the waterpump to "overcome" a "vapor-lock" type situation in the cooling passages of the head. This leads to thoughts like:

Is there a higher pressure (narrower clearance) water pump available?
Is the idle simply too low at 750RPM.
Should I try to "rig" a different sized water pump pulley?

Thoughts, comments, and or curses will be appreciated!

Thanks,
John

One small mod which may help is to jumper across the pressure switch which tutrns on the pusher fan in front of the rad. (Frequent contributor Chris Herbst has mentioned this in several posts.) Find the switch on the passenger side frame rail just aft of the radiator. Remove the connector, and make a jumper from decent-gauge copper wire. Tape it up and stow the now-loose end. Tape up the end of the pressure switch as well to keep it clean in case you want to restore things to original condition someday. Your pusher fan will now run whenever the AC is switched on, which may not cure your condition but ought to help a bit.

Also I second the opinion in other posts about replacing the thermostat. It's too cheap a component to have a great deal of reliability built into it.

This May not solve your problem; but may solve some else’s.



Being a person who has only put on a water pump on my 85 240 one time in my life I don't know much about cars but I am learning. I had a similar problem. At 85 degrees no problem, as soon as the outside temperature zoomed to the ninety with the AC on in stop and go…..trouble would come to the old Volvo The temperature gauge would move up two needle widths in three minutes. I would spend my time in traffic watching the temperature gauge more than the car in front of me. I did all the things you did to your car. Same problem. I put on an electric fan I found at a bone yard for $20.00. Same problem. I took the electric fan off; put the mechanical fan back on the car. The second problem in ninety degrees temperature was at speeds above 75 mph; the car would over heat by the two needle widths while moving at high speeds. By the way I live in the Washington D.C. area; the posted speed limit on the Capital Beltway is 55, the cars top 80 mph easily. I took it to a Volvo dealer; they could not find the problem.

My wife and I were on a road trip. She said the car sounds like wind was gushing in the front of the car or right under the engine. I look at her wondering if she really heard what I had been hearing for past six months on each road trip. I asked her how long she had been hearing this sound……she said about six months. Next question was why didn’t she tell me. I didn’t ask.

I came home one day and thought about what we were hearing. I went down to the garage, got under the car; and started looking for anything that may be loose near the front of the car. I found these three holes under the bumper. I don’t know what you call this thing but it is under the front bumper. It looks like it could be an air dam, which directs air to the condenser and radiator. The front of this thing had fallen down so no air I suppose was going to the radiator. I got one from a bone yard and installed it. The problem disappeared. Now at ninety degrees you may find me setting sitting on the Wilson Bridge in a 20-30 minute traffic jam, AC blowing…for a 240 it is not bad, and looking at the car in front of me trying to get to that fine state of Virginia. .

Junior:

Thank you very much for the idea! As it turns out, I had already replaced all the plastic "ducting" in front of the radiator when I rebuilt the car, but I checked again anyway. Unfortunately, everything was fine. On the "bright side" of things, however, I did find the correction to the possible "design flaw"!

Since I have now seen this "issue" in three B230F powered 240s, I had to believe that it was a "fundamental" design problem. As I stated in my initial post, opening and closing the heater control for a few seconds let the engine cool back down into the "normal... dead center of the gauge" zone. Based on this, I made the assumption that the coolant was boiling in the head (at the temp sensor) which was causing the gauge to read a very high temperature.

I finally spent the "big bucks" and installed CLEAR high temperature hoses to the heater core. Once the "overheat" condition appeared, I cracked the heater open and watched the fluid flow through the hoses... end result... a TON of air bubbles BEFORE fluid returned! CONCLUSION: Either A: fluid was boiling, or B: water pump was cavitating and the resultant "air" was being trapped in the head (Physics doesn't support this one very well at low RPMs).

As it turns out, when the heater is turned off, the valve BLOCKS flow out of the head and back into the pump, quite unlike "American" heater valves which don't block, but rather redirect flow around / past the heater core. As a result, I installed a semi-kludge-custom bypass valve at the firewall for the heater core and then tested the impact.

I drove the car in 94 degree weather for 20 minutes, pulled back into the driveway and let the bumper TOUCH the garage door, and then let it sit there for 30 minutes idling. The end result was that it NEVER overheated as indicated by the temp gauge or the thermistors in the upper and lower radiator hoses!!!

Once I get "done" refining the (currently crude) bypass valve for the heater core and its controls, I will make the details available on the brickboard.

Once again, Thanks for your input, and I hope that you and others find the above information useful! After all, a Volvo saved the life of my wife and our Boxer dog... its the least I can do! If anyone is interested in what was "left" of the car after the accident, let me know and I'll provide JPGs!

Later,
John

Well I just had a bad experience with the thermostat. Brand new Volvo unit (Walher) 92C, did not cure overheating. Replaced a bunch of old stuff with new as you do to solve a problem and checked everything out.

Came back to that darn thermostat and replace again with new Volvo unit, this time 87C. Temp is real nice now at 1/2 and super stable. The previous thermostat was just shot (as well as the org unit I replaced).

Lesson here is: Don't trust the thermostat! They are cheap to buy ($12), easy to fit and do wear out (wax can leak out). Typical fail mode is hot. Try an 87C first before searching furhter is my advice.

Reg,

Jorn

The heater core having an effect indicates that the cooling system is not removing heat quickly enough. But, with all the new stuff you put in, the problem is not so obvious.

Is the coolant a 50-50 antifreeze and distilled water mix?

Have you "burped" the cooling system to remove air bubbles?

Are you running the 87C thermostat?

Sounds like a fan clutch problem, is it possible that the new one is a dud?

That all I can think of just now.

Good Luck,

Bob

:>)