Running Hot

[ol' yeller]

Here in the Great Northwet we are experiencing a heat wave.  We have had a couple of weeks of temps in the mid 90's.  Thankfully yesterday and today it has dropped into the 70's.  I had a long drive, 40 miles in the heat, all on the freeway a few days ago when the outside temps were in the low 90's.  I had the classic convertible owner's debate, top up or down.  I decided to put the top up and ride in air conditioned comfort.  After about 20 minutes of stop and go freeway traffic, I noticed that the temp gauge was creeping up slowly.  When it got to within 2 bars of the Hot reading I shut the AC off and watched the temp go back to the more normal range of mid gauge.  If I turned the AC back on, it would begin to creep back up.  I left the AC off for the return trip and it stayed at the normal middle reading.  

 

Here's a little background on the car.  When I first got it 3 years ago it had been sitting a lot and it appeared that the coolant hadn't been changed in a long time.  It was a nasty rusty orange color.  I took it to my mechanic who drained and flushed the system and discovered I had a couple of leaky soft plugs which he replaced.  Fortunately they were the easy ones to replace.  Fast forward a year later and I again had him drain and flush the coolant to make sure there wasn't any problem.  The temp gauge always goes to the reading at the top of the arc and stays there until recently.  The coolant level has remained fine since my mechanic replaced the soft plugs.  The car now has 103K miles on it. 

 

I know that there are 2 fan motors and sometimes one will quit which will affect cooling especially when the AC is on but both of my fans are spinning.  Does one or both spin faster when needed and how can I test that?  I suspect that I have a clogged radiator from the original problem of dirty coolant.  I guess I will take it to my mechanic and have him flow test the system and replace the radiator. Hopefully it would stop there but I guess it could also use a water pump (it is not leaking) and maybe even a heater core.  Am I overlooking something? I never tried the old hot rodder's trick of running the heater to see if it would cool it down some.  Thanks in advance.

[Guest Rp1967]

Another problem area on older cars with a/c is cooling fins on the front of the radiator.

The air flow is enough to push dirt through the condenser but it gets caught in the front of the radiator.

The only good way to clean this area is remove the radiator and repeatedly spray it with water then compressed air until all of the dirt is forced out

Poor air flow is just as bad as poor coolant flow

[Guest Corvanti]

hi. first off not having a 90/91, i don't know what the "bars" actual temperatures are. someone hopefully will add that info. i've read here and on ROJ that 230* is not bad on the engine.

 

the heater core shouldn't be a problem. AFAIK, as on other vehicles, no coolant flows thru it when off. that's why turning the heater and the fan on full helps get "cooler" coolant into the flow and drops the temp.

 

quite possibly, the radiator needs to be re-cored or a new one installed. the "orange" was rust (unless someone put the wrong antifreeze in it - the orange stuff).

 

i'd wait until i knew what the true temp is where the "bars" indicated. a flush & fill may be in order as well (as above) a good cleaning of the radiator fins before other more costly repairs.

 

hope this helps! 

[ol' yeller]

The outside of the radiator looks clean as 2 years ago I had the AC converted to R134A and replaced the condenser. The AC tech had removed the radiator and cleaned it at that point.  I'm thinking I may have something internal going on.  Thanks for your suggestion though.

 

Greg 

[ol' yeller]

Thanks Kerry.  It was bad rust in the tank.  I am leaning towards a radiator replacement and getting a good flush too.  I can do the radiator replacement but i don't have the facilities to do a good flush. As for the bars, Normal was always at the top of the arc for the bars or about half.  Now when the AC is on it goes to within one bar of the HOT reading which I am sure is too hot.  I didn't want to overheat so I then turned off the AC and it cooled down to where normal was. 

[Barney Eaton]

Before you start replacing parts,  verify that both of your cooling fans are coming on.

Under normal conditions with the A/c on,  both are running but relays put them is series (so they are running half speed, like they are only seeing 6V)

When the block sending units show coolant temp around 220,  the ECM switches the fans to full speed  (this usually happens in town...stop and go traffic)

[ol' yeller]

Thanks Barney.  I wondered if they were running at full speed.  This morning I started the car cold and only the rear fan was running. I switched on the AC and the front fan began running along with the rear fan.  I didn't let it run too long.  I guess I could let it run watching the gauge and see if they speed up when it shows hot.  If they don't speed up, what should I look at, fans or something electrical like a thermo switch?  I'll spend some quality time tomorrow with my FSM.