midnight mechanic

While driving during hot humid 90F day, I had to turn off the a/c to prevent the engine over heating. So does that mean the radiator is clogged? On the internet there's posts about using muriatic acid, vinegar, CLR calcium lime remover bathroom cleaner and prestone flush concentrate is a waste.

So what's a concise solution?

Ckforker

Was it in traffic or or running at speed? Could be the fan unless you have electric.

Also may be a failing thermostat, but less likely.

As far things to clear out the radiator, hopefully others will chime in. I've always had to replace the radiator as it had other issues.

GSLSEforme

As far as radiator being clogged ,have you had coolant level low enough to observe tubes thru radiator cap opening?Any crusty buildup on top of tubes? May be a dumb question,is ac condenser and radiator relatively clear from bugs. Ac not overcharged? When it is,condenser temps are higher and that temperature air is pulled thru radiator by fan making it slightly harder to unload engine heat. How fast does temp go back to what is normal in your car after switching off ac?
What condition is coolant,have you drained recently,what did what came out look like?OE cooling fan and clutch working correctly or electric fan,what size,cfm,shroud and how triggered? Do you have your bellypan installed and sealed to bottom of radiator? Do you have an oe type bypass thermostat?
Is this at low speed/stopped or while driving continuous over 30 mph. Is the engine getting hot enough that coolant is coming from overflow bottle out on to the ground,do you see a level change in bottle from cold to hot?
What percentage of gauge movement is there when it is overheating? For an average baseline,on a 1st gen cooling system at operating temperature,the temp gauge should be @1/4 travel from cold. On a day as you describe with ac on,@1/3 gauge travel.

Yes,lots of questions to arrive at a concise answer, being that we're not in front of your car it helps to know these things to give you the best answer.

Couple things you can check without disassembly,spending money or changing parts that could yield clues or answers:

The aforementioned eyes on condition of radiator tubes for crust corrosion,you can drain a little coolant when cold to expose top of tubes to see what they look like for @1/4" below top of tubes. While engine is cold,note level of coolant in overflow bottle. 1/2 way between min/max marks is a good spot-mark that level with a sharpie.Add enough coolant to just cover tubes in radiator and start car,watching radiator while engine warms,you will see when thermostat opens and you should see coolant moving rapidly across top tank of radiator.
If you see these things as described,it's a good visual check of thermostat operation,water pump moving coolant and radiator flowing coolant efficiently. Fill radiator to opening in neck and put cap on and drive car for @5 miles to pressurize cooling system and pull over and note level of coolant in bottle. You should see some upward movement of coolant in overflow bottle,@1/2" is normal,sometimes a bit more. Mark that level with your sharpie and look at level in the bottle next day before starting car. It should be real close to cold level mark you made.

If you have movement in your overflow bottle as described,it's a very good indication your system has no air/coolant leaks and radiator pressure cap is working as designed. The hotter ambient and engine temps the more important rad cap operation is. It needs to hold system pressure at its set point and allow coolant to flow to overflow bottle as it expands when it heats up and as engine cools off it lets coolant come back in to radiator as it cools/contracts keeping radiator full.

Another thing you can do is rent a non contact infra red thermometer and drive your car,duplicate your overheat conditions,pull over-leave running and aim thermometer at upper radiator hose @1" away from thermostat housing. What you see here is actual engine temp and will give you a good indication of accuracy of your temperature gauge in car. Keep in mind these in car temp gauges are an "indication" of temperature,not actual and gauge and sender being 30+ years old may not be as accurate as when new.
Aim thermometer at lower hose at radiator and note the reading,this will should/will be cooler by@ 20-25 degrees. This is an indication of how efficient your radiator is at shedding heat. If those #s are lower(not as much difference) it may be radiator is clogged a bit.Repeat this test after driving with ac off and rechecking. These numbers will show how much heat load ac is putting on radiator by subtracting ac on from ac off you can get actual #s.It is important to have exactly 50/50 % mixture of coolant/deionized water for cooling system to work at 100% capacity. Too much deviation from that affects heat shedding ability. Upper hose at thermostat,lower hose at radiator are only two places to check as they give real world #s accurately

I have tried all the brands of flushes and concoctions,some work to some extent and some show no improvement. When i have a radiator that i know has some issues,removing it and taking to radiator shop where it's cleaned and flow tested before and after costs about $40 with verifiable results. The cost of some of these cleaners is @1/3 cost of professional cleaning.Something else to keep in mind is,that $40 you paid to radiator shop is a little less than 1/2 what a new oe type radiator costs. Check Spectra brand. I use these in customer cars with good results without spending big$$ on an aluminum radiator.

A lot of specific info here. Following the process will enable you to figure out how to improve your cooling system before spending any money. If your car was brought to me with these complaints,this is how i would proceed before calling to tell you what the problem(s) are,what's needed to fix and how much it will cost. Hope this helps you define where trouble lies with your car. Any questions,or don't understand outcome of tests,post them here,will answer them for you.

midnight mechanic

Things will be ok if it is 85 F outside. The coolant looks healthy, and was changed 1 1/2 years ago so it is due for a change. The radiator was rodded out 15 years ago and the thermostat is 15 years old. Temperature gauge climbs rapidly to 1/2 with the a/c , with 90F ambient temperature , and will decline rapidly if I rev the engine with the a/c off, moving helps . But it will heat up slower the faster I go. Usually, I can cruise around with the gauge at 1/4, so I think the gauge is accurate. It's been my experience (1996) with a different radiator and different engine and same gauge, that when the gauge gets above 1/2, all hell is about to break loose in 5 minutes.

Also way backin 1996, I bought a radiator from Pep Boys, it solved the problem, but the radiator got all deformed and expanded. Got the current radiator from a radiator shop in 1998. It has worked well, and was rodded in 2004 out to satisfy the Atkins rebuilt engine warranty.

So the question is what should I do while I am changing the antifreeze?

GSLSEforme

Look in radiator with no coolant and look for white crust on top of tubes. Clean off all the bugs on condenser.Definitely change the thermostat if that old,i'm partial to Mazda,more accurate than oe,covered in another thread. Clutch fan,shroud,electric fan?
Not using tap water to mix coolant 50/50? The rate the gauge goes up and where it stays 1/2 it would seem to be inefficient heat shedding from radiator. Laid out some tests in prior post that'll help you figure out if radiator is culprit.Do the test with ac on/off and see how much it adds to engine temps.Maybe try those before you drain coolant.

t_g_farrell

iTrader: (1)

What kind of fan? Kind of sounds like a bad clutch fan to me as cforker mentioned.

midnight mechanic

it's a clutch fan. shroud is on. the fan is supposed to spin a 2000 rpm max?

midnight mechanic

changed the thermostat, and antifreeze after doing tons and tons of flushing. I used the Lowtox propylene glycol safe antifreeze. That **** is expensive! Engine temp seems happy now. Por little a/c cannot keep up with the heat load from record breaking temperatures.

There are a few bubbles in the a/c sight glass, so I don't think it is over charged. If it were the begininning of summer I would charge another can into the system. But cooler weather is coming.

I've never welcomed the end of summer before!!!