I have owned my 85 for almost 22 years now, and the cooling system on it has never worked well in the summer.

First, I replaced the temperature sending unit that turns on the cooling fan with a 185 degree unit. Next I replaced the thermostat with a Robert Shaw hi-flow 180 degree. Then I replaced the water pump with an Edelbrock hi flow pump. Then I replaced the cooling fan relay with an Ecklers kit that uses the newer style relay. I also bought the optional heavy duty pusher fan that goes in front of the radiator and installed it with an additional relay.
After all this the car would still run 225-235 degrees in stop and go traffic. If I sat for any length of time it would boil over.

Then I read an aluminum radiator loses up to 10% efficency per year. I found a replacement AC-Delco radiator that is slightly larger (the original is .9 inches wide and the replacement is 1.25" wide) for $134. It was easy to replace and fits well, just be very carefull with the transmission cooler lines!

Wow, what a difference. The car does not go over 200 even in AZ 105 degree days with heavy stop and go traffic with the AC on Max! The AC even works better. On 80 degree mornings without the AC, it runs 180 degrees. It will creep up to 185 at a stop light and immediately cool down when i get moving.
My recomendation: If you have a cooling problem, first make sure the rest of the system is in good shape, but then just buy the new radiator right off and skip the band aid fixes.

 

My problems were not quite that bad but about 2 years ago I also change my radiator.
I went from .75 inch to 1.25 inch (GM radiator) and had similar success as you. Now I run 195 while driving normal and moving. Creeps up in traffic but comes right down when moving, usually not over 215. Was 98 driving home this week and still OK while driving.

 

....where'd ya get the replacement radiator?

 

GM PARTS DIRECT

GMPartsDirect.com

I know the post going on about them but the few times I have ordered from them I have had no problems. .......Then again I ordered the correct parts so can't comment about customer service.

Paul

 

That sounds like a good deal on that oversized radiator. Glad that the problem is solved and thanks for posting the info.

 

And once it hits 185°, the fan runs constantly, causing needless wear and tear on the fan motor and wasting gas. Not the best of ideas.



That would render my 23 year old radiator, worthless. Interesting. It is amazing that, with my original radiator, my engine runs nearly as cool as yours. Maybe mine doesn't run as cool because my fan rarely comes on. Obviously a new radiator solved this problem, but with proper maintenance, it likely wouldn't have been necessary. Then again, was it the new radiator or the cleaning from in front of the radiator at the time of installation that made the difference?

RACE ON!!!

 

an adjustable thermostatic fan switch mounted to sense the coolant temps on the passenger side of the radiator, where the coolant is returning to the engine, would allow his fan to cycle at, or even below the engine`s thermostat temperature.

it would also shut the fan off when road speed alone was sufficient to cool the radiator...

i use them installed this way on all my vehicles...

 

My 87 Corvette is 20 years old and has been driven every day and has its original radiator, made out of aluminum I might add. My temp at a stoplight on a 90 degree day runs 200 - 205 and drops to the opening temp of my stock 195 thermostat when I get underway. Any radiator not kept clean of debris in its fins and coolant not flushed periodically may lose 10% cooling every year, but mine works just like it did brand new!
The biggest shock to me is that you could buy a thicker radiator from GM for only $134.00 . I think you might have a typo where either the decimal point is in the wrong place or the first digit in the price is incorrect. Which is it?

 

Some of the poster are comparing apples to oranges. The original poster lives in Arizona, a very hot climate. If I lived in Ohio I would have a 195 thermostat. When it's 120 degrees F, you need AC and you need for your engine to stay cool. The fans shut off at about 35 mph. He fixed his cooling system to meet the need of a hot climate. It works for him.

 

The phone number for The Parts Ladi is: 334-493-1240
This radiator is the AC/Delco replacement (Delco # 20461) for 84-89 cars, $134 plus $8.99 shipping anywhere in the US.
It was 108 degrees here yesterday at the airport. Many places in town reported over 113 and some of the other towns here in the southwest reported 118 degrees. My car in stop and go traffic (they shut down I-10 for 3 years while they are widening it!) with the A/C on Max would run 225-240 depending on how much you are stopped and how hot it is outside. Now it stays under 200 in the worst conditions.

This excessively high temerature has contributed to the alternator going out (more than once), the starter going out, and also the A/C was not cooling very well. It has gone through 2 intake gasket sets. The underhood temps got so high it melted one of my relay connectors.

CFI-EFI: Yes, the 185 degree sending unit for the fan may not be necessary with the new radiator. However, I am not sure how much it changes the operation, because when you turn the A/C to Max, the fan runs constantly anyway.

 

Don't be too concerned about the fan motor. They're cheap and easy to intall. When you live in a hot climate, AC and cooler operating temps are more important in my opinion.

PS Ebay has the AC Delco 20461 radiator for $134.00 plus $8.99 shipping. Here's a link http://cgi.ebay.com/ebaymotors/84-85...QQcmdZViewItem

 

Some day some people are going to realize what a thermostat does. Once the stat is open, it is powerless to further cool your engine. If the coolant is at or above 195°, it won't run one degree cooler with a 180° or a 160° thermostat. The thermostat only detemines the MINIMUM operating temperature.



Double check your FSM, as you promised. I believe the road speed fan shut off feature is only in 1990 and up cars.



I know you use your A/C more in Arizona than in most other parts of the country, but 365 days a year? With a 185° fan on switch and a 180° thermostat, the coolant temp will never drop down to the fan off temp. Consequently running the fan constantly. I would think a 205° - 210° fan on temp would still allow the car to run at a reasonable temp with out the wear tear and expense.

RACE ON!!!

 

[QUOTE=CFI-EFI;1560789001] The thermostat only detemines the MINIMUM operating temperature.

CFI-EFI
I think we agree. The thermostat only determines the temperature that coolant is circulated from the radiator into the motor.
The actual operating temperature is determined by a number of factors such as the cooling system efficiency, the engine cooling requirements of that particular combination, and a number of other factors including exhaust efficiency.

The primary problem is most cooling systems are not engineered for our AZ climate. To make matters worse, GM chose to increase the operating temperature (by increasing the thermostat opening temperature) in 1985 in an attempt to lower CO emissions. This combination is deadly and if the engine is even mildly modified, it will not cool suffiently.

Another side to this is the denser the air/fuel mixture, the more power an engine will produce. Colder air/fuel mixtures are denser. In the old days the available engine lubricants forced us to run engines at higher temperatures. Synthetic oils now allow us to operate engines at significantly lower temperatures and actually increase power. On the extreme end of this, most Pro Stocks are packing ice in the radiator just before a run to reduce temperatures.

A side note: I am finding that with ambient temperatures below 85, the electric cooling fan does not turn on.

 

It was before 1985. My '84 came with a 195° thermostat. I think we just agreed that the stat opening temp only determines the minimum operating temperature. A 195° thermostat doesn't reduce the ability of the cooling system to cool the engine sufficiently.



I agree cooler air is more dense and has more oxygen molecules per volume, but the manifold temp isn't all that different while the ricer revving his engine next to you at the stop light in 100° weather with a 160° stat or a 195° stat. Cool your engine between rounds at the strip, but a too cool thermostat isn't going to make much of a power difference in daily use.



Synthetics allow hotter oil temps. Water, acids, and other blow by contaminants don't boil off at any faster or at lower of a temp in synthetic oil, than they do in dino oil.



In other words, your coolant isn't even getting warm enough to activate your 185° fan switch. With a 180° stat, that is borderline too cool. Not as bad as some on here claim, however.

RACE ON!!!