I have a 72 Cutlass that had an Olds 403 put into it about 15 years ago. She warms up to 200 and never drops below that. Stays between 200-205 most of the time but when sitting still with AC on she will get to 220 (I turn off ac at 215). I am more accustomed to Chevy 350’s so I don’t know if this is a normal oppressing temp.

it seems to me like the thermostat in there is a 200 degree thermostat. Thinking of putting in a 185. Thoughts? Ideas? Thanks in advance for the help!

 

Sounds like factory temps. You probably have a 195* thermostat. Remember that coolant under pressure doesnt boil until 255* or so, so 220* is not overheating. Changing to a 185* Thermostat will just open the thermostat sooner, but may not lower your peak temp.

 

What are safe operating temps for an olds 403? I know on a Chevy 350 that 230 is overheated.

 

Probably still the factory 195 thermostat, try a Robert Shaw 180 high flow. What radiator, fan and does it have a shroud? I would consider 230 overheating as well. The 403 is like a sbc 400, siamese bore and tend to run hot. I had endless overheating issues with one in my 88 Cutlass. The fix for that car was the GN rad surround. My 70 Cutlass S with a 9+ to 1 403 never gets above 190, 160 Robert Shaw high flow thermostat, Flowkooler water pump, big 1 1/8" dual core aluminum radiator with Dodge Stratus electric fans.

 

How did you get those temperatures? An IR thermometer or coolant temperature gauge? If it was a gauge was it name brand or a parts store cheapie?

 

from an Auto Gage brand coolant temp gauge.

 

The way I look at it there isn't a single point where the temp is suddenly too hot. Rather it's a gradient. Everything should be pretty happy and running well at 180, starting to get sweaty at 200, I get a bit worried at 210, then I start looking for places to stop or something to change at 220, and shut down if it hits 230. Over 230 starts getting really hot and things can have problems.

If you don't know what thermostat is in there then first step is always put in a known one. I like the robert shaw ones as well, but they can be hard to find sometimes. And make sure the fan clutch (if equipped) is engaging correctly, radiator is clean, coolant is in good shape, water pump is pumping, etc. Make sure your radiator is appropriately sized. I got away with an aftermarket 1 row aluminum (e.g. CU161) rad for a long time, but once I started having more fun with my builds that just wasn't enough.

The 403 is a thin wall block, so it will tend to run hotter than a similar Olds 350 or 455. So whereas with a 350 I would expect to keep the engine at 180 to 190 pretty much regardless of what's going on, with a 403 I was normally running closer to 200.

 

Excellent!!👍

If you change the thermostat make sure you test the new one before installing. Ask me how I know.

 

I run a 180 in Houston on a stock 403 with AC. I recently had to replace the fan clutch and with the HD clutch working and a 180 t-stat I had A/C in stop and go traffic and the temp gauge is MUCH lower even in triple digit heat and traffic.

I had similar issues, but my fan clutch was bad, now it sounds like hurricane and pulls a towel to the grill nicely.

Edit to add:
My factory temp gauge shows 210 in the middle and 100 and 250 left and right of that.I also did what I could to drop the heat when it moved much past 210

 

It never ceases to amaze me the misinformation and the old wive’s tales that are out there about engine operating temperatures.

Here’s a few key facts.


1. There is nothing sacred about 200F. An engine can operating perfectly normally at 210 or 220. Way back in the day, I had a ‘75 Chevy Nova with an in-line Six, and one of the first things I did, just for the heck of it and because I was a high school kid, was install a temperature gauge. That thing registered 220 the first time I used it, and it registered 220 for the next 10 years when I finally sold the car.

I assumed the car was running normally when I installed it, so I assumed that whatever temperature it registered the first time I used it was normal. If it got significantly higher, I would have looked into it. It never did. As has been pointed out MANY times in these forums, at pressure, coolant boils at 250F. 220 is WAY below that.

I know the Chevy Six is not an Olds V-8 and yadda yadda yadda. It's still an gasoline-fueled internal combustion engine.


2. What thermostat is installed DOES NOT MATTER. The thermostat controls when coolant it sent through the radiator. The higher the temperature rating of the thermostat, the hotter the engine has to be before the radiator kicks in. This is GOOD, not bad. Engines operate most efficiently the higher the temperature. This is a thermodynamics thing. So the faster the engine gets to operating temperature, the better. Choice of thermostat does not affect final operating temperature. It affects only how long it takes to get there, and getting there slowly is not good.

My two Oldsmobile Toronados with a 403 engine have 195 thermostats, and that’s what the service manual says should be in there.

3. As a corollary to #2, thermostats are not put there so that the occupants can have heat faster. They are there to allow the engine to warm up quickly.

4. Engines can be harmed if they operate at too cold a temperature. Combustion is inefficient, Unburned by-products build up. Fuel mileage decreases. There is no such thing as if 190 is good, 180 is better, and 170 is better still. What the heck. Why not strive for operating at room temperature?

5. There is a reason why service manuals do not specify what a typical operating temperature is. It can vary depending on all sorts of things. The HOT light sensor is set to light the dash light when the engine temperature reaches some high value, like 230. Maybe higher. The point is, there is lots of leeway here, and it would do no good to try to set the sensor to trigger the light just above some “desired” value and then list that as the specified operating temperature.

6. The worst thing that many people can do is install a temperature gauge. Prior to that, if the idiot light didn’t turn on, they went about their lives blithely unaware of what their engine’s operating temperature was. The car ran fine, and they didn’t thing twice about it.

Then they put in a temperature gauge, and all hell breaks loose. They see the temperature creep up to 200 or so and get spooked. They suddenly think something’s wrong, they go and buy IR sensors, and they start posting on here about their overheating engine, They’re afraid to drive their car, and and their life becomes miserable. The solution is to remove the gauge!

 

To expand on jaunty's point 2, when your engine temperature gets to 220, your 195° thermostat is open. If you put in a 160° thermostat, that would also be open when your temperature gets to 220. The thermostat has no material effect on your stated problem.

Your problem correlates with poor air flow through the radiator, or inadequate radiator capacity.

 

X2 on Jaunty's entire post. With a 16 psi radiator cap, coolant boiling point is over 250 F. Engines run more efficiently at higher temps. Your radiator also transfers heat more efficiently when the temp difference between the radiator and the air is greater.