Operating Temp Concern!

cwarrenburgess · May 25, 2009

I have a 1993 Suburban with the 7.4 454. My concern is this. When driving my vehicle in the morning or evening during cooler temps, my operating temp is anywhere from 180 to 200 consistently and slightly lower when I'm on the freeway. However, during the higher temps in the middle of the day, the operating temp jumps up to 210-220 when I'm NOT running the a/c and 220-250 when I AM running the a/c. The temps climb rapidly when I am in traffic or idling and only subside back to the 210 range when I get up to about 40mph plus or get on the freeway. At that point, they drop back to 190-210. When parked and running the a/c, I can get the temp down by increasing my rpm to 2500 and then it only drops slightly to 220.

I have heard the 454's run hot, but this seems unusual. I have replaced the fan clutch, the serpentine belt and flushed the cooling system as well as removed the thermostat. I do live in the desert, where the temps will routinely reach 110-115 during the summer. Could it be the water pump? Is my radiator too small for this region? Should I add 1-2 electric auxillary fans to the front of the radiator? I am fearful I may burn up my engine if this continues...help!?!

txab · May 25, 2009

Did the new fan clutch make any difference at all? Have you checked to see if the temp that the gauge is displaying is accurate? Are the condenser and radiator clean of bugs and debris? You say you flushed the system, have you checked for partially blocked radiator passages?

bill190 · May 25, 2009

I would get a new radiator and if you can, a larger radiator.

There are little passages inside a radiator for the coolant to flow through it, and over time, some of these passages get blocked/clogged. This makes it as though you have a smaller radiator.

With a new radiator all of these little passages are open and water flows evenly throughout the entire radiator surface, thus you get maximum cooling.

Below are two pictures of the little holes inside a radiator. The first picture is an old clogged radiator and the second picture is a new not clogged radiator. The coolant flows through the little holes from one side of the radiator to the other, but if the holes are blocked, less water will flow through it. Or if some areas are blocked, this effectively reduces the "size" of the radiator.

Old clogged radiator...

Not clogged new radiator...

superjim · May 25, 2009

yes...250 is definitely too hot.

I would think about a new, high capacity radiator or having the one you have now..RECORED.

If I was going the recored route, I would have them add one more core to it if at all possible.

The older 454 radiator is a three core...but the tanks are capable of being 4 core.

I have had a couple of 454's that I had to do that to, to keep the temps stable in hot weather.

Adding the extra core increases the cooling capacity of the radiator a lot.

Your other option is adding an electric fan in front of the radiator.

Crazy Canuck · May 25, 2009

I have a 1993 Suburban with the 7.4 454. My concern is this. When driving my vehicle in the morning or evening during cooler temps, my operating temp is anywhere from 180 to 200 consistently and slightly lower when I'm on the freeway. However, during the higher temps in the middle of the day, the operating temp jumps up to 210-220 when I'm NOT running the a/c and 220-250 when I AM running the a/c. The temps climb rapidly when I am in traffic or idling and only subside back to the 210 range when I get up to about 40mph plus or get on the freeway. At that point, they drop back to 190-210. When parked and running the a/c, I can get the temp down by increasing my rpm to 2500 and then it only drops slightly to 220.

I have heard the 454's run hot, but this seems unusual. I have replaced the fan clutch, the serpentine belt and flushed the cooling system as well as removed the thermostat. I do live in the desert, where the temps will routinely reach 110-115 during the summer. Could it be the water pump? Is my radiator too small for this region? Should I add 1-2 electric auxillary fans to the front of the radiator? I am fearful I may burn up my engine if this continues...help!?!

Why would you remove the thermostat? The job of the thermostat as I understand it is to keep the engine at a consistant temperature. I would replace the thermostat, but I don't think I would ever remove it.

georgecdisc · May 25, 2009

Why would you remove the thermostat? The job of the thermostat as I understand it is to keep the engine at a consistant temperature. I would replace the thermostat, but I don't think I would ever remove it.

Perhaps removing it is a test to see whether the termostat is being problematic, ie it is closed when it should be open.

superjim · May 25, 2009

Why would you remove the thermostat? The job of the thermostat as I understand it is to keep the engine at a consistant temperature. I would replace the thermostat, but I don't think I would ever remove it.

Perhaps removing it is a test to see whether the termostat is being problematic, ie it is closed when it should be open.

Both of you could be right, but like Crazy Canuck, I would replace the thermostat.

Thermostats are made not only to regulate the temp of the motor for efficient operation, but to a certain extent to SLOW DOWN the coolant circulation so that the coolant can absorb heat from the engine and the coolant needs to STAY in the radiator long enough to also DISSIPATE the heat it picked up when it was in the engine.

If the coolant flows thru the engine too fast...it never has time to actually COOL OFF when it is in the radiator.

Back in the old days...I took the thermostats out of a few cars, figuring they would run cooler...they would around town at low rpm.

At high rpm they would actually run HOTTER than when the thermostats were installed.

rjirvine · May 25, 2009

I would definitely put the thermostat back in as a minimum. I had a 1988 K1500 and when I visited Las Vegas one summer I had the same problems as you. The problem was a thermostat that was rated too low (I lived in Seattle at the time) and in that heat, the thermostat would open and basically never close when it was 115 degrees outside because the system couldn't cool it down enough.

With the thermostat missing (or always open), the fluid in the radiator can't cool down, so all of your coolant will heat up.

That may not solve your problem, but it will be a place to look. I would use a 195 degree (there's 3 for your engine I believe, 160, 180, 195). Your system should be able to cool to 195.

Also look at your radiator cap, it my not be holding rated pressure, and they're cheap to replace.

As you probably know, the coolant will boil sooner when the pressure is below the rating of your cap, and also if there is more water than 50%.

If that doesn't work, I would look at the possibility of clogged radiator passages, then water pump.

I hope this helps!

PS: For the love of god, make sure you don't put the new thermostat in upside down (backwards)

Crazy Canuck · May 25, 2009

Why would you remove the thermostat? The job of the thermostat as I understand it is to keep the engine at a consistant temperature. I would replace the thermostat, but I don't think I would ever remove it.

Perhaps removing it is a test to see whether the termostat is being problematic, ie it is closed when it should be open.

Could be. Usually when they are stuck fully closed, they overheat pretty quickly in warmer ambient temps. If I have ever suspected a problem with the thermostat, I usually just replace it as cheap insurance.

cwarrenburgess · May 27, 2009

I had removed the thermostat in order to confirm it was indeed not working, which to some extent it wasn't. I left it out hoping the vehicles operating temp would remain lower for a longer period of time. I will reinstall the thermostat asap. I have a new one rated at 195 degrees.

My new fan clutch is definately engaging during higher operating temps. Sometimes it sounds like a jet taking off at McCarran! It has seemed to help, but my idling and in-traffic temps are still definately too high.

I will look into a larger, 4 core radiator this week as well. I am the truck's second owner. The vehicle was originally sold in San Francisco. This is it's first year in Vegas, and a lot of things are beginning to come to light with this heat.

Thanks a million for everyone's input. I will put it to good use!!