Truck temperature fluctuates

[JetMech]

So my 04 Dodge Ram hemi has had this issue now for while. When the truck is at operating temp and in cruising down the 215, whenever I romp on the gas momentarily (2-3 seconds) to pass someone or to just hear the hemi, I have noticed that the temperature will increase about 3-4 needles width on my gauge. I just replaced the radiator and the thermostat with factory replacements. I took the hot tod tune out and put the stock one back in. With this configuration, the problem still exists.

My only logic is that the water pump is worn and can't keep up with circulating enough water through the engine with the added heat from high RPM operation. It can keep up at highway speeds which is probably why it hasn't overheated.

Any input would be appreciated. And I did burp the system after I installed the radiator today. My concern is traveling up the passes between here and SoCal with the bike and la familia loaded up.

[got2go]

Any issues on city streets?
From stoplight to stoplight?

Take out the thermostat if you can, and try the same thing and see of the temp fluctuates the same.

[JetMech]

Temp will increase 1 width at a drive through then back to normal after I get going.

Bad radiator cap?

[tomy]

If the water pump is not weeping, the pump is still good. bad cap will do that.

[Rev. That Guy]

bad cap is possible, but since you said that you recently changed the rad, did you fully bleed the system? most of the time it will work its way out, but some vehicles, especially GM vehicles, are prone to air bubbles causing wild fluctuations in temperature. You can pick up a new cap for a few bucks. also, you can get a cap with a pressure relief lever on it. this can be used to help bleed the system.

Check your T-stat as well. I have seen on more than one occasion that t-stats fresh out of the box can be bad. If its not too much of a pain in the ass to get to, pull it, and throw it in an old pot and stick on the burner and watch to make sure it functions as it should. It should open well before boiling point (depending on your factory temp settings for the t-stat, usually in the 190 range).

The problem with cooling systems is that all of the parts HAVE to work or none of them do.

Definitely check for air though. Some vehicles have bleeder valves in the system, usually on the t-stat housing. If not, you can simply, with a cool motor, pull the rad cap off, start the vehicle and let it run up to temp until the t-stat opens and "burp" the system. Alternatively, use the pressure relief cap i mentioned above. Another thing to check would be for any leaks in the coolant hose that runs to the res tank. If this has a hole, it may be sucking air in when it cools. If you go with the cap method (with the lever) let the engine get up to temp, shut it down, lift the lever to relieve pressure (and hopefully any air that would have risen to the cap as its the highest point in the cooling system usually) then once it cools and contracts, it will draw in new coolant from the res tank.

A water pump can be bad and not weep, seep or anything else. dont rule it out, but again, in my experience, when pumps go out, it is usually catastrophic or complete failure. there isnt really much to wear out.

Try those things first as they are the cheapest and easiest. After that, you may need to do some further investigation if that didnt fix the problem.

Any obstructions over the radiator? sounds stupid and simple enough, but you never know.

- J

[Rev. That Guy]

sorry, missed the last line of your post...

try burping it again. If you are unsure, give me a shout and bring it by and i'll have a look. You likely have a bleeder somewhere.

Air will heat up far faster than the coolant will and will get hotter too so this is why i suspect that.

- Justin

[LVNeptune]

Might have a slightly leaking head gasket. Have you checked oil lately? Ran a compression test recently?

[JetMech]

Just did an oil change. No water In the oil and the coolant looked good. No debris or rusty colored stuff. I used my old radiator cap. I will buy a new one on my way to work I the morning and replace that right away. From what I gather here, many of you are saying air in the system. I will try the cap and also burping again to see what happens.

I noticed this start to happen after I replaced my first thermostat. That one lasted about 6 months then replaced it. Only reason I replaced radiator was because it developed a leak in one of the tanks.

[Rev. That Guy]

my money is on air in the system. Again, look for a bleeder somewhere around the t-stat. Looks just like the bleeders on your brakes. get it up to temp then CAREFULLY bleed the system through the bleeder. use a tube or hose if you can to direct the hot stuff away. If not, put a folded rag over it and use a long wrench so you don't burn yourself. Hot coolant WILL come out and if air comes out, it will be even hotter. Hot enough to ruin your weekend anyway.

Good luck and the offer to help still stands.

- Justin

[got2go]

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