Fluctuating Engine/oil Temperature

[NFSGamerUSA]

In the past week or so (once it really starting getting around 50 degrees Fahrenheit or below) my temperature gauge has started fluctuating quite a bit. Tonight it nearly reached the 3/4 mark between 210 and 270, I guess about 230-235 and soon after went all the way down to the 1/4 mark between 100 and 210 (roughly 160-170). Any idea what the issue could be? It's running fine, but that gauge was scaring me. I read some stuff that said it's the cooler coolant from the radiator and the warmer coolant from in the engine being cycled around, but do you guys think that's the case? Do you think it could be the thermostat acting up? Thanks!

[jrrod2004]

In the past week or so (once it really starting getting around 50 degrees Fahrenheit or below) my temperature gauge has started fluctuating quite a bit. Tonight it nearly reached the 3/4 mark between 210 and 270, I guess about 230-235 and soon after went all the way down to the 1/4 mark between 100 and 210 (roughly 160-170). Any idea what the issue could be? It's running fine, but that gauge was scaring me. I read some stuff that said it's the cooler coolant from the radiator and the warmer coolant from in the engine being cycled around, but do you guys think that's the case? Do you think it could be the thermostat acting up? Thanks!

 

check your thermostat to see if it is working properly...

[shadaytree]

my buddy from long island told me about this on his truck once. i dont think he did anything and it eventually fixed itself. but that could be an expensive gamble. i would do the same as mike.

[NFSGamerUSA]

Yeah, I'm 100% for playing it safe instead of being sorry, so I'll be getting to the bottom of it. I, too, thought it sounded like the thermostat, but I found differing explanations on Google and decided to ask here to see what you guys think. I forgot to look at the gauge much today, but when I finally remembered it seemed like it was running the consistent, normal operating temperature without fluctuating. I'll see what my neighbor thinks about it if it keeps doing it. Thanks for the replies!

[98 Z71 SLT]

I think you are low on coolant. Was it you, a few weeks ago, looking for an answer of a coolant leak??? Maybe, maybe not. Check your intake gaskets and coolant pump.

 

But first, with a cold engine, remove the radiator cap and look down your radiator. I bet you'll be low on antifreeze...

[NFSGamerUSA]

I think you are low on coolant. Was it you, a few weeks ago, looking for an answer of a coolant leak??? Maybe, maybe not. Check your intake gaskets and coolant pump.

 

But first, with a cold engine, remove the radiator cap and look down your radiator. I bet you'll be low on antifreeze...

 

No, that was someone else. I have no leaks, at least not externally (and I certainly hope none internally). How much antifreeze should I have, up to the bottom of the filler hole? I looked in there the other day after I started having this issue and it was an inch or so below that, but I didn't think it was overly low, or low enough to cause a problem. I do plan on getting a little more coolant, at least if necessary.

 

EDIT: I just checked again and it's VERY low. I was deceived when I checked a few days ago; the engine must have been warm or something. So do I need to pick up that Dex Cool shit or can I use regular coolant? Will a gallon be enough for a 50/50 mix?

 

RE-EDIT: I found specifications that list 18 quarts (4.5 gallons) of coolant, is that correct? Also, since I have nearly 141k, do you think I should go ahead and completely drain the coolant in the system and replace it with fresh coolant (from the same location it says it should be replaced at 150k)?

[KillerKnife]

I think you are low on coolant. Was it you, a few weeks ago, looking for an answer of a coolant leak??? Maybe, maybe not. Check your intake gaskets and coolant pump.

 

But first, with a cold engine, remove the radiator cap and look down your radiator. I bet you'll be low on antifreeze...

My fist thought is low Coolant. I have been one of about 4 in the past couple of weeks with a thread about coolant. This is first how I noticed the problem was spiking temps. And then looked like my oil was decreasing ever so slowly.

[NFSGamerUSA]

Yeah, it's low on coolant, see above.

[mipsco1]

for the price there is no reason not to do a rad flush and if u are already draining it change the thermastat. I would do that first because of how cheap it is and it will either fix it or eliminate two maybes

[NFSGamerUSA]

Well, more coolant is urgent (I plan on getting some tomorrow once I find out what to get and how much), but I'm not sure if I'll be able to get a thermostat unless they carry the correct one at AutoZone.

 

EDIT: Nevermind, I think they have some thermostats, although I'd prefer an ACDelco thermostat which they don't seem to carry. Should I replace the cap, as well? I guess that coolant had to go somewhere, and it must be slowly leaking in the intake or out of the pump as suggested, so I'll check that tomorrow before I go to get the coolant and thermostat. The oil is clean and I've never seen any puddles or stains under my truck.

[98 Z71 SLT]

1. With 141k on it, has your intake manifold ever been off?? If NO, I can pretty much guarantee that is where you are losing coolant. Inspect VERY closely. You'll see coolant traces at either the front side of the engine block, OR you'll see coolant traces (stains) on the trans bell-housing, which both would indicate your intake gaskets are toast. Not a bad job at all to do...if you've worked on Small Blocks before, this is a walk in the park.

 

2. Also, check your passenger carpet. Is it wet/sticky? If YES, then your heater core is leaking, and needs replacement. Another common complaint of this would be "foggy windows" and "sweet smell" from dash vents.

 

3. Inspect radiator and water pump. Look for traces of a leak.

 

4. Also, check the heater core adapter fitting, located at the passenger front corner of the intake manifold. Make sure it isn't cracked and leaking coolant.

 

Number 1 is most likely...let us know...

[NFSGamerUSA]

1. With 141k on it, has your intake manifold ever been off?? If NO, I can pretty much guarantee that is where you are losing coolant. Inspect VERY closely. You'll see coolant traces at either the front side of the engine block, OR you'll see coolant traces (stains) on the trans bell-housing, which both would indicate your intake gaskets are toast. Not a bad job at all to do...if you've worked on Small Blocks before, this is a walk in the park.

 

2. Also, check your passenger carpet. Is it wet/sticky? If YES, then your heater core is leaking, and needs replacement. Another common complaint of this would be "foggy windows" and "sweet smell" from dash vents.

 

3. Inspect radiator and water pump. Look for traces of a leak.

 

4. Also, check the heater core adapter fitting, located at the passenger front corner of the intake manifold. Make sure it isn't cracked and leaking coolant.

 

Number 1 is most likely...let us know...

 

Well, seeing as I picked the truck up with around 137k miles, I haven't replaced the intake gasket and have no idea if it's been replaced. My passenger side carpet has always been damp (but not sticky), and I've never figured out what it was, but now I know. My windshield does build up a fog/film on it over time, and at first I thought it was the Armor All I had put on the dashboard and stopped using it, but it again built up a film and I haven't put anything on the dash besides window cleaner in months. Sounds like a nice, new can of worms that I'm getting into, as I wouldn't be surprised if just about all of these things are contributing to the problem...

 

How difficult is it to get to/replace the heater core? The water pump isn't too difficult, is it?

 

I'm going to go outside again and see if I can find anything with a flashlight so I can try to find out what might need to be replaced. I'm keeping my fingers crossed that it's not as bad as I expect.

[98 Z71 SLT]

Well, on the info you just provided, I'd be planning on doing the Intake gaskets (for-sure) and checking the heater core area for any signs of a leak. You can check under the dash on the passenger side...the black HVAC case will be wet if the heater core is leaking....

[NFSGamerUSA]

I'm not sure if the heater core is an issue, actually. You see, it gets wet UNDER the mats, so I'm pretty sure it's not coming from something that's dripping. It's not wet right now (although the bottom of the rubber mats felt just slightly moist), and I haven't checked for dampness in a long time. When it was wet/damp, it was around the middle of the floorboard. It's never been wet on/near the carpet edge under the dash, either.

 

I can't find any trace of leakage near any of the pullies, so I guess that's a good sign. Same for the tranny bell housing. From what I could tell and feel, there wasn't any wetness around the intake manifold, but the edges did look like they had been moist more lately than the rest of the engine considering the dirt was a little darker around the edges. I guess, and hope, that it's just the intake manifold gasket.

 

I'll go ahead and get coolant and a new thermostat (What about a radiator cap?) from AutoZone tomorrow, I suppose. I guess I'll completely flush out the system. Now, will this be and issue when I replace (or have replaced) the manifold gasket? As in, will I need to drain the coolant in order to remove the intake manifold? Yes, as you can tell, I've never worked on a real engine, but I can receive adequate help from someone with experience since it's an easier job.

 

Getting more specific about the flush, will I need Dex Cool or can I use regular coolant since it's a GMT400? Does the system hold 18 quarts/4.5 gallons on coolant?

 

Now I did forget to check under the radiator itself, but I'll check tomorrow and see if there are any traces of a leak from that location. However, if it were leaking from the bottom of the radiator, wouldn't I find puddles or stains under my truck since it's not in a location where the heat would evaporate it off?

 

Thanks a lot for the help!

[NFSGamerUSA]

Sorry to bump, but I need to know what coolant to get tomorrow (i.e., Dex Cool junk or regular coolant). Also, is there a specific radiator flush solution I should use (I'm going to flush what's in there out and put in fresh coolant)? Thanks!