Chevy mechanics- what's wrong?

[Steves32]

My 2003 6.0 cargo van has been overheating somewhat. Has about 120k miles.
Not loosing coolant.
Water pump & hoses replaced 2 years ago.
Seems to be running a bit warmer than normal. This week (mid 90's)- runs cool on freeway, but around town, climbs & drops rapidly- like it has an air bubble in it or something. Twice- I've driven into Home Depot w/ normal temps. Shut off motor & come back 10 minutes later & start it up. Before I get out of the lot- needle nearly pegs & sets off "Check Gauges" light & bell. Fan is running BTW. Within seconds- temp rapidly falls as soon as I'm moving 15-20 mph & back to normal- usually in a time frame of less thatn 5 minutes from starting the van.
No check engine light- coolant levenl in overflow tank at correct level.
What do you think?

 

[Steves32]

Oops- thought I was in Free Parking. Maybe someone can move it.

 

[jerryW]

Sticking T'stat?


jerry

 

[Steves32]

Well- could be....
They usually fail open or closed- usually open.
Plus- when I park at the store & run in for 10 minutes- motor is still warm & stat should still be open.
They replaced it 2 years ago w/ the WP.

 

[purplezr2]

Bad waterpump?

 

[1948]

sounds like a sticky therm to me.

 

[pauldeere]

Does it have an electric fan ? If so is the fan working. I beleive the electric fans run on low speed when the a/c is on all the time, then if engine temp gets high the fans go to high. I have a 2005 chev that has this type of electric fan set up, from the factory....

 

[srmofo]

Bad water pump, slipping fan clutch (if its still mechanical and not electric fan), Does not sound like a sticking t stat to me, possibly a damaged fan shroud but I really dont think so in this case.

Just because the fan is spinning does not mean the clutch is good. Start the vehicle and once its up to temp and the fan is spinning have someone shut it down. The fan should stop almost immediately.

 

[chris142]

Fan clutch?



A partially plugged Radiator will send cool air to the fan clutch which will make it think it's not needed. I'd start by feeling the Radiator for cool spots.

 

[Devildogs]

Go to HF buy one of those temp guns and see whats what. Could even be a bad gauge.

 

[Steves32]

Fan is electric & seems to be running when I checked. Didn't check it when the temp nearly pegged.

Taking it in tomorrow morning- no time to work on it.
I'm a HVAC contractor- time is money.

 

[Mickey O]

Check for a collapsed radiator hose, I had a similar problem years ago and that's what it was, worth a quick check to eliminate it as a cause.

 

[BBDakota]

Sounds like low on coolant or air in the system.

 

[Murphy4570]

Don't rule out a failing temperature sending unit. Those do fail sometimes.

 

[KinzeMech]

If the radiator hose is collapsing, that is likely a restricted radiator.

 

[KinzeMech]

murphy has a good point. Especially if the temp needle is moving faster than the temp could actually change.

 

[RECox286]

Sounds like T-stat to me. Don't settle for less than a Stant no frills of the

correct temp range. I have had bad T-stats right out of the box, and some

only lasted for a little while until I started using the Stant brand. Excellent product

line.

Uncle Bob

 

[Tarheelgarage]

Are you sure it is overheating or just a flaky temp gage in the cluster; not too rare for Chevy's. They typically fail in the full pegged position.

Keep a noncontact thermometer handy and the next time it pegs hot, pop the hood and get a temp reading at the upper rad hose, near the T stat housing.

Post back your results.

 

[Crazy68Dart]

stant or robert shaw. best to bench test them on the stove too.

I would guess stat or radiator plugged. If it was the water pump to do what it is doing would require the impeller to be falling off which is not common. Unless for some unknown reason the serpentine belt is slipping, which I think you would notice different problems (alternator, power steering, etc.).

Could be a head gasket or cracked head, but if you are not actually losing coolant likely not either of those.

 

[oilslick]

I just replaced a thermostat on a van that was just replaced yesterday! It was a 05 with 4.8 mostly the same as yours, couldn't believe it was sticking right out of the box, came in for a water pump and I also did a driver side exhaust manifold,broken bolts! Anyway, the second thermostat worked flawlessly, I was beginning to think the blown manifold fucked up the coolant temp sensor as it was mounted right in front of the exhaust leak but it was the ****** napa thermostat.

 

[superman09]

Sounds like your temp sensor or gauge cluster is dying. If the needle moves almost instantly with a warm motor, like you mentioned with the home depot trips, that sounds more like a gauge problem than anything. The needle should scroll slowly even if it goes from hot water to cold water it should still scroll not jump. Are all your other gauges functioning correctly? If not the gauge check your t-stat then hoses then fans then radiator then water pump. T-stat can be sticky and not frozen, or a hose could be collapsing. Make sure your fans will cycle between slow speed and high speed. When you are up to temp feel around on the radiator and see if you find a spot that is much cooler that is a definite sign of a plugged radiator. Lastly check your water pump, make sure it is spinning and have somebody rev to about 1500 and stick your head under the hood and listen for odd noises coming from the pump (should sound metallic/grindy). When you had all your work done did you/they flush the radiator? If the old pump experienced catastrophic failure you could have pushed trash into your radiator and plugged it up although that typically results in constant warm running not fluctuations. Try the suggestions that have been handed out and let us know what your find, or take it to a shop they should be able to figure it out pretty quick. Good luck

 

[cyamaha2007]

It could be a steam port on the Heads. Ive seen junk plug them up on ls style motors. There should he a crossover tube that connects all 4 ports together and that goes to the rad. It allows trapped air to escape from the heads. http://www.google.com/imgres?q=ls1+...sp=10&ved=1t:429,r:7,s:0,i:97&biw=888&bih=360

 

[Steves32]

Sounds like your temp sensor or gauge cluster is dying. If the needle moves almost instantly with a warm motor, like you mentioned with the home depot trips, that sounds more like a gauge problem than anything. The needle should scroll slowly even if it goes from hot water to cold water it should still scroll not jump. Are all your other gauges functioning correctly? If not the gauge check your t-stat then hoses then fans then radiator then water pump. T-stat can be sticky and not frozen, or a hose could be collapsing. Make sure your fans will cycle between slow speed and high speed. When you are up to temp feel around on the radiator and see if you find a spot that is much cooler that is a definite sign of a plugged radiator. Lastly check your water pump, make sure it is spinning and have somebody rev to about 1500 and stick your head under the hood and listen for odd noises coming from the pump (should sound metallic/grindy). When you had all your work done did you/they flush the radiator? If the old pump experienced catastrophic failure you could have pushed trash into your radiator and plugged it up although that typically results in constant warm running not fluctuations. Try the suggestions that have been handed out and let us know what your find, or take it to a shop they should be able to figure it out pretty quick. Good luck

Needle doesn't jump- it climbs pretty quickly. Did that twice so far in parking lot. I drove it later today, got it to temp & sat in my driveway idling for 15 minutes. Never moved. Turned it off- wait 10 minutes & start the van & watch the temp climb quickly & then start falling as soon as I'm moving.
Most of the time- it moves (not jumping) up & down 20 degrees (approx) at a time.

Radiator could be plugged up. I don't recall if they flushed it before. Original radiator.

I'll know more tomorrow.

 

[redwrench60]

You have an air pocket or low coolant level in radiator. Do you hear any "gurgling" behind the dash while accelerating?

 

[38Chevy454]

Sounds like an steam/air pocket. When you shut off the engine, some latent heat and lack of coolant circulating allows a small steam pocket to form. That steam prevents coolant from reaching the thermostat. The thermostat stays closed, then once small amount of coolant finally reaches the thermostat it can open and the temp returns to normal.

I am not an LS engine expert, but it does sound like you have the steam tube/ports clogged up as suggested. If you can't fix the steam ports to flow open, you could drill a small hole around 3/16 inch in the thermostat to allow the steam/air to escape. This will prevent the temp spiking.

I have this same temp spiking problem on my old 97 Expedition. But it is caused by a slight leaking head gasket and when it is warming up, the combustion gases get into the coolant and prevent the thermostat from working. Causes the temp to spike and then when it finally opens the temp returns to normal. Since I am not going to fix the leaking combustion gases due to head gasket or other such as crack, I just drilled a couple holes in the thermostat and problem went away. Yes it takes a bit longer to warm up and on really cold days the heater is not so hot as before. But I figure better to not have the engine briefly overheat constantly. Once warmed up the combustion leak is sealed and do not experience more leaking, otherwise it would be a problem that needs to be dealt with correctly instead of band-aid fix. I do have the gurgling water sound in my heater core due to it being the high spot in the coolant system. The holes in the thermostat allow the steam/air to circulate out and the gurgling goes away, and the heater works.

 

[Steves32]

You have an air pocket or low coolant level in radiator. Do you hear any "gurgling" behind the dash while accelerating?

No gurgling sounds I can hear. I crawled under it this morning & looks like WP has leaked at some point from weep hole. Nothing on ground though.
Overflow tank is full- I'm wondering if there's an issue w/ cap or something where radiator is low on coolant & being a closed system- not drawing the overflow coolant back to radiator?
We'll see. Dropped off van at my friends shop 30 minutes ago.

 

[Steves32]

UPDATE!

He just called me & found several things of interest.

>Water pump is leaking & needs replaced.
>Coolant in radiator is low- maybe restriction/crud in overflow tube or cap.
>Coolant looks like mud. Radiator needs flushed.
>Replace thermostat just because.
>Replace rad cap
>Fan clutch is history. Fan clutch? Shows how stupid I am. Here I thought it was an electric fan!

Estimate is $558.00 P&L
Sounds good to me! I hate working on newer stuff.

I told him to replace hoses if needed too.

 

[redwrench60]

Great!, glad it wasn't something outlandish or hard to diagnose.

 

[Steves32]

He said most of my issues were the fan clutch, since it cooled fine at speed.

 

[BigE]

Doublecheck your water pump. It may be fine. They used o-ring gaskets behind them from the factory and the o-ring will separate from the metal gasket. If the o-ring is orange, it is original and most likely failed. The new design uses a black o-ring on the aluminum substrate. At 120k miles, you can make the call to replace the water pump anyway since you have to remove it to fix the gaskets. However, when I priced one, the best I could do was 140 bucks for a quality replacement. My truck only had 60k miles so I chose to reinstall the original.

 

[KinzeMech]

UPDATE!
Estimate is $558.00 P&L
Sounds good to me! I hate working on newer stuff.

For a pump, t-stat, fan clutch, coolant flush (and coolant, presumably?) that is a good price. Especially if it includes the diagnosis that's already been done.

 

[Murphy4570]

That's a good price for all that work.

BigE, replacing the waterpump on cars when doing a waterpump gasket is SOP with the vast majority of shops, just to prevent comebacks. I have seen more than one waterpump fail because the front seal starts leaking, or shaft bearings go bad.

 

[Steves32]

For a pump, t-stat, fan clutch, coolant flush (and coolant, presumably?) that is a good price. Especially if it includes the diagnosis that's already been done.

That's correct. He's very fair & I trust him. I've used him for 15 years for my auto a/c & rad work.
I wouldn't crawl all over that motor for that price. He was done by 1pm- runs perfect, nice & cool now.

 

[Mr.Magoo]

These guys are pretty good over here about getting you what you need. And those speaking about air in the coolant, low coolant are probably GM mechanics. GM has had some problems with some engines that have the cross-over tubes, the o-rings and also getting air in the cooling system. Some people chase everything only to find out that it may be one of the three or something similar. After losing coolant it is imperative to get all of the air out of the system. Look on the net at auto forums and you will see many postings about this stuff. One guy even jacks his car up from one side to bleed the air after slowly filling with coolant. Anyhow, at the cost of labor, I hope they get it right the first time.. Good Luck,,,, I had similar problems, got it fixed and sold the piece of S#@! Impala

 

[cgall]

Before I payed for all that I would have started it up cold and take the rad cap off and let it heat up until it starts to boil over. The hole in the thermo works good, too.

 

[joe (pa)]

I'd check the fan clutch

 

[KinzeMech]

Why is it so much harder to burp cooling sytems today?

I've driven a lot of vehicles with a good old fashioned Gen1 small block chevy, and if you got air in those systems all you had to do was fill it up today, drive it, fill it again tomorrow, and you're done.

I'd give anything to have a radiator with a cap on it again...this put the fill cap only on the expansion tank **** that almost everyone does today is BS.

 

[Steves32]

I'd check the fan clutch

They replaced the fan clutch

 

[bgott]

http://www.tooltopia.com/uview-550000.aspx