2002 Sonoma Heating/Cooling Problem


Old 10-09-07, 10:25 AM
Thread Starter
Join Date: Jan 2007
Posts: 58
2002 Sonoma Heating/Cooling Problem

I have a problem with the heat/cooling system in my 02 Sonoma (v-6). The heat works OK until the gauge reads about the middle (works fine as the truck is warming up from a coldf start) But... once it gets to about (the gauge reading anyway) 210 deg, the heat stops heating, it gets cold. Then, the engine temp, while driving at the same speed, engine load etc, drops offs 20-30 deg and it stays cold. Once I stop and the truck cools off, its OK until the process repeats.

This morning, the check gauges lite (not check engine) came on and low and behold the temp was peaking towards the high end of the scale. I put the thing in neutral and coasted down the hill I was on and pulled over. I let it run for .. maybe one minute , probably less and, the temp went back to 'normal': normal being where it had the drop off to the 180 range.

The heat still did not work.

In the past it was quite fine and steady at about 200-210 deg (on the gauge) with the only deviation being under heavy or light load, as I would expect.

Is this as simple as a thermostat ? Or is there some other (which would be sure to aggravate me) electronic problem. I sure would appreciate any inputs.

I will probably just change out the thermostat (I have not looked at it yet so I hope it is accessible)

This thing has only 60k miles on it and never again... no more Chevys, no more GMC no more American. I have fixed too many never-should-break items on this 'gem'.

Now I feel better;; so if there are any ideas I would appreciate the input


Last edited by bobfoley1276; 10-09-07 at 10:35 AM. Reason: Title incomplete
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Old 10-09-07, 10:44 AM
Join Date: Sep 2007
Location: wisconsin
Posts: 73
sounds to me like i is low on antifreeze and is getting airlocked i would check the level and check the ends of the intake gasket for coolant leaks
Old 10-09-07, 04:35 PM
Join Date: Feb 2005
Posts: 579
I second that. Post your findings please.
Old 10-10-07, 04:50 PM
Thread Starter
Join Date: Jan 2007
Posts: 58
GMC Sonoma Coolant Problem

Absolutley right... low antifreeze. Aggravating but I think I understand 1/2 the issue.

The over flow bottle is not at the right level but..... there is a reasonable amount of fluid in there. So.... I opened the radiator and it was down....oh.... 4-5 inches.

I bought some Texaco antifreeze, supposedly GM Dexcool compliant, at least thats what the jug indicates, its red if nothing else....

So: the owner's manual, which I cracked open for the first time in 5 years says: if you have to add coolant MORE than 4 times a year, have the system checked. HUH ??? Does this thing use coolant somehow ? Is it expected to leak ?

I can understand the overflow bottle not empyting back into the radiator if the cap is messed up or if the radiator has a leak in it. But I dont see any leaks anywhere (external or internal, based on recent oil change)

I never had a problem for five years and while I have not examined real closely, I dont see any puddles under the truck. I changed the oil a few weeks ago and the oil was OK, actually quite good (first time I used a batch of synthetic oil, changed at about 4500 miles). I didnt see any leaks as I spent a while underneath lubing the front end.

So I guess here's my next set of questions (by the way, the addition of about 2-3 quarts of Dexwhatever solved both problems: over heating and the lack of heater). Ques 1: Where did the coolant go ? Is it possible it got really hot in the summer and overflowed as I was high speed driving ? Did that for 8 hours in August on I95 to Maryland from Mass. back and forth I havent had the heater on since last April here in Mass so I dont know when it stopped working correctly.

Ques 2: If its leaking internally, wouldnt I see some frothy or white oil ?

Ques 3: If its leaking externally, I would think I'd see some puddling or if it were dripping onto the exhaust I would smell it ?

OH well, we'll see what happens now thats its refilled. Like the manual says...dont worry, so long as its less than 5 refill times a year !

By the way: At less than 40K miles had to change the dist cap, when ever it rains, the rain washes the grease off the door hinges and you have to regrease the roller on the drivers side hinge, the front wheels throw up mud into the door opening, but GM did install 3 redundant seals at the bottom of the door, I had the side door latch break after I had the truck about 6 months, the heater/defroster diverter broke inside the heater (warranty repair that was written up for over $400 repair cost), I have had to change out the parking brake pads....god knows why but the parking brake would not hold and I could not adjust it. The brake rotors just about rotted away with less than 50k miles, the emergency brakes cable has worn through because of mis location at the factory. If there is snow or rain on the roof, you find out real quick when you open the door: it pours onto the truck and onto the door with its electrical switches. The oil filter access door opens only enough so you guarantee dumping oil all over when you change the filter. I can't wait to see what happens when the speed sensitive radio volume breaks. .......Its probably tied into the ignition system......

General Motors , you listening ? I would rather have reliabilty than speed controlled radio volume.

Anyway, thats where I am .. Thanks for the input. It verified what I found last night.
Old 10-11-07, 07:40 PM
Join Date: Sep 2007
Location: wisconsin
Posts: 73
i would guess that if u look at the corners of the intake u will find coolant leaking just not enough where you are seeing puddles
Old 10-16-07, 04:30 AM
Thread Starter
Join Date: Jan 2007
Posts: 58
Sonoma cooling

I looked at the engine pretty closely and I cant see any leaks. this truck has an iron intake so I am not thinking it ought to leak.

But I'll keep an eye on the level and see what happens
Old 11-15-07, 10:31 AM
Thread Starter
Join Date: Jan 2007
Posts: 58
Sonoma Coolant Leak

I guess I found the problem. It seems like there is a leak, not on the manifold itself, but where the fitting (metal) bolts onto the manifold near the front. I would describe it as where, in the old days, the thermostat used to be located connects to a hose that goes to somewhere (the radiator?)

I checked the bolts for looseness and they are tight so I guess the sealant at the interface gave up the ghost. It does not look like this fitting has a gasket. Its not leaking much and I think the only reason I found it was I must have looked at the right time. I think most of the escaping coolant evaporates on the block so it was tough to see a leak.

Anyone know the approriate sealant/gunk to use if this does not have a gasket ?
Old 11-15-07, 08:30 PM
Join Date: Nov 2007
Posts: 17

I have no idea your knowledge on late model cars and GM's stuff and you sound pretty smart but I will for now assume ignorance. The Dexcrap you have in that Sonoma is the worst coolant on the face of the planet and it will eat through heater cores, water pumps, radiators, and so on. GM knows it and they are too pigheaded to make a change. Furthermore, they have a general bulletin on all vehicles i.e. all brands under the corp. (I think) that use Dexcrap that if you are having problems -- leaking, overheating, R/R parts, etc. to drain, flush w/ water, flush w/ Prestone Flush, and then the ****ty part refill with Dexcrap. Scrap the last part and refill with your favorite green stuff. Hint-Evans Coolant. They have a whole lot of stuff on their website about Dexcrap. However if you want to keep the Dexcrap in your vehicle then GM does sell their sealant tabs "to renew" the antifreeze.

Have fun!
Old 11-16-07, 12:55 PM
Join Date: Nov 2007
Posts: 1
A very similar issue

All this is very interesting and I have a very similar issue.

My truck seems to run in the normal heat range and for no apparent reason the heat, for most part, stops. I thought the heater core was blocked, flushed it with water and saw no evidence of a blockage. Just clear water came out. .(There as coolant at first) The floors boards are dry and there is no sweet smell of coolant. After flushing, the heater seemed to work fine for a while then the same symptoms reappeared.

I was told by the GMC dealer that my water pump was going (leaking from the weep hole). I replaced the water pump and hoped this would also fix the issue of no heat. It did, for a while and no we are back to cold mornings.

I have noticed that when ever I R/R the radiator cap the heat works well, for a while.
All this leads me to believe there’s an air pocket some where in the cooling system.

Kind of like a reverse vapor lock.. Or am I dating myself?

Any ideas?


Old 11-16-07, 04:53 PM
Join Date: Nov 2007
Posts: 17

R/R List-->

water pump


Good luck
Old 11-16-07, 05:11 PM
Banned. Rule And/Or Policy Violation
Join Date: May 2007
Location: Wisconsin
Posts: 8,629
In the very beginning of such a diagnosis, it is imperative that the cooling system is full of coolant, no air is in it, and after driving it to get the thermostat to open and close and circulate coolant, you check to see if you have to add more. And do so if need be.

Then make sure you know exactly where the coolant level is in the reservoir cold. And make sure the radiator is topped off.

Then drive the car. After it has cooled back down, the coolant should be right up to the bottom of the cap. And the coolant level in the reservoir should be where it was the last time the engine was cool. If it isn't, obviously you will want to add more and drive it again, to see what is going on - if you have an air pocket you never got rid of or if you have a more sinister problem. You can't have air pockets and expect water to circulate properly through the cooling system and heater hoses, with normalcy and consistency.

If you are never ever able to get to the point where you can have the car cool down, and then open the cap and find coolant right at the bottom of the radiator cap, you have either an external leak or something going on that is sucking coolant into your engine and burning it. Or,if you find that water is down in the radiator but mysteriously rose to a higher level in the reservoir.

If you have such an issue, this reeks havoc with the heating system and the gauges and everything will act berserk and sporadic; alternating hot and cool. The radiator fan may or may not come on if coolant is below the sensor by your thermostat. You can be fooled itno thinking your fan relay has gone out on you. That is why the coolant level monitoring is imperative.

Make sure your cap is good and maintaining pressure, and that passageways in the cap are free to allow passage of coolant between reservoir and radiator, and that no hoses are loose, or thermostat housing is loose, or water pump is weeping, or that the lower radiator hose is not collapsing. Make sure not one drop of coolant winds up on a clean parking pad.

Bottom line is you can speculate on many things, but until you confirm what your coolant level is doing from day to day and where it is in the radiator when you get ready to start your cold car, you'll just be guessing. Personal experience(s) is talking here.
Old 11-19-07, 07:18 AM
Thread Starter
Join Date: Jan 2007
Posts: 58
Sonoma Cooling and leaks

I know I have a leak. I can see the coolant leaking out of the fitting onto the manifold and down the front of the block (if that it is what its now called... the thing onto which the carburator used to go. I guess now its just the air intake)

Anyway, there is a tube, about 1 1/4 inch diameter with a welded 2 bolt flange that bolts onto the manifold that connects to the radiator hose. Thats where my leak is: at the flange/manifold connection

Looking at Rock Auto parts I think there is a buck and a half O ring as the seal. Otherwise from the outside it does not look like there is a gasket on that connection.

Anyone know for sure if there is an O ring ? Or what is supposed to seal that connection ?
Old 11-20-07, 08:30 AM
Thread Starter
Join Date: Jan 2007
Posts: 58
Sonoma cooling issue/leak

I went to a local auto parts store yesterday and bought what they told me is the part to seal my leak. For a buck and a half I got what I would describe as a square cross section o-ring about 1 /1/2" diamter. It looks like what the part ought to be.

So, if the snow stops, I will get at it in the next couple of days.
Old 01-29-08, 05:20 PM
Thread Starter
Join Date: Jan 2007
Posts: 58
Sonoma Heating (and Cooling)

I'm back. I have yet to get to the o-ring seal but my truck appears to have 'mostly' self healed its leak. I can tell the leak is at the intake inlet and if it ever warms up here in Mass. I will swap it out. But, I have had to add only, may-be, a cup or two of antifreeze.

HOWEVER: this week's problem is frost bitten feet. A repeat problem I am afraid that is a 2 or 3 year old issue. The heating system works great but the diverter in the duct work I am pretty sure, is again, broken.

A few years ago the same issue occurred but the truck was under warranty and the 'know-it-all' service manager quickly diagnosed the problem (after I told him what it was) as the diverter in the heater duct was broken. I had wiggled my way under the dash and essentially found all the vacuum lines working great but the extended 'axle' from the diverter inside the duct work, to the connection on the outside, broken where is goes into the duct.

This is a cheap plastic piece of crap, flimsy hardly describes it. I am thinking that perhaps a bit of moisture freezes the door in some position, then, you actuate it, and snap ! The weak link gives.

Anyway, here is my question. Does anyone know about disassembling this mess ? It sure seems like a lot of work which is not that bothersome but I am wondering if there are any tricks or knacks ? Moreover, I do not want to replace the crappy part. At the very least I am wondering if General Motors has done a change to improve it....sorry, but I had to inject some humor, or I guess I will find a way to 'bullet proof' it when I take it apart. Too much work to screw with this again.

When it was repaired under warranty, the dealer charged GM over $400 with labor and a few bucks worth of parts.

I am convinced this issue is the diverter in the duct. Everything else with the heater works fine but when you switch to foot postion, you get nothing except for a roar inside the dash like something that ought to be open is not.

Last question: are there ways to determine if there might have been some sort of recall, refit, or whatever for this crappy General Motors design.. (Again, sorry for the laugh, but I had to ask)

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