Eric (72.56.7.192) - Fri Dec 5 00:17:50 2008

My 1999 chevy venture van''s heater only blows hot air at highway speeds. When we stop or slow down, it only blows cold air. About the time this started, I noticed that the temp gauge bouncing around alot. Gauge is at normal levels on the highway, but goes very hot, then cold when slowing down and stopping. Bad water pump/thermostat? Coolant levels is good. Any ideas?

thanks!

Eric

Reply #1 Tony (99.230.154.42) - Mon Dec 22 23:06:43 2008

I have the same problem

when you find out the cause please let me know

Reply #2 kerfy (24.89.67.174) - Fri Jan 9 10:49:44 2009

same thing with mine at idle the temp gage goes way up then when i rev it up the heat comes back and the temp goes down

when i try for real high revs it surges ???

related??

Reply #3 Chris (209.192.1.102) - Sat Jan 10 13:19:19 2009

I have the same fluctuation in my temp hand. I started by replacing the water pump, thermostat, temp sending unit, and radiator cap, but those did not solve the problem. I recently put on a new set of intake gaskets for the both upper and lower (5hr job), but that has not solved the problem either. Now I suspect an air bubble in the cooling system after all that, but no matter how much air I bleed from the system I continue to get the fluctuation. Did any of you solve the problem yet?

Reply #4 kevin (96.225.86.143) - Fri Jan 16 12:09:43 2009

i have the same problem ....cannot resolve....please someone help!

Reply #5 Michael Gray (75.186.90.208) - Fri Jan 16 20:20:02 2009

Try replacing the Serpentine belt, sounds like it might be slipping.

Reply #6 Tressel (99.234.112.127) - Sun Jan 18 10:53:37 2009

My 2001 Venture Cabin Heater was week and finally it totally gave up. I have Flushed the cooling system and replaced the Thermostat 3 months ago. Engine temp is steady @ 85 deg. Line goes to Heater is nice and hot comming out of core is cold.

Before I replace the costly heater core I would like to check the pipe piece attached to the head with a priming screw on top. This should be doing the all important coolant flow in and out of the heater core. When take a sharp left turn while driving I get a short blow of nice hot air for for few seconds. could that mean the heater core is not blocked?

Please help me at your earliest as i have to drive in very cold winter in Toronto.

Reply #7 Jim (72.140.218.235) - Mon Jan 19 09:03:07 2009

I own a Venture 2000 and had the following symptoms: Cabin heater would blow cold unless I turned a sharp corner or revved the engine or ran at highway speeds. Occasionally a rapidly fluctuating temperature gage, but not always. Bubbles coming into the coolant over flow tank, frequent, but not all the time. Smell of combustion gases in the coolant over flow tank. Occasionally the "Low Coolant" warning light would come on. Gurgling sound coming from the dash, frequently. (Needed to have the blower turned to low or off to hear it.)

After a great deal of investigating and reading and talking with mechanics (and I am a relatively ok backyard mechanic myself) I concluded that I had a bad head gasket. (This is a relatively common problem with these 3.4 l engines. Poorly designed intake manifold gaskets and problematic Dexcool coolant initiate a coolant problem which, if not properly dealt with, can cause the engine to overheat, warping the head(s) and causing a bad head gasket.)

I tried two different types of coolant additives to try and seal the problem. (Moroso and Thermagasket) without success. I am not saying they don't work, they just didn't work in my case.

Facing a potential $2400.00 repair, I decided to replace the head gaskets myself. (I'm fortunate to have family that own a heated garage.) There's a good reason that this job costs $2400.00 to do. It is a huge undertaking. Sure enough, both headgaskets were bad, and in fact the heads were so severely pitted next to the area where the gaskets were bad that I needed to replace the heads as well. My costs, about $1200.00, and about 30-40 hours of my time. I now have a well running van, with all previous symptoms addressed except one, the lack of heat. I now need to replace the heater core (12 hour job, $200.00)because the coolant additives I used to try and fix the head gasket leak prior to my head gasket repair have plugged my heater core to the degree that it only provides low grade heat.

I will NEVER buy another GM... EVER...Ever...ever...

Jim

Reply #8 Tressel (99.234.112.127) - Wed Jan 21 21:03:41 2009

Jim

Thanks for your input. Everyting you mentioned made perfect sence to me. I have the identical cabin heating problem. I took to a garage and got it cleaned and paid $ 250 and it worked only for just 2 days. Now I know as a fact that it is nothing but the heater core instead of paying another $ 700. I am a boat tech and got a fair idea. I am going to buy a Heater Core and install it myself. Last summer I removed everything from inside and got stuck as I could not remove the QUICK COUPLINGS ATTACHED TO IN/OUT HOSES BETWEEN THE ENGINE AND CORE. Can you please findout the way to remove those couplers. I am planing to go for it this weekend.

Reply #9 jim (71.110.246.172) - Thu Jan 22 17:54:37 2009

I HAD THE HEATER , AND THE GAUGE PROBLEM . THE SYSTEM HAS AN AIR POCKET. I HAD TO KEEP RUNNING THE ENGINE TO HALF WAY ON GAUGE. THAN WAIT FOR IT TO COOL OFF 3 TO 4 TIMES AND KEEP ADDING COOLANT TO THE RADIATOR EVERY TIME IT COOLED OFF TILL I GOT ALL THE AIR OUT.

Reply #10 Tressel (99.234.112.127) - Thu Jan 22 21:11:20 2009

I have no cooling water priming problem. My water level and gauge is steady at just a scale before halfway when running.

My big Question is the way to remove Heater Core in/out Water connections attached from engine. They are not hose clamps but special quick couplers. Wonder whether I need a special tool for that?

Thanks

Reply #11 Truman (99.16.131.203) - Sat Mar 28 13:18:45 2009

I have an 01 Venture that I just got (great purchase...chuckle chuckle). So, I have similar problems with the temperature bouncing all over without heat and on other days it works. So, I was going to "burp" the engine this weekend to see if that would help and now I find that the coolant leaks out almost as fast as I put it in. I am not sure where, but it is leaking out underneath from around the transmission pan. Any ideas? I am thinking head gasket...yikes. Any help would be appreciated as I am not all that mechanical...Should I try a sealant?

Reply #12 01 venturer (24.146.15.11) - Sun Apr 5 13:12:08 2009

Try checking your sensors i have same problem and i think there are 2 sensors that control the fans and another get those checked.

Reply #13 John (69.246.116.30) - Thu Apr 16 00:13:27 2009

I have had the same problem with my 2000 Venture aswell as a 2001 Caviler and 2000 S-10. On all 3 of the GM vehicles it was a highly restricted or clogged heater core each time. From what I was able to find out is that you must drain and replace the Dexcool every couple of years our it has a tendency to turn into a jello like substance in the heater core (don't know why). I have switched my GM cars all over to Prestone 50/50 because the Dexcool seems to be so problematic and having to backflush a heater core every couple of years is a pain.

Reply #14 SkiMask (4.53.82.70) - Sun Jun 28 12:55:40 2009

The fluctuating temperature gauge definitely denotes head gasket problem. Had mine replaced last year. Runs great since. The Dexcool coolnat rots out engines.

Reply #15 bill (72.209.159.165) - Tue Oct 13 18:17:59 2009

have a 2000 chevy venture, it is blowing cold air instead of blowing hot air when the heater is on, changed the thermostat and it didn't make a difference, i am assuming it is the heater core and wondered can it be flushed out without taking it out of the van? any help would be appreciated, thanks

Reply #16 Jim (97.125.109.80) - Wed Oct 14 01:13:37 2009

You all have experienced the same things. The coolants system is one of the most common thing that gets neglected on a motor vehicle. If they are not back flushed on a regular schedule the system will slowly plug itself. By not draining the coolant every year and replacing with fresh water and anti-freeze the improperly mixed anti-freeze and water will cause the system to rust from the inside out. The debris will trap inside the heater core as it contains the smallest chamber in order for it to produce a steady flow of hot air while a fan blows on it regardless of RPMs. Your heater cores are on the way to being fully plugged. Parts stores have a back flow flush kit for around 6.00 which will allow you to flush the sytem yourself. The trick is to isolate the core itself and flush it out seperately once the rest of the sytem has been flushed. This is done by pinching off the inlet before the flush valve and only running water through the core. If it does not flow freely at low pressure then it will need to be replaced. Newer vehicles regardless of brand are all difficult to replace a heater and in most cases require pulling the entire dash out. This is why the repairs bills are so high. Most cores are less than a hundred dollars unless your vehicle has two cores.

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