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Car Forum / Driving, Maintenance, Tuning / Maintenance and Repair / February 2006No Heat Unless At Highway Speeds
Assuming the coolant level is fine, what would cause the heater to only put out hot air at highway speeds? This is a 1990 3.1 L Chevy with 200 + thousand miles on it. I replaced the heater core 9 months ago, the radiator was done this week by a shop. When I got the car back from the shop, it no longer put out heat unless you were on the highway. Obviously the shop will have to correct this, since it wasn't a problem when the car went in, but I'm wondering what could have happened? >Assuming the coolant level is fine, what would cause the heater to only >put out hot air at highway speeds? This is a 1990 3.1 L Chevy with 200 [quoted text clipped - 5 lines] >to correct this, since it wasn't a problem when the car went in, but >I'm wondering what could have happened? suspect a worn impeller in the water pump. I've seen how they can all but disappear from electrolysis between the coolant and the metal. If this is the case, you should get the same heat when you take up the rpm's to highway level. IOW 2,300 rpm IN NEUTRAL WITH THE EMERGENCY BRAKE ON...if you get heat, it's the water pump. If that doesn't happen, it is something else. Blower motor working OK? >Assuming the coolant level is fine, what would cause the heater to only >put out hot air at highway speeds? This is a 1990 3.1 L Chevy with 200 [quoted text clipped - 5 lines] >to correct this, since it wasn't a problem when the car went in, but >I'm wondering what could have happened? Most likely, when they replaced the radiator they did a POWER FLUSH and sent all the debris inside the cooling system into the heater core, clogging it up. > Assuming the coolant level is fine, what would cause the heater to only > put out hot air at highway speeds? This is a 1990 3.1 L Chevy with 200 [quoted text clipped - 5 lines] > to correct this, since it wasn't a problem when the car went in, but > I'm wondering what could have happened? Did they forget to put the thermostat back in? What's the gauge reading? And if it blows good heat on the highway, what happens if you stop - does it go away or is it ok and just takes really long to warm up? Ray That can easily be caused by an air bubble in the heater line. On some, the heater hoses can physically sit close to the top of the coolant level in the rad or even up a bit higher. This can lead to an air lock in the line that required the faster pump speed to get some fluid past it. Mike 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's Canadian Off Road Trips Photos: Non members can still view! Jan/06 http://www.imagestation.com/album/pictures.html?id=2115147590 (More Off Road album links at bottom of the view page) > Assuming the coolant level is fine, what would cause the heater to only > put out hot air at highway speeds? This is a 1990 3.1 L Chevy with 200 [quoted text clipped - 5 lines] > to correct this, since it wasn't a problem when the car went in, but > I'm wondering what could have happened? Air probably is in the system. I hear a gurgling sound coming from the heater core when I start the car in the morning. I had tried bleeding the air out multiple times, but no luck. I figured that the air was getting in to the system due to the leaking radiator and thought replacing the radiator would solve the air in the system problem. After the work was completed, the radiator shop said that I would still hear the gurgling sound because the flow rate of the coolant entering the heater core is too high. The explanation I was given is that the hose that feeds the heater core connects to a metal pipe. The metal pipe has a reducer that slows the flow of coolant into the heater core. The gurgling was due to the fact that the reducer had eroded over the years, and was no longer slowing the flow of coolant into the heater core. I've never seen nor heard of such a part on this particular engine, so I either think this person was misinformed, or only interested in the radiator replacement and not really in solving all the problems. I'm going to bleed the system again. If the gurgling sound persists, what next? Another pressure test for leaks? Ideas anyone? >Air probably is in the system. > [quoted text clipped - 18 lines] >I'm going to bleed the system again. If the gurgling sound persists, >what next? Another pressure test for leaks? Ideas anyone? I have never heard of what I am about to suggest being done. Therefore, it is most likely not a good idea. To other people. You want to take air out of your upper radiator hose? Start the engine so the water pump is running and attempting to circulate water. Inject a SYRINGE into the highest point of the upper radiator hose and withdraw trapped air ( where else would it be ? ). You can only penetrate the wall thickness of the hose. If you go deeper, you are likely to leave air in the top of the hose. When you withdraw they syringe, after purging the air in this way, the hose should self-seal. If it doesn't, use a small plug with rubber cement. I say this is OKAY because there is only 16 PSI in my cooling system. That is 2 PSI over atmospheric pressure. Almost nothing. If the hose doesn't *self-seal* then you can tape it, but I highly doubt 2 psi is going to force hot coolant out of the pinhole. Lg > >Air probably is in the system. > > [quoted text clipped - 39 lines] > > Lg I'm going to guess this is a bad idea, but only because I think you are making an incorrect assumption. the 16 PSI is not absolute, it is referenced to atmospheric pressure. nate > >Air probably is in the system. > > [quoted text clipped - 39 lines] > > Lg Ya gotta be kidding right? They are multi layer hoses and they sure as hell don't self seal nor does cement repair them. A rad cap blows when it sees 16 psi 'difference' also. Mike 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's Canadian Off Road Trips Photos: Non members can still view! Jan/06 http://www.imagestation.com/album/pictures.html?id=2115147590 (More Off Road album links at bottom of the view page) > I have never heard of what I am about to suggest being done. > Therefore, it is most likely not a good idea. To other people. [quoted text clipped - 5 lines] > penetrate the wall thickness of the hose. If you go deeper, you are > likely to leave air in the top of the hose. This is a really bad idea. > When you withdraw they syringe, after purging the air in this way, the > hose should self-seal. If it doesn't, use a small plug with rubber > cement. It won't self seal and here is no plug or rubber cement that is going to hold. > I say this is OKAY because there is only 16 PSI in my cooling system. > That is 2 PSI over atmospheric pressure. Almost nothing. If the hose > doesn't *self-seal* then you can tape it, but I highly doubt 2 psi is > going to force hot coolant out of the pinhole. Cooling system pressure is 16 PSI -above- atmospheric, IOWs, 30 PSI absolute. Best way to re-fill a cooling system is with an air lift. >> I have never heard of what I am about to suggest being done. >> Therefore, it is most likely not a good idea. To other people. [quoted text clipped - 24 lines] > >Best way to re-fill a cooling system is with an air lift. Okay okay. Dumb idea. Sometime this coming spring/summer I am going to have to flush my own cooling system. That should be a *hoot* as I can't get at anything except the radiator drain petcock. Right now, my *adventure for the time being* is making certain my alternator is putting out juice ALL the time the engine is on ( SO FAR SO GOOD!) I think a combination of *things* fixed that. First the funky plug at the voltage regulator, then the New serpentine belt. I've seen nothing but *good* results since _both_. Just the VR plug was a partial fix. Then the new belt =seems= to have taken care of the rest. In retrospect, that old belt _did_ look like crap! Now IF I am *out of the woods* with that problem, I can move on to the new coolant. That's a big IF. So far, I am getting continuous and immediate alternator output. That is a sign, but until I put more trips and miles on the car, I'm not going to give it two thumbs up. Call me paranoid. And the other thing is, alternators cost a _bunch_ of money. I would have to take it back to the dealership for warranty repair, if I even still HAVE a warranty for that in effect. The deal was 36,000 miles or 36 months, whichever came first, and the 36 months were not from when I bought the car, but from when the car first went into *service* as a dealer demo. So...I might be avoiding a costly repair bill by avoiding the dealer shop at the moment. I think my *warranty* has most likely expired by now ( 36 months-wise ). I have before me, what is called a Victor brand Universal Cooling System Flush Kit. ( for *most* cars ). I just don't want to mess with it at the moment because it is friggin freezing here at the moment. Spring/summer sounds like a better time to get in there for cooling system service. So...you can do this. Find out Inner Diameter of Upper Radiator Hose. Go buy some PVC pipe with a screw-on T fitting ( this exists, as I installed SAME when I re-plumbed my bathtub drain ). Cut the top rad hose at its' highest spot, insert fitting with screw-on T-drain. Hose clamp the thing in place. In fact, I might do this myself, guessing at the inside diameter of the radiator hose after measuring somewhere I can, like the thermostat fitting. Lg Thanks for the ideas. I'm thinking trying Mikes suggestion of raising the nose of the car. This car does have a bolt on the thermostat housing for bleeding. I'm thinking replacing the bolt with a valve to make it easier to bleed the air. Below are the steps for refilling the cooling system - condensed them from the factory manual. I always added coolant to the radiator with the engine running, but that is not listed in this procedure. Would running the engine with the radiator cap in order to add coolant introduce air into the system? 1. Slowly fill the cooling system through the radiator neck until the level of the coolant mixture has reached the base of the radiator neck. Wait two minutes and recheck the level, adding more coolant mixture if necessary to restore the coolant mixture level to the base of the radiator neck. 2. Install radiator cap. 3. Close all air bleeds. 4. Fill the coolant reservoir with coolant mixture. > Thanks for the ideas. I'm thinking trying Mikes suggestion of raising > the nose of the car. This car does have a bolt on the thermostat [quoted text clipped - 18 lines] > > 4. Fill the coolant reservoir with coolant mixture. Is the thermostat housing on the top of the engine? If so it might be a good idea to fill there first then install housing and top off the rest of it. Then if the "bolt" is really a pipe plug, you can replace it with a petcock (like you have in the bottom of your radiator) so you don't need any tools to bleed it farther. good luck nate I have been bitten by this before, if you have a coolant pump with high miles it probably is that. take some clear rubber hose install it on your heater core inlet, or splice it between the inlet hose. by doing this you can see if you have flow. if you don't have flow when up to operating condition, heater on, then check and see if you have a heater control valve. sometimes they have plastic valves in them that don't open far enough or even break off. the first guy is right about the fins on the pump erroding away due to electrolesis, you see this more often in foreign cars with plastic fins that break off. hope you find the problem, just keep chippin away and try the easy fix first. I know you would think that you would over heat with broken or eroded fins but thats not the case.  Signaturesavannah75 http://www.automotiveforums.com > Find out Inner Diameter of Upper Radiator Hose. Go buy some PVC pipe > with a screw-on T fitting ( this exists, as I installed SAME when I [quoted text clipped - 5 lines] > > Lg Are you contemplating leaving the PVC fitting in there permanently? >> Find out Inner Diameter of Upper Radiator Hose. Go buy some PVC pipe >> with a screw-on T fitting ( this exists, as I installed SAME when I [quoted text clipped - 8 lines] >Are you contemplating leaving the PVC fitting in there >permanently? Yes, I don't see why not? It isn't like it is going to be burned through or melted by the exhaust manifold. If that were the case, the heater hose itself would be fubar by now. What is the problem with that? The overflow tank is PLASTIC! it gets hot coolant all the time. It is so cheesy I can almost poke a hole in it with my finger. The overflow bottle pressure cap looks like it came off a 2 liter soda bottle. Do you really think schedule 40 can't handle the engine compartment environment? > >> Find out Inner Diameter of Upper Radiator Hose. Go buy some PVC pipe > >> with a screw-on T fitting ( this exists, as I installed SAME when I [quoted text clipped - 18 lines] > came off a 2 liter soda bottle. Do you really think schedule 40 can't > handle the engine compartment environment? Maximum surface temperature of schedule 40 PVC = 140* F <http://www.harvel.com/pipepvc-sch40-80-derating.asp> Your top radiator hose where you intend on installing this may see 240*F or higher. Underhood temperatures in the summer, that or higher... Also, two more hose clamped connections = two more places for leaks to develop. >> >> Find out Inner Diameter of Upper Radiator Hose. Go buy some PVC pipe >> >> with a screw-on T fitting ( this exists, as I installed SAME when I [quoted text clipped - 28 lines] >Also, two more hose clamped connections = two more places for >leaks to develop. OK. Won't do it then. You've saved my bacon once again. One day, I am going to send you a BLT sandwich. Lg >>Find out Inner Diameter of Upper Radiator Hose. Go buy some PVC pipe >>with a screw-on T fitting ( this exists, as I installed SAME when I [quoted text clipped - 8 lines] > Are you contemplating leaving the PVC fitting in there > permanently? Can I hijack this thread? On my enduro dirt Camaro, I was thinking of a second rad in the backseat area or something for extra cooling - 200 laps on dirt = nose full of mud and slowly rising temps (or quickly rising sometimes) but don't like the idea of 10 foot runs of heater hose... plus it's not that cheap when you need 20+ feet of it. I was thinking 1.5-2" exhaust pipe... I know it'll eventually rust, but this is a race car that sees fresh water on a regular basis. Hell, it sees new engines on a regular basis because I keep finding new ways to blow them up. Any thoughts on this? It's not just my car that overheats, I'd say about 50% of the cars are overheating in the average race. 2 hours of full throttle = way more heat than a stock size radiator can dissipate - I have a big rad (and it's new) in there and a flowkooler water pump, but we all run hot by the end... Ray >>Air probably is in the system. >> [quoted text clipped - 39 lines] > >Lg No, it's 16 psi OVER atmospheric. It's a differential measurement, not an absolute one. >>>Air probably is in the system. >>> [quoted text clipped - 42 lines] >No, it's 16 psi OVER atmospheric. >It's a differential measurement, not an absolute one. Okay. So...that still isn't a whole lot. It is a far cry from hydraulic pressures which are thousands of pounds per square inch. 16 psi Over 1 atmosphere can be *handled* by PVC. I might do this *mod* myself now that my car is going out of warranty, but not until the weather warms up a lot. Sometime in the late springtime would be a good time to service the cooling system, or even early summer. Once winter moves in up North here, it is minimal necessary maintenance and emergency repairs only unless you have a heated shop with a lot of space and good lighting ( and heating ). My plan is to find the block drain plugs and open them. Flush the radiator as 1 unit flush the engine block as 1 unit flush the heater core as 1 unit Fun in the sun. Right now, it is dark and cold. Car seems to be solid enough, so I'll keep my fingers crossed I make it to Spring/summer with no more problems. Lg > I'm going to bleed the system again. If the gurgling sound persists, > what next? Another pressure test for leaks? Ideas anyone? I'm pretty sure your car doesn't have any special procedures for bleeding the system, but it might - my Firebird does and my Fiero did. When in doubt, the rad cap has to be the highest point in the system to get all the air out. Maybe jacking the front end up would help with it running? On cars that I've had air in the system, I've been usually able to get rid of it just by filling up and topping up for a couple of warmup cycles to get all the air out. I dunno about the gurgling sound - it may be a red herring on your quest for heat. > Air probably is in the system. > [quoted text clipped - 18 lines] > I'm going to bleed the system again. If the gurgling sound persists, > what next? Another pressure test for leaks? Ideas anyone? There is most likely air in the system. I would strongly recommend that you take the car back to them to have the air bled out. Most manufacturer shop manuals have a specific procedure outlined for this and it will differ between cars in my experience. To help the radiator shop complete the job you might want to ask the service department at the dealership for the steps needed to effect a full purge of air. > There is most likely air in the system. I would strongly recommend > that you take the car back to them to have the air bled out. Most > manufacturer shop manuals have a specific procedure outlined for this > and it will differ between cars in my experience. A "good" shop will have a device that hooks to your radiator cap and puts a vacuum on the system to purge out the air. Not all shops have this tool, but a lot of todays cars almost have to have it done to get the air out. Of course, the cooling system gaskets need to be in good shape. I'm always leary about using this on an a GM 3.1 or 3.4........ I would first eyeball the hoses to make sure one isn't running up too high. I have had to re-route 3 of my vehicle's heater hoses because someone ran them wrong or ran flex hoses when molded was called for so they were too high. I then would park the vehicle with the nose way up in the air if possible and warm it up with the rad cap off while topping up the fluid. You might have to do this a few times. Some engines have a bolt on the head or thermostat housing to bleed them, but I don't think yours does. I have seen folks put the flush kits on the top heater hose so they can open up that cap to let air out on stubborn ones rather than buy the molded hose. Mike 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's Canadian Off Road Trips Photos: Non members can still view! Jan/06 http://www.imagestation.com/album/pictures.html?id=2115147590 (More Off Road album links at bottom of the view page) > Air probably is in the system. > [quoted text clipped - 18 lines] > I'm going to bleed the system again. If the gurgling sound persists, > what next? Another pressure test for leaks? Ideas anyone? I'm sorry, I have changed dozens of pumps and rads on these. It might not be easy, but with the engine running and warm, wrap your hand arouond the heater core hoses and feel the heat. Don't be afraid to lay right across the motor with your chest on the plenum. If one of the hoses are at a completely different temp, you have a circulation problem. If the problem started after the rad was done, the mech did not "burp" the system and the coolant is low. If the rad was changed because of the heat problem, it was mis diagnosed. If you think it is a clogged heater core, back-flush the heater core only. In the 21 years I have been doing this I have never seen long term air traps. Engines are "burped" and purged of air within a short period of time. At highway speeds and thermostat open all air will purge. The only way there can be air trapped is if there is no activity in the system. So, the only way you can trap air in the system for a week is to not run the engine. Also, all heater cores are lower then the rad cap. If this was not so, every time you opened the cap coolant would come out. If circulation is not the problem chack the hot/cold door in the mode valve. Got news for ya! The last 2 vehicles I have purchased as well as a few in the past like my Chevy pickups have had replacement heater hoses put on them. These hoses were bulk flexible hoses rather than the factory molded hoses. This meant that the physical run of the hose wasn't stock and some part of the hose ended up higher than the top of the coolant in the rad. This made for really crappy heat. They would only blow luke warm unless the rpm were really high. I rerouted most of them to be down, but one on my Cherokee wouldn't go lower. Turns out the coolant level in the closed system's reservoir just needed to be 1" higher to get above the heat hose and now we have good heat. My CJ's has a loop over the valve cover, so I need to put it nose up to get that air out.... I guess if you work in on new vehicles, you would only have seen newer hoses in the last 21 years..... Mike 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's Canadian Off Road Trips Photos: Non members can still view! Jan/06 http://www.imagestation.com/album/pictures.html?id=2115147590 (More Off Road album links at bottom of the view page) > I'm sorry, I have changed dozens of pumps and rads on these. It might > not be easy, but with the engine running and warm, wrap your hand [quoted text clipped - 17 lines] > If circulation is not the problem chack the hot/cold door in the mode > valve. I think paulv is may have the answer I checked again yesterday morning with the engine cold. The overflow bottle was at the "full cold" mark, but the radiator was down a couple of inches from the filler neck. I added coolant to bring the coolant level up so that it was even with the bottom of the filer neck. Checked again this morning, and the coolant level in the radiator is good. How long do you have to drive at highway speeds in order to get the air out of the system? Also, the only thing you should poke your hoses with is a cotton ball. |
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