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Car Forum / Driving, Maintenance, Tuning / RVs / February 2007Chevy 454 that only provides heat when idling 1996 Allegro
I'm running out of ideas - help We get between 80 - 148 degrees from heat vent when idling then drops to 70 degrees when driven a few miles or with engine rev'd for a few minutes. * Ambient temp was 45 deg * 6 years and 25,000 miles since we noticed the problem * Engine has never overheated and the temp gage runs consistently around 210 * The engine runs like a champ - Just no heat What's been done: * Air lock - Checked and clearer lines * Thermostat - Checked/replaced * Radiator cap - checked/replaced * Vacuum pressure - checked * Heater control valve - checked/replaced * Coolant line routing checked * supply from the back of the block - goes to the bottom connection of heater core * return from top connection of the heater core to top of radiator * Coolant supply lines - replaced * Pentium and heater core box seals - checked * Blend air door - checked * Heater core - replaced * Installed clear tube in heater supply line -small bubbles at idle - turns to foam at higher RPMs * CO2 coolant/block tested - indicated low level of CO2 in coolant * Heads - magnafluxed - No cracks, minor warping - planed heads and replaced * Water pump - replaced when heads done * Radiator hose - replaced * Power flushed system and block * Pressure tested system What in the world could this be? * small hole in the block? * still a crack in one of the heads? -------------------------------------------------------------------------------- 1996 Allegro RV with 1996 Chevy 454 block casing number 10237297...454.......96-up...4-bolt, Vortec 7400", "L-29" Gen.VI I see where abelings@aol.com contributed: >I'm running out of ideas - help >We get between 80 - 148 degrees from heat vent when idling then drops >to 70 degrees when driven a few miles or with engine rev'd for a few >minutes. ............... >What's been done: >* Air lock - Checked and clearer lines [quoted text clipped - 23 lines] >* small hole in the block? >* still a crack in one of the heads? Impossible to diagnose correctly from a distance, but one thing is certain: bubbles and foam suggest cavitation at the water pump. I'm guessing it is not a cracked block/head, else it would overpressure the system and blow out coolant under load. Are you sure hoses are routed correctly? I seem to recall OEM routing different than you describe. Will Sill The Curmudgeon of Sill Hill >Impossible to diagnose correctly from a distance, but one thing is >certain: bubbles and foam suggest cavitation at the water pump. I'm >guessing it is not a cracked block/head, else it would overpressure >the system and blow out coolant under load. Are you sure hoses are >routed correctly? I seem to recall OEM routing different than you >describe. This is a tuff one. I still tend to think that it is low on coolant and that it has a air slug in it that was never removed properly. Some BB emgine can be really fussy about this. I would not rule out a leaking head gasket since you did have heads of recently. You might do a compression check of all cylinders to look for signs of leakage. The routing of the coolant for it is correct. If all checks okay, take enginen through a few hot to cold cycles to let it purge into overflow and suck bacl extra coolant when it cools. Make sure overflow is full and check retrun line from it to raditor to make sure it is not sucking air in when it cooling and siphons coolant back. ----------------- TheSnoMan.com In a recent message, Will Sill <will@epix.bnet> opined: >I see where abelings@aol.com contributed: >>I'm running out of ideas - help [quoted text clipped - 39 lines] >Will Sill >The Curmudgeon of Sill Hill True but he mentioned "some" CO2" in the coolant which does indicate a combustion leak somewhere, and that will also cause foaming..... Mark I see where Mark Tetrault <mdtetrault@highstream.net> contributed: Will: >>Impossible to diagnose correctly from a distance, but one thing is >>certain: bubbles and foam suggest cavitation at the water pump. I'm >>guessing it is not a cracked block/head, else it would overpressure >>the system and blow out coolant under load. Are you sure hoses are >>routed correctly? I seem to recall OEM routing different than you >>describe. Mark: >True but he mentioned "some" CO2" in the coolant which does indicate a >combustion leak somewhere, and that will also cause foaming..... I repeat: Impossible to diagnose correctly from a distance. But wouldn't a combustion leak big enough to interfere with heater circulation quickly blow out coolant under load? I admit this is a tough one. Will Sill The Curmudgeon of Sill Hill >I'm running out of ideas - help >We get between 80 - 148 degrees from heat vent when idling then drops [quoted text clipped - 37 lines] >1996 Allegro RV with 1996 Chevy 454 block casing number >10237297...454.......96-up...4-bolt, Vortec 7400", "L-29" Gen.VI Hi, Only thing you haven't mentioned is the fan and clutch both working ok I would presume. :) If you are getting foam into the heater then you are not going to be getting any heat, or at least not much. Are you leaking or using any antifreeze? If you are, finding out where it is going and stopping the leak would probably solve the problem of course. Intake or exhaust manifolds are most likely leaks, along with water pumps and coolant line connections. Normally you would check the input and output lines of the heater to see if they are the same or close to the same temperature when calling for heat. Cooler output could mean a blocked or bad core. Since you are saying you are getting heat at idle the problem is more then likely the foaming of the coolant coming into the heater. You are introducing air into the coolant system when the water pump is turning at above idle speed and supplying more pressure to the system. Foam in coolant can result from trapped air in the system, a leak on the suction side of the water pump or an improperly functioning water pump. Low or no coolant in the coolant recovery tank, or the lack of a coolant recovery system. Foaming may also be caused by a lack of anti-foaming agents in the antifreeze or old antifreeze or the combining of incompatible chemicals in the coolant system. Or a small leak in a gasket... Air may be getting into the system as the engine cools down. Does the coolant recovery system work properly including the proper radiator cap? Coolant in when engine heats up, coolant out when engine cools down but always maintaining the recommended low level. Correct type and amount of antifreeze being used? Water pump working properly and seals ok, not sucking air in? No leaks in intake gaskets? You might want to try putting a slightly larger hose on the intake side of the heater, if possible, to try and get more fluid into the core. While this won't solve the foam problem it might help the heating a little. Hope this helps. Take care and Happy Campin...  SignatureRichA "We Get Too Soon Olde and Too Late Smart" The engine runs like a champ - Just no heat>>> Try a low tech cure..........put a piece of cardboard in front of the radiator. Every time I replace a thermostat, I drill an 1/8" hole in it to allow any air to get out as I refill the radiator. SignatureJerryD(upstateNY) Replying to the questions posted: Replaced fan cluch tried cardboard - just increased engine temp. Heat from vent still drops when driving. Here's the temps during testing: Ambient temp 45 This was after running idle 20minites Supply hose 122, return 115, out the vent 97 - Engine temp 205 Down the road - after 1 mile Supply hose 81, return 81, out the vent 82 - Engine temp 205 Down the road - after 2 miles Supply hose 75, return 75, out the vent 75 - Engine temp 205 Pulled over - stand 2-2 minutes Supply hose 120, return 115, out the vent 102 - Engine temp 210 I wonder if the air conditioner is coming on and cooling the water. Try unplugging the wires on the air conditioner pump and try it. SignatureJerryD(upstateNY) > Replying to the questions posted: > [quoted text clipped - 17 lines] > Pulled over - stand 2-2 minutes > Supply hose 120, return 115, out the vent 102 - Engine temp 210 Sorry normally I don't reply to these messages because I don't know that much but has anyone suggested a possible blocked hose? I just wondered as I read someplace about old hoses seperating and collapsing on the inside and it is not visible when looking at the hose. If I remember they said wait until the water heats up then add the gas and see if the thermostat opens and then does the hot water circulate through the hose. Just my 2 cents and that probably is what it is worth. > Replying to the questions posted: > [quoted text clipped - 17 lines] > Pulled over - stand 2-2 minutes > Supply hose 120, return 115, out the vent 102 - Engine temp 210 I'm not an expert on this - but it appears that you are getting very little water circulation. With an engine temp of 205, I would expect your supply hose to be MUCH warmer - like in the 160 - 180 range. Try looping a hose from the supply fitting on the block to the return fitting on the block (NOT going through the heater core and fittings), make sure all air is bled out, and try the same test. Alan >Replying to the questions posted: > [quoted text clipped - 17 lines] >Pulled over - stand 2-2 minutes >Supply hose 120, return 115, out the vent 102 - Engine temp 210 Hi, Are you sure your engine temperature gage is working properly and that you have the right temperature readings. What your temps are showing is that there is little or no hot water being circulated through the heater. The temps at the inlet do not seem high enough if the engine temp is as high as you say. You should be getting 115 degree or higher temp out of your floor heater vent when the engine is up to temp and the blower at medium. Lower then that you have a problem for sure. Your coolant temperature should be at least 160 degrees. 180 or higher is better. Is the input hose hotter nearer the engine? Make sure there isn't a valve or restrictor in the inlet side that is not opening or is blocked. Some times a restrictor is used. Sometimes there is an AC heater coolant shutoff valve that may not be working properly. If all the above is ok then either air lock/foaming or bad water pump most likely or air getting past an intake gasket possible. Or for some reason the water is bypassing the input hose to the heater when the pump is above idle speed. Something blocking the heater input when the water pump is above idle. When you pull over the water isn't being circulated as fast so there is less air being put into it so there is less foam and more fluid flowing through the heater. Or it is going slow enough so it doesn't bypass the heater inlet if blockage is the problem. It sounds like air is getting into the system and not getting out or that something is blocking the heater inlet when the water pump is above idle. Maybe something floating around in the water passage on the engine where the heater input is located. A pressure reading at the input to the water heater while at idle and again while running would tell you if the water is circulating through the input or not. But you can almost be sure it isn't with such low coolant readings. Is your coolant recovery system working properly? Does it always have coolant in the tank even when cold? Does it fill up as the engine gets hotter? What is going into the tank lots of bubbles or just coolant as the engine heats up. Do you have the right pressure cap on the radiator is it on right? Correct thermostat and is it working properly. Have you ever purged the coolant system to get rid of any air in it? Most newer vehicles have air bleeds. The manufacturer should be able to tell you how to purge the engine. A good garage can do it for you with a coolant changer that also purges the air as it changes the fluid. I can't believe you cannot find a garage capable of troubleshooting and solving the problem. Water circulating in an engine is not rocket science. It is either pushed by the water pump or blocked by an air pocket or some type of stoppage somewhere in the system. Take care and Happy Campin... SignatureRichA "We Get Too Soon Olde and Too Late Smart" I appreciate all the great advise and I agree - a good shop should be able to resolve. However, I taken to 6 different shops over the years and each shop thinks they fixed it because they eventually get 100+ deg from the vents when in the shop.. But never fails - when I take it home - cold as ice.. Very frustrating and expensive. There's temperature probes on both sides of the engine that have been disconnected.. The probe on the drivers side has been replaced with an aftermarket probe and gauge. The temps provided during the test are from wireless probes ducktaped to the hoses so they are only represent the temp of the hoses. Best I could do with what I had. The input hose is not hotter near the engine. A A/C heater coolant shutoff valve was mention. It's been replaced - also removed during one of the tests - still no change. There's definitely an airlock/foaming causing the problem. I've been watching the recovery tank. No real changes when doing a heatup/cool off cycle - about 1". The heater core is about 14" above the radiator. So I'm thinking - I"m going to put her on a really steep hill, with the r-cap off see if I can get her to burp. I'm also going to see if I can rig up a bleeder valve on the top heater core line to see if I can get all the air out. >I appreciate all the great advise and I agree - a good shop should be >able to resolve. However, I taken to 6 different shops over the years [quoted text clipped - 21 lines] >can rig up a bleeder valve on the top heater core line to see if I can >get all the air out. Hi, One hundred degrees temps from the vents is marginal at best. When it's on the lower level foot vents you should get at least 115 degrees with the blower on medium. Even that is on the low side 125 to 130 would be better. It would be nice to get a liquid temp reading on the input and output side. You need at least 160 - 180 degrees on the input. One thing is the water pump turning the right way? The belt not on backwards. Don't know if you can do that with the 454 but it can and has been done with other vehicles. Parking on a steep hill and seeing if it will let air out should help. A tee in the highest point of the coolant line with a bleeder on the end might work too. There is sometimes a bleeder screw near the thermostat housing, don't know about the 454. Usually just a hex head screw. Another trick that works on some vehicles to bleed the system is to hold open the negative pressure seal on the radiator cap by inserting half of a paper clip under the seal to keep it open. Put the paper clip in then put the radiator cap back on tight and run the engine. This allows any air to bleed back into the overflow. You need to get hot water into the heater for sure for it to work, foam and air are not good. :) Take care and Happy Campin... SignatureRichA "We Get Too Soon Olde and Too Late Smart" >I appreciate all the great advise and I agree - a good shop should be > able to resolve. However, I taken to 6 different shops over the years [quoted text clipped - 21 lines] > can rig up a bleeder valve on the top heater core line to see if I can > get all the air out. Before you go looking for that steep a hill, try this: go to your local auto parts store and get a Prestone 'flush-and-fill' kit (or the same thing under different brand names). One of the components is a tee with a cap, designed to be spliced into a heater hose. Splice that into your upper heater hose - with enough hose length that you can ensure the tee is at the highest point of the system. Fill system through the tee, put the cap on, start engine and run until fully warm, let cool off. Remove cap, add coolant as necessary, replace cap, repeat warm up/cool down cycle. If you're lucky, this will eliminate the heater core air lock that appears to be at the root of your problems. If after 3 - 4 cycles you are still getting air at the tee and cold air from the heater, the problem might be combustion gas getting into the coolant rather than trapped air. I realize that your heater temps are from the outside of the hoses - but they are still much lower than they should be - try (carefully) feeling the heater hose on your car after running it for 20 minutes! If all else fails, you might consider adding a booster pump in the heater line to assure water flow - something like http://www.absak.com/catalog/product_info.php/products_id/217 as one example, although a visit to your local bus - or schoolbus - garage should turn up a variety of available pumps and suppliers (they're commonly used on larger busses to get water flow to multiple heaters). Alan >>I appreciate all the great advise and I agree - a good shop should be >> able to resolve. However, I taken to 6 different shops over the years [quoted text clipped - 48 lines] > > Alan One thing I have not seen done, pulling the inlet and outlet hoses from the heater core and make sure that the hoses have flow and that water is flowing through the heater core and back to the water pump. If I've missed that this was checked, sorry. But the heater core itself could be blocked, or one of the hose linings could collapsed inside. SignatureFrank Tabor Bingo, gas station, hamburger with a side order of airplane noise, and you'll be Gary, Indiana. -- Jessie, "Greaser's Palace"
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