overheating, loss of antifreeze

I have seen similiar posts but just for kicks here I go. 1997 venture with 125,000 miles has been using antifreeze for about a year but now uses a large amount, appx a half a gallon every two weeks. Never could find a leak, even the local garage finds no evidence of a leak. Also my venture now overheats (red zone) and when I turn on the heater I get cold air. The temp gauge goes from hot to half and back as I drive. I replaced the thermostat and flushed the system already! From similiar posts I suspect the head gaskets are bad. A mechanic tells me that the reason I do not see a leak or evidence of a leak is because the antifreeze that I,m using is getting burned up and going out the exhaust. No white smoke or any smoke and the oil on the dip stick looks good, no foam or anything out of the ordinary. Also what would a repair (head gaskets) cost at a garage and any other suggestions would be greatly appreciated. Thanks in advance

Head gasket would be what I would suspect. You don't have heat as you have air pockets in the cooling system. If you want to confirm it, you can by a chemical antifreezer tester to check for exhaust gases in you coolant. A pressure check also confirm it, but if it only leaks when warm it may return a false negative. Another thing to check is that when the engine is hot, look at the overflow tank. If it's overflowing, you have a head gasket problem.

Check out this thread (http://www.automotiveforums.com/vbulletin/showthread.php?t=476824) with someone who had the same problems. I gave some help to them that applies to you as well. It also links to a few key threads that will be helpful as well.

Try this on for size. Im betting that its not the head gaskets. I think you have got a bad intake manifold gasket.

Ive seen this before. The intake gasket fails where the coolant passages come in contact with the head. It can leak externally and be seen or leak internally and not be seen. If its bad enough and also bad around the intake runners, the coolant can get into the combustion chambers and burn off.

When I first head this I thought B.S.! I had a 2000 chev malibu loosing coolant externally from the intake gasket. It was also fouling out two of the spark plugs on the front cylinder bank. They were white and chalky. I first thought oil consumtion, so I did a compression test and found low compression in those cylinders. I was completely prepared to put in a new motor. An older and wiser mechanic told me to do the intake first and see what happens. I did and problem solved. No more coolant loss, no more fouling plugs and afer a bit, no low compression.

Check your plugs and do a pressure test on your cooling system. Your loss of heat could be as simple as low coolant. No coolant through the heater core = no heat.

It is possible that the intake manifold gasket is leaking. However, he is also getting symptoms with rapidly fluctuating coolant temps. That is indicitive of large air pockets in the cooling system. There really isn't any way for air to enter a pressurized cooling system other then being forced in. The easy way to tell would be to run a chemical test on the antifreeze looking for exhaust gases. It's available at most autopart stores.

I hav a 1999 Chev Astrovan. I was getting these same symtoms. It turned out that my intake manifold gasket had gone. I was getting coolant into the engine oil. They replaced the intake gaskets and the next day the engine started to rattle to beat the band. Told that the main bearings were gone. I now need the whole engine pulled and rebuilt. If your looking at getting the head gaskets done, you may as well have the whole engine rebuilt, about $500-$800 more. If you get that damm Dexcool into your engine oil, pretty much can guarantee an engine overhaul.

It could have started as an intake manifold gasket issue and then cause issues with the head gaskets. I have a 98 Trans Sport. I recently installed a new engine with the same issues. I a little coolant at first, then I let my brother borrow the van for a bout 6 weeks and I forgot about the coolant issue. My van was returned to my with a rollback pulling up in my driveway!!! He drove the van with it overheating. I started it and it ran ok until the water started to flow through the engine and then came the fowl smelling white cloud of engine death. I replaced the 98 engine with one out of an 04, with a few changes to the 04's engine, it runs way better than the 98 had ever ran. There are two morals to this story. One - never let your brother drive your cars, and two check for the intake manifold gaskets at forst sign of a leak you cannot find externally...

I have seen similiar posts but just for kicks here I go. 1997 venture with 125,000 miles has been using antifreeze for about a year but now uses a large amount, appx a half a gallon every two weeks. Never could find a leak, even the local garage finds no evidence of a leak. Also my venture now overheats (red zone) and when I turn on the heater I get cold air. The temp gauge goes from hot to half and back as I drive. I replaced the thermostat and flushed the system already! From similiar posts I suspect the head gaskets are bad. A mechanic tells me that the reason I do not see a leak or evidence of a leak is because the antifreeze that I,m using is getting burned up and going out the exhaust. No white smoke or any smoke and the oil on the dip stick looks good, no foam or anything out of the ordinary. Also what would a repair (head gaskets) cost at a garage and any other suggestions would be greatly appreciated. Thanks in advance
Just had both head gaskets done on a 2000 venture. also heads were planned. had dealer replace spark plugs. 1500 dollars.

It could have started as an intake manifold gasket issue and then cause issues with the head gaskets.One does not cause the other. They are independant failures but many times people associate the head gasket with the intake gasket leak because they are similar in symptoms as well as you have to do the intake gasket when you do the heads.

I replaced the 98 engine with one out of an 04, with a few changes to the 04's engine, it runs way better than the 98 had ever ran.
kc9dre - Do you mind sharing some of the changes you ran into when you put in the 04 engine? I know the cam sensor changed designs around 2000, and I've read there were different injectors & intake manifolds at some point as well, but there's likely more than that, and have yet to find the specific differences in revisions of the 3400 spelled out anywhere online.

I might be doing a similar swap in the not too distant future and am trying to find out specifically what is and isn't a direct swap when putting a newer style 3400 into an older model...thanks for any advice you might have!

". . . I was getting coolant into the engine oil. They replaced the intake gaskets and the next day the engine started to rattle to beat the band. Told that the main bearings were gone. I now need the whole engine pulled and rebuilt. If your looking at getting the head gaskets done, you may as well have the whole engine rebuilt, about $500-$800 more. If you get that damm Dexcool into your engine oil, pretty much can guarantee an engine overhaul.

"The next day the engine started to rattle, . . . told the main bearings were gone." Sounds fishy to me that they weren't rattling before the gasket was replaced and there is no reason for the bearings to start rattling after they replaced the gasket. Maybe they messed up installing a lifter or valve and it was rattling.

The intake mainfold replacement deals with the "top end" of the engine while the crank shaft main bearings are in the "bottom end" of the engine and repairs to the top end should in no way effect the botom end.

If you get coolant in your oil the level of damage it does depends on how much coolant, how the vehicle was driven, (fast/interstate being worst), and how long it was in the oil before you caught it. I make it a habit to check all fluid levels in both vehicles every Saturday morning so if a fluid level or it's appearance isn't right it's not long before I find it.