94 Grand Caravan 3.3L Overheating

[pgn674]

I have a 1994 Dodge Grand Caravan SE with a 3.3L engine that's overheating.

It's summer right now, with temperatures around 75 here. After driving for some 10 minutes, the temperature gauge with gradually rise up, and instead of stopping at 1/2 as normal, it will continue up, going all the way to the top so the "CHECK GAUGES" light will light up if I keep driving. I've noticed that the air system will give me no heat at all in the cab when this happens. About a quarter of the time, though, it won't over heat, and I do get heat form the air system, and I can get to wherever just fine. This all seems to be happening despite all the repairs I've tried.

I've replaced the thermostat (twice, the first one didn't have a bleeder check valve). I've replaced the radiator cap. I've got the pump sitting out on my drive way right now, and that looks fine, though I'm putting in a new one anyways. Plus one of the bolts just broke; that's gonna be a pain to drill out -_- And, each time I think I've bled the system OK, plus one time I made sure the coolant came up to the thermostat before putting the radiator pipe back on. The radiator pipe is the rubber pipe that's on the top side of the thermostat and that goes to the radiator, right? The radiator fan is starting and stopping when it should.

Oh, and, one time when it over heated, I pulled over, checked the radiator pipe and it was cold, waited 5 minutes, checked again and it was hot, and I went on my way and got heat from the air system and the engine didn't over heat again. The next day, the same thing happened, but when I continued it overheated again and I got no heat from the air system. Gah, it's so inconsistent Oh, and that time, even though the radiator pipe got hot after I squeezed it a bit and felt fluid trickle through, the radiator, just 1 inch away, stayed cold, even after running the engine again.

And, one more thing: I got the radiator replaced by a garage 4 months ago, and this has been happening for almost a month.

So, maybe it's a clog? But aren't clogs pretty definite, not intermediate, so that when one happens, it breaks and stays broken? I get the feeling that when it's overheating, the radiator is cold as ice, but when it's working, the radiator is a hot as it should be. Maybe I haven't bled the system right? Anyone have any ideas? Thank you!

[KManiac]

Sounds to me like you have either a bad head gasket or a cracked cylinder head, causing exhaust gas intrusion into the cooling system. Accumulated exhaust gases in the coolant will cause a bubble behind the thermostat, resulting in delayed or no thermostat opening when the engine is started from cold. Buy yourself a "Universal Block Tester" from a local auto parts store and test for the presense of exhaust gases in the cooling system. Let us know what you find.

[pgn674]

Ugh, yea, that would explain it. Plus, there was one thing I forgot to mention: When it over heats, my coolant reservoir fills up, some times to a slow over flow. And, after the car has cooled, the reservoir is still full. Made bleeding and filling the system pretty difficult to understand.

So, my dad and I are going to put everything back together and run it without a thermostat. He thinks this will tell us if it's a gas leak in the block or not. If so, and if the leak is insignificant enough (unlikely), we'll find a way to get the car to last the summer until fall (with minimal use), then junk it. If we still can't figure it out, we'll try that Universal Block Tester.

Thank you for the reply, and I'll let you know what ends up happening.

P.S. Last summer the car's transmission over heated every once in a while, and the engine might have gone with it. To add tragedy to this story, I just had the transmission rebuilt 4 months ago. Cost almost $2,000, and I'm pretty sure I got gypt on the price. I just needed to get back to campus, and so let them do the work. Ugh, oh well, live and learn and tell others about it, I guess.

Maybe there's a way to sell a newly rebuilt transmission with a 2 year warranty? Might have to look into that.

[pgn674]

Alright, so I put everything back together, with no thermostat, filled it with coolant, and started the car. As it ran, I put in more water, and looked closely. It was bubbling up. Once it was full enough to have water visible in the coolant filling place, I saw that some gas was coming out. Smelled it; it's exhaust.

So, I have some head cracked, probably cracked last summer and has only now become a problem. But, the radiator and the radiator pipe both got hot pretty quickly this time, so it seems the over heating problem is gone. It was probably exhaust getting trapped under the thermostat and preventing it from detecting hot coolant.

So, now I guess I drive it here and there on non-critical errands, and see how it runs. And, look into getting another car. And figure out what to do with this one once it dies for good.