Engine ran rough and now wont start up?

Hi Again and thank you, we did replace the fuel pump along with the computer and a few other things I am not sure of. The van starts right up now and has full power, no hesitation it runs great, but guess what now it has a new problem. While driving the temp guage will go all the way into the red then drop back down again to normal. Then back to the red, when I looked under the hood the antifreeze in the reserve was boiling but it did not overheat to the point of smoking. I drove it about 30 miles last night and after the back and forth with the temp guage it finally stayed on red but no overheating smoke. I put the heat on and it was not very hot, then would get cool than warm again. I did smell antifreeze. Now I do realize that this may be the heater core but my question is this. While driving the 'low coolant' light came on and off, then the temp light came on and off, then when they both came on together it was almost like the van stalled for about 10 seconds, when pressing the gas I barely had excelleration but it DID NOT stall and did maintain its speed. After the 10 seconds the temp Guage dropped back down to normal range and wham I got my power back and was able to accelerate. Then the temp guage went back up and both lights came on and off but still no overheating smoke. By this time I had turned the heater off. I never stalled or had to restart the van it just came back on its own. Would the Heater Core cause this? I did change the thermostat last week and flush the radiator and put new antifreeze in. Oh also about 1 month ago we smelled the antifreeze and saw it kept going down a bit so we put the Bars Leak Core sealent in it thinking at that time that it may be the Heater Core. Could it just be a clog Possibly, Hopefully? Thanks For The Help.

I have had similiar problems. But mine was my freeze plug that kept mine overheating. Check that too

I have a 1999 cheverolet venture and it wont start either. It will crank over but it wont start. I cant figure out what is wrong with it either. I thought maybe it was a starter coil pack. But im not a mechanic.

I have a 98 chevy venture that did the exact same thing, and it drove me crazy when I knew the fuel pump was still good, and I traced the wire and plug in connector along the drivers side mounted on the frame just underneath the drivers side seat and found that the plug connection which also runs the fuel gauge was nasty, wet, and corroded, I unplugged it and squirted some backing soda several times up in the prongs [and flushed it with straight water], and took a small piece of wood fingernail file and ran it up and down all the prongs, and the van starts great again and fuel gauge does not fluctuate. There is a name for this wire connector but I can't remember it but advanced auto parts, or any other place would propably know, if you show them. After I cleaned it up I let it dry good and wrapped it up in electrical tape as these vans rust very badly along the lower kick side panels and take on alot of splashing water and winter salt. Try this and you will propably find your problem. Hopefully, but I'm glad I checked as it cost me 10 cents worth of good electrical tape. AMEN.