2000 4.7 cooling system problem
 

Hi there,

new member trying to get some help with a problem. I searched for "thermostat" and looked through a bunch of old posts, but none seemed to answer my question

which is - no cirlucation, pressure builds up and "blows out" the connection on the upper radiator hose between the hard plastic pressure relief valve and the short rubber hose.

I have 2000 Dakota 4x4 4.7L automatic tran

truck has been running fine till last week or so. drove 130 miles to go rabbit hunting, then on the way back after 15 miles or so (60mph), that connection leaked coolant, steam all over. I repositioned the two pieces, duct taped and drove 110 miles or so home. drove to work a couple of days later, 5 miles, and that same thing happened. re-taped, and parked. driving home, made 3 miles and saw the temp gauge going way up - pulled over and let it cool; drove another mile and the tape blew out again and temp went way up - added some water, waited for it to cool to mid gauge, and made another mile before it happened again. - repeated that the next mile, and finally made it home.

since I had no hot temp issues earlier, and not much heat from the heater, I'm thinking that the likely suspect is a stuck closed thermostat - that would cause no circulation, pressure build up in engine and a blowout on the return to radiator?

anyone else ever have this happen ?

I'm planning on replacing the thermostat as the easiest thing to try - think I have to move the alternator to do that and will check the water pump for wiggle factor then.

and a last question - in one of the threads I searched, comment was made to NOT use the radiator drain plug (likely to break it ?) but to just pull the bottom hose and drain from there - that sounds real messy to me - is that a recommended thing, or should I use the radiator drain plug like I'm used to doing in other vehicles ?

thanks for any help or suggestions

mat

Welcome to the forum Matt.

You don't need to touch the alternator to change your thermostat, it's UNDER the engine, right where the lower radiator hose goes. So, you may as well just pull it, messy as it may be.

There are two bolts on the thermostat housing. Be very careful as they can/will break. I'd suggest some penetrating oil on them a day or so before you touch them.

Get the thermostat from Mopar. There are a lot of crappy parts lately and you don't need/want to do this again. It's an easy install though. It has an o-ring on the thermostat and it just sits there. No gaskets needed.

I attached an image for you.

Do you have the Factory Service Manual? You can download it from the sticky above.

no, I don't have a factory service manual. do have a Chilton's manual about an inch or less thick. there were maybe two or three sentences in there regardign thermostat - that's where it said that I probably would have to move the alternator.

thanks for that diagram - from that picture, it sure looks like I would have easy access. I haven't crawled under the truck yet since it was still dripping and snow on the ground. I'm going to look at it today and try to do the work tomorrow.

I'll look for the factory manual and download it - I,m certain it would be more helpful than that Chilton's book

thanks for the help

Matt you should also replace or have the cap for the coolant checked.

Being a 4.7, my first and only thought is "blown head gasket".

Replace the upper hose (mine came apart in the same spot, a very big mess!), replace the stat, and run the engine up to just below operating temp with the cap off.

Just re-reading the OP, a stuck closed thermostat should have given you LOTS of heat.

You might want to get a combustion leak detector kit. It can help pinpoint a blown head gasket.

The water pump can fail too, as can the cap.

Well, I changed the thermostat (which looked OK, and replaced the upper hose unit.

couldn't get any circulation in the cooling system after that - nothing moving out of the radiator, even after the temp went past 190 to about 3/4 on the gauge

pulled the "coolant bleeder" plug and that didn't help at all - thought it might have gotten air bound.

seems to me that even if the water pump wasn't working, there should have been some coolant moving into the engine ? don't know? thought about pulling the water pump - but didn't

so I gave up and took the truck down to a repair shop, and i'll let the mechanic figure it out

thanks for the help - I'll update this later when I get the diagnosis

truck has 255K on it, and I don't really want to spend a lot of money on it.

The impeller on the water pump can corrode over time. When that happens eventually no water flows.

Bugs Bunny's revenge? JK, I hope the fix is a simple one and not head gasket. Was the water pump weeping or making any noise?

We've got exactly the same mileage (need to update my sig). Interested in seeing how this turns out. When I bought the truck, I replaced thermostat and radiator. Also flushed with distilled water and Prestone radiator flush a few times.

" hope the fix is a simple one and not head gasket. Was the water pump weeping or making any noise? "

no, there was no indication that the water pump wasn't working - might not be any maybe, if the impeller was worn out

whatever the initial problem was, it seems now that the radiator is likely plugged up - when I pulled the bottom hose, not much fluid came out, and after I finished and was going to fill the radiator, it was still mostly full, so it seems to be plugged ?