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Whats the signs of a bad radiator cap?

27K views 28 replies 6 participants last post by  SWINGRRRR 
#1 ·
My truck started over heating yesterday. The night before I noticed the heat wasn't blowing very hot, but didn't think anything of it. I checked the coolant the next day and it seemd fine. I'm not loosing any.
Well yesterday on the way to a BB game, my truck overheated. The gauge was in the red. I stopped, hosed the radiator down till it cooled and limped it home. I really don't think it a head gasket. I let it warm up and reved it up, no bubbles in the coolant tank. I am worried its the fan clutch. When I went fast, the temps came down. When I was idling at lights, its crept back up.

I can hear like a "tea kettle" bubbling over noise coming from my coolant cap.

Truck is an '02 4.7L
 
#3 ·
A bad radiator cap will either leak, or not open, and collapse the upper rad hose when your truck cools.

Either waterpump or thermo,.. if you turn on the heater/fan and your temps go down,.. its not the waterpump.
 
#4 ·
now that i thought about it for a min i was thinking thermostat but if it cool off when you go quicker sounds fan clutch to me see if a buddy will let you take his fan off and try it. i had to do this with a truck at work and ended up saving some money cause it was something else. Wait for some other smart guys to wake up. but i think they will confirm with me and mud here. grab it when its cool and see if it spins very easy should tell alot
 
#5 ·
I don't think its the WP. While messing with it yesterday, the thermostat opened and alot of water was pumped out with the cap off. (Stupid I know) I was trying to "burp" it with the cap off.

Thanks guys. I just figured I would check. I don't wanna throw money at it and the new fan clutch not fix the problem.

I guess I should mention that the temps fluctuate. It will be in the red, then what I assume the thermo opens and the water changes positions. Then after running again for a minute, itll warn back up, and stay hot(gauge in the red.) I think the water in the radiator isn't being cooled. If that makes sense.

I haven't gotten the courage to grab the fan with it running yet. How hot does it need to be? I dont wanna run it a long time in case is seizes or something.
 
#6 ·
Ok, now I'm stumped. I went out and let it idle for about 10 minutes. I turned the heat on and it took a long time to start feeling it in the cab. Anyway, once the temp gauge pegged out, I turned the truck off and moved the fan. I could spin it both ways.
I started the truck again, but I put my floor fan from my bedroom in front of the radiator. My temps still climbed, but it didn't peg out.


That should say without a doubt, its the fan right?

(I just don't wanna throw money at it. I'm getting married in 27 days, and I'm broke as a food stamp.)
 
#7 ·
check for play in your fan,hold it in the 9 and 3 oclock pos.and wiggle it back and forth, if alot of play, possibly the wtr/pmp, spin it and it should not make more than 1 full rotation, if it does make 1-1/2-2 rotations freely, than poss. clutch. hope this helps.
 
#8 ·
I just got back from the parts store. I took long stopless straightaways and the Check Gauges light only came on once. The temps were still high, but not bad. Once I got back home, I could hear the water bubbling in the upper radiator hose, and in the radiator itself.

I think regardless, Imma take it Wed and get them to flush and fill the coolant at Big 10.

They didnt have the spanner wrench to rent, so Imma try it with some vise grips.
 
#9 ·
I just got back from the parts store. I took long stopless straightaways and the Check Gauges light only came on once. The temps were still high, but not bad. Once I got back home, I could hear the water bubbling in the upper radiator hose, and in the radiator itself.

I think regardless, Imma take it Wed and get them to flush and fill the coolant at Big 10.

They didnt have the spanner wrench to rent, so Imma try it with some vise grips.
I have used a 12" crescent wrench,hit it with rubber mallet. use some wd 40 or equivilant. to get clutch fan off.
 
#11 ·
the t-stat neck is at the bottom and holds the tstat, did you check the stat? I think the flow is still top to bottom
 
#12 ·
Im grabbing some lunch to cool my temper right now.

I went back out there and re-checked. The hose is now slightly warm, but the other side of the stat, the block, is smoking hot. Maybe that's my answer right there. I really really wasn't wanting to open up the system, but I guess I have to.

(If anyone cares, the Hungry Man Rotisserie Chicken sucks.)
 
#13 ·
lol, I know what you mean,I just installed my efan, everything possible got in the way of mounting the brackets, take a break, its not that bad swapping out the stat. remember if you have to add water use distilled, and burp the system. the 4.7 does not like trapped air. keep us updated.
 
#15 ·
Have you had your cap tested? You can run it by any rad. shop and get it tested. Also if you want to know if your stats not opening, fill up your rad let it run with the cap off and watch the water when it opens the water will circulate across the coils.If it gets hot and the water doesnt circulate it didnt open.
 
#17 ·
'02 Dodge 4.7L. No way no how to look into the radiator.
 
#16 ·
Yeah. Good news and bad news. Have I ever mentioned how much I hate the feel of coolant on your skin? This is why I gave up the damn truck as a hobby and bought a reef tank!!!

Well I am boiling the stat right now to see if it opens. Also, more bad news. Behind the stat was a bunch of black plastic pieces. Please Please Please don't say that the WP impeller is black plastic. These pieces look like its a new break. There are sharp edges were whatever it is exploded.


Does anyone know if the WP impeller is black? And if its made of plastic?
 
#18 ·
uh oh, I dont know if the water pump blades are plastic or not. I will try and find out. :dunno:
 
#19 ·
Stats good. It opened right up. I think Im still going to go with a 180* anyway.
 
#20 ·
I just checked my service man. I do not know about the plastic pieces. but the 4.7 cooling flows from bottom to top. if the parts store does not have a 180 stat ask for onr from a 99 dakota r/t the 360. thats what I had to do to get mine. let me know.
 
#21 ·
Well It was really messed up. The impeller was separated completely from the shaft. I got it off and put back together. I'm filling it with coolant right now. All this, by myself, with a crummy work light in my driveway.

So I can testify that someone, by themselves, can change the WP, within an hour or 2.

Thanks for all the help. Tomorrow Ill take some pics and post them. Its dark out here.

I didn't put the 180* in. They didn't have one. I didn't see your post till I got back home. I think 1 day this week Imma get my oil changed and have them flush and fill the coolant. Ill try to put in the 180* then.

The guy sold me lime green coolant. Its supposed to be universal. Is this ok to put in??
 
#22 ·
I guess if it meets the same specs and its got the anti corrosion ingrediants w/ aluminum heads and all its o.k. how much was it for the waterpump? also do the 180 stat, its easy and it will help. just make sure you drill 2 1/8 th in. holes in the flat part of the stat opposite of each other, those will be your weep holes and it wont air lock on you just like the stock with the little ball valve looking thing on it. Marty at krc told me to do that and again 180 tstat from 1999 dodge dakota r/t w/360. hope your problems are solved now.
 
#23 ·
almost forgot make sure you get it flushed soon, who knows what may still be in there. swap tstat first. and they will put the proper coolent in anyway. good luck and let me know how it runs.
 
#24 ·
Thanks. I'm not putting the coolant in. I don't wanna mess it up anymore than it may be. I'm going to go ahead and flush and refill it myself on Wed. I wont need my truck till then, company car.
The pump was $66. But he let me swap for the fan clutch so I only paid $20 more with Permatex and the coolant added. My experience is that once you install a part, its yours. The guy was cool about it though. I'm going to take back the coolant I bought from them and look for the G-05 stuff. I'm also going to get the 180* thermo stat. I wanna do it all at once. Then maybe down the road do an Efan.

I used to be all into working on the truck and crap. Ive just moved away from it. Im not into it anymore, I love my reeftank more. ;)

Thanks for all your help. Its shower and Bud Light time.
 
#25 ·
amen, sounds good. let me know how everything goes w/ flush,stat, and if problem is fixed. enjoy that bud lite.
 
#26 ·
I got the lower stat and G-05 at NAPA. The stat was #169. Ill throw it and the coolant in when I get home.

Just FYI, the coolant was only $10, Zerex G-05. I got 2 jugs of it.
 
#27 ·
I'm just waiting on my RO/DI unit to make 2 gallons of water and I'm done. I drilled the holes, swapped the t-stat and away it goes.....................................
 
#28 ·
good deal, its distilled water right? glad it all went together for ya let me know how it drives-runs
 
#29 ·
Better than distill. RO/DI is reverse osmosis, de-ionized water. Its just about the purest form of water. I use it in my reef tank, so I figured why not?

I let it run for a long time with the cap only 1 turn on. It never got even 1/4 of the way up the gauge. Imma take a shower, then headed out for wings when momma gets home. Ill report back in a bit. (If Im sober)
 
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