It is spraying coolant out of the cap when it does this - but the coolant isn't really that hot. It's not like it's boiling the coolant like I thought at first. It's more like there is a lot of pressure in the system and it just blows out of the cap. If there is a blockage - where does it typically occur? Would it be advantageous to backflush the system? Is there anything you can use to dissolve buildup, etc. in the coolant system?
Thanks guys

 

These systems with the degas bottles require a certain procedure to fill and purge all the air. You may simply be getting an airlock. For troubleshooting purposes, temporarily remove the thermostat, you may just be getting a batch of bad stats.

 

You are getting pressure from somewhere. I still think everyone is omitting one statement you have made. Your coolant smelling like fuel. Than is not normal.

A flush never hurts. I say, (if you feel like it for your peace of mind) GO GET A FLUSH! You know your fluids are new and DON't SMELL LIKE FUEL. Then when and "IF" this happens again. POP THE CAP AND GIVE IT A WIFF! If it smells like fuel, where could it have come from?

Go with that and see what you have after that. BUT, the fuel smell has me worried, that's all. (anyone else agree?)

 

yea if it smells like fuel there is definately a problem.

 

I am pretty sure I have at least a bit of a leak in the head gasket which is causing the fuel smell. The problem is more of a sudden blockage though like a hose collapse, etc. - I put one of the thermostat's with a giggle valve and a failsafe mechanism in last night and now it's not having the blockage/overheat problem (for now......) I will probably have to redo the head gasket before too long though. I think with the leak it's causing extra pressure in the system.
Anybody replaced the head gasket on a 4.6?? How tough a job is it and how long would it take?
Thanks

Sorry for the delayed responses - I've got four boys playing hockey this time of year and about five minutes a day to think about this problem.

 

You are at about a 90 % chance it is a head gasket, but try the cheap fixes first: New thermostat and radiator cap. If still a no-go, do the hyrdrocarbon test. Good luck.

 

I have already replaced the thermostat twice buddy - and the system was pressure tested so the cap is fine. Thanks................................

 

My bet is the water pump has lost it's impellers due to corrosoin, hence no heat and overheated engine. The only way to check this will be to pull the water pump. Since it is already off, you should replace with a rebuilt one.

I would do this before checking for head gasket problems.

 

Would this cause the coolant to smell like fuel?

 

No, but a head gasket would not make it smell like fuel either, that would occur through the intake manifold. When overheated, there are many smells and it can become confusing.

There is an obvious circulation problem, and the themostat has been changed. Now it's time to look at the water pump to rule that out. These trucks have been known to have impellers rot away

 

The mechanic told me that if the head gasket is leaking near an exhaust port the spent fuel and gases will enter the coolant and cause it to smell like fuel. This would also explain the pressurization of the coolant system I guess. I'll drive it awhile and see if the blockage issue is gone with the new t-stat.

Any of you replace the head gaskets on a 4.6? Difficult or just time consuming?

 

A simple check of the water pump could save you alot of time and money. I would do this before head gaskets. But it's your truck.

I hope you solve this problem. Good luck with your repairs.

 

arctic-

i know your pain, man! at 132,000 miles, i am having the exact same problems as you...cold air/warning lights/pegged temp gauge/shut it off, then start it back up and all is good...i've also found that you can just drive through it and everything will eventually return to "normal" after a few miles. sometimes my truck will go thru a cold air/hot air cycle 2 or 3 times before it acts right.

i explained the problems i've been having to a mechanic i work with and he said the same as yours...blown gasket or cracked head near an exhaust port...says that's the only way we're getting exhaust fumes in the coolant.

on mine, i noticed that the colder the engine, the more problems i'm having...at the reservoir, there's a lot of pressure (sometimes it blows, sometimes it doesn't), and i noticed that at least part of the time, there's not any pressure in the upper rad hose at that point. once the engine warms up enough to release whatever is blocking the flow of coolant (he used the term "air lock"), the truck runs fine, the heater works fine, and all is good until the engine gets cold again.

he says that when the engine heats up, the small crack (wherever it is) closes off when the metal expands, which is why the truck runs good after warming up and why it seems to be worse or take longer on colder days. his suggestion was to try a powdered stop leak and to trade her in.

like you, i was hoping that flushing the system was the answer, then i prayed it was the thermostat, then i was moving to the heater core, but none of those things explain exhaust fumes in the coolant. so now i'm thinking that keithhatter had it right all along. i'm headed to the parts store and then on up to the dealership while the buying incentives are still ripe. good luck ya! i need another cig!

 

I finally figured out what was causing the intermittent blockage. Due to the head gasket leak - the coolant system builds up a vacuum somehow. Each time you start it up and drive it - it builds more vacuum pressure, eventually causing the upper radiator hose to collapse and block the flow.
If I relieve the vacuum from the system after each trip i.e., open the reservoir cap - it doesn't do this anymore - not that my problem is solved by any means. Time to either fix the heads or send 'er on down the road.

 

Still not sure how coolant was coming out of the cap due to vacuum pressure though?