Hello all,

So I recently replaced a cracked intake manifold, which really was not that hard to do. I also changed all the plugs and igniters as they were close to due. I changed the original 18 year old thermostat and drained a good amount of coolant out, but not all of it, and obviously refilled that. I drove it a few times and the coolant level went down, I figured this would take care of any air, but last few times it has not gone down any. I figured it would take care of itself, but it hasn't. Right now I don't really have heat. The engine is running at normal temp, and first time I turn on heat when engine is warm, I get hot heat, but it only lasts about 10 seconds then gets colder and colder pretty quickly. Heat lasts a little longer if I am stopped. If I turn the fan off for a few minutes, same process repeats.

I am guessing air is trapped in the system, what is the proper method for purging or "burping" the system? I have read posts that say to run it at idle with heat on full blast to burp it, and other posts saying to remove the apparently fake vent line at the reservoir. Has anyone done this before and can give advice?

If I had taken that job in Hawaii, this wouldn't be a problem, but unfortunately right now in the Midwest, it is.


Thanks.

 

 

 

No, it's the 5.4 (still fairly mighty), and I meant the coils, not sure why I said igniters.

 

Thank you! Yes, I suppose I should have mentioned that. It's the 5.4.

 

How often is "close to due"?
I haven't seen a recommended change interval for the COPs.
The coils will last a lot longer than the boots, the boots degrade over time making it hard for them to contain the spark voltage.
I change plugs & boots at 50k.
You might have a restriction in the heater shutoff valve allowing only a small flow of hot coolant thru it.
Have you felt the hose after the valve to see if it is hot, or use one of those IR thermal guns, they're fun to play with.
Has anyone used an IR thermal gun to look at exhaust manifold runner temps to find a misfiring cylinder?

 

The spark plugs, coils, and boots were all replaced at 100k, which was like 09 or 10' if I remember correctly. I was planning on doing them again at 200k but since I had the top of the motor apart, I figured I'd do it while everything is apart. The plugs were worn, but not burnt or fowled. The coil boots were fine on most cylinder, but had turned a lighter gray color. The coils for cylinder 7 and 8 were getting the coolant leak onto them, and 8 had basically come apart, the spring stayed on the plug and once out, I could easily tear the boot by hand. I'm not sure if that's the recomended service interval, but it's never caused me problems, it's never fired a plug out the cylinder like so many apparently have, but I use a torque wrench to put the plugs in at 8ft-lbs.

I think there is an IR gun around somewhere, I'll try that, and I'll try feeling the hose after I drive home tonight. As for the manifold, if the cylinder is missing it should not be putting out as much heat, but I'm not sure if that part of the manifold would stay cooler, or just be warmed too much by the cylinder's next to it?

 

So to update I did try the cap off the truck, and idle it. I ran it at idle until warm with the defrost at max, but nothing really happened. I never saw any bubbles at all. But since then I have been driving it around, again, it will have hot heat momentarily, but now that hot heat lasts probably 30 seconds before cooling to "warmish" air. its been from 20-30 outside recently and it seems to blow out that same "warm" temp regardless of how cold it gets outside. I know it's hard to describe without feeling the air, but I can tell it is warming the air. Before changing the manifold and draining coolant out, it had very hot heat, like it had always had, I've never once had heating issues with the truck. I should have measured how much I let pour out, but did not.

I have read through the manual and I can't find it mentioning how to purge air out. I am guessing air is trapped in the heater core, or somewhere in the system. I do not believe my heater core is plugged/bad or the blend door is stuck because like I said, heat was perfect before. I did notice my heat beginning to be less warm and wondering what was causing that right before the engine started misfiring and I realized the intake was leaking, perhaps air got in then? I had to drive it about 300 miles with the bad intake to get back home if that's relevant info.

Can anyone help, I have never had this issue before

 

You may want to revisit those loose spark plugs and tighten them up a whisker , factory torque spec for the earlier style heads was 11 ft/lbs and the later updated heads with more plug threads was 17 ft/lbs. Many of the DIY owners here have gone with increased torque over those specs with good results, up to 22/24 ft/lbs for the older design heads and 28/32 ft/lbs for the later version heads. (these numbers are for the V-10, but I'm pretty sure the V-8 shared the same values). The low factory torque spec is partly to blame to for some of the plug blow outs on the early heads, going with a lower torque value like you have mentioned doesn't sound like a very good idea. You didn't mention what year your 5.4 is.

Have you tried burping the cooling system via the hose removal like the linked thread describes (again, the thread is about the V-10 but does the V-8 have a similar manifold hose that can be vented?)?

 

When I flushed the system on my truck I refilled and left the cap off of the degas while the engine got to temp and the engine fan kicked over a couple times at the same time the heat was on hot but the blower was off.

Some have done a reverse heater core flush, I didn't need to. As WE3Zs mentioned earlier you can try the burp method in the tech folder or link Tom earlier provided.

Another option may be running cardboard in front of the radiator or some blockage in front of the grille to keep the heat in.

Which kind of coolant are you running? What thermostat brand and temp? Are you monitoring with something other than the factory in dash temp gauge?