Autozone will have the blue block test fluid in stock later today, so I'll post again after I've run the combustion leak test. Until then here's my summary so far:

- replaced CHT sensor
- drained old coolant and flushed the system
- replaced old thermostat with a new Stant 195 degree unit
- refilled with 50/50 mix of Zerex G-05 and distilled water
- installed Prestone Flush and Fill tee in top heater hose
- installed a new coolant overflow pressure cap
- purged air from the system at cap and tee

The truck seemed fine for 1-2 days after all this. But then I noticed no heat from the blower followed by a temperature spike and coolant forced out at the pressure cap. These temp spikes do not last long (usually 15-30 seconds) before returning to normal. When this happens I just continue driving, and another temp spike / coolant loss event may or may not occur before I eventually turn the truck off.

After I let the truck cool down completely I will restart it (cold idle) and replace the lost coolant while burping the system. Then the "no heat / temp spike / coolant loss" sequence will normally happen again after the engine reaches normal operating temperature and stays there for long enough. Or maybe it won't happen on my first trip after the refill-and-burp but it will happen on the next trip.

---

If it weren't for the inconvenience of refilling coolant and purging air every day before I drive it, I would just live with the occasional temp spikes. They have not yet hit the red zone, and so far they haven't lasted more than 30 seconds or so.

If only I could retain the coolant within the system that's currently being expelled out the pressure cap, I might see a gradual drop in coolant level over time like mbb did. But this is not possible when some coolant is lost each time the temp spikes.

I've tried smelling for a "sweet smell" or a "coolant smell" at the exhaust but so far I don't detect any. I see steam (white smoke?) from the exhaust at cold start, but I think this is normal until the engine warms up.

 

Take a look in the engine cavity. Shine a flashlight down in the cavity behind the Alternator. See if it collecting coolant on top of the block.

Any white smoke, how does the exhaust smell ? It has to be going somewhere and there has to be evidence of that.

 

This...

 

Which part?

Well everyone is saying Hydrocarbon test so you must mean the seal. Could have something to do with it. If it's the pump, I'd lean towards a "no circulation" problem...no prop, no circulation which can screw everything up. That's a common problem. Parts of the system are being skipped, the pump should be evaluated always IMO.

Seems like with a lot of these types of threads lately, no one is checking the pump. I've seen the props on these pumps wear down to nothing with the bearing remaining perfectly fine. You can't tell unless the pump is removed for inspection.

 

WOW! I never heard of that, but I don't know it all.


I am thinking more of a HG problem as once it 'burps' things seem to work OK which would suggest the pump is probably doing its job but there is an airlock in the cooling system - be it in the jacket or heater core.


The other possibility is that when the coolant was replaced, the OP did not warm the truck up enough to open the thermostat and created an air lock in the cooling system.


Either way, hydrocarbon tests are cheap and definitive.

 

I knew I'd get crap for suggesting the bars but it's what worked for me. I did it last december exactly as the directions said and it's been fine for almost a year now. My heat works fine and I left it in without flushing it out. It's not the same crap from years ago. I spent over $800 testing, changing parts, flushing, and 3 different garages were stumped. On the bottle it had my symptom of air getting in cooling system and making the coolant go out the fill bottle, so I said what do I have to lose, AND IT WORKED! I'm disabled and don't have a couple grand to put in an old truck. Even if the thing started doing it again, I got almost a year out of it for $30-$40 Sure better that $2000+ then have the darn tranny go out or frame snap from good old rust rot. If you can afford to get the heads done or a rebuilt motor, go for it, it's the best way and if I had the money I would have done that too.

 

I ran errands around town and on the freeway for close to an hour today, all without a hint of overheating (although there was plenty of gurgling in the heater core). My last errand was to pick up the Block Test Kit from Autozone. I took it home and ran the test, but after almost 10 minutes of pumping air through it from the overflow reservoir the only color change was from blue to blue-green ... certainly NOT yellow!

I pretty much expected the fluid to turn yellow, but when it did not I took the tester to my exhaust pipe ... and within 3 bulb squeezes (2-3 seconds) the fluid had absolutely turned yellow. At least this confirmed that the fluid was working properly.

Then I washed out and blew dry the tester as instructed, and I tried the test again on my cooling system, this time for only 2-3 minutes. The fluid started changing from blue to blue-green like my first test (and apparently this is to be expected according to the instructions I attached at the bottom of this post) but I still wasn't seeing any yellow. Not seeing yellow test fluid on my hot engine tests is encouraging, but testing the engine while hot is apparently not definitive. Now I'm waiting for the engine to cool completely before I run some cold and warm engine tests.

Jbrew, there's nothing leaking behind the alternator. I checked that area thoroughly when I had to get in there to replace the CHT sensor. That whole area is basically clean and bone dry. In fact, the entire exterior of the engine does not have any leaks -- which is somewhat strange given the fact that most of the vehicles I've owned over the years have shown some signs of current or former leaks.

So if my cold and warm tests fail to indicate hydrocarbons tomorrow, would this be my "next step" in the diagnosis of the problem?

Question: Since I cannot find any valves on the heater hoses, does this mean coolant is constantly being pumped through the heater core? Or does the heater core itself have a valve on it?

I wonder if a bad pump is causing the gurgling in the heater core because it's not strong enough to force coolant through the heater core and "fill it up" while pushing the trapped air along until it gets to the radiator / overflow tank?

Here are the Block Test Kit instructions for reference:

 

NOT a HG problem.


AFAIK and remember, the heater core always has coolant inside. The 'trick' of the climate control is that unless it is winter, the coolant does not move and therefore stays cooler.


This commonly can cause a air lock problem. Here is a suggestion you are welcome to snear at or try as you see fit. It is what I used to use to verify my work when I was pretending to be a technician at a dealership.


When replacing the thermostat or water pump, my final test was to run the engine with the radiator cap OFF so I could see the coolant begin to move which is evidence the thermostat has opened. At that point, I would get in and put the heater to max and continue to idle the vehicle for 5 minutes with the cap still off. Then let it cool down a bit and make sure you have enough coolant and put the cap on.


All that SHOULD get any air out of the heater core and probably will allow any air lock to 'release'. Some vehicles would get problems if the lower radiator hoses were replaced.


YMMV

 

White smoke upon cold start, none at any other time. Exhaust does not smell sweet or antifreeze to me.

Maybe it's not going anywhere. Maybe I'm not actually losing any EXCEPT for the times when it gets blown out the overflow. Unfortunately it blows out the overflow almost every time I drive it. Today was an exception but I don't have a clue why.

If I could go for a week or a month without having any coolant blown out the overflow, I might be able to see the level changing (or not changing) over time. But as it is there's no way I can compare coolant levels from one day to the next.

If the head gasket leaks only when the engine is cold, this might explain why there's no white smoke after the engine warms up. Unfortunately my nose is not that great so maybe other people could smell the antifreeze in the exhaust after a cold start even though I cannot. Is there a test (other than smell) to detect antifreeze in the exhaust?

 

You can look in the coolant reservoir till the cows come home on these trucks, the fluid doesnt flow thru the reservoir, you arent going to see anything move.

You could touch the hose leaving the tstat however for it to feel warm.