So I towed my new travel trailer from Long Island to Lake George. The truck ran great, no issues. When I got home I checked to degas bottle just for the sake of checking and it had puked a bit. It could have been from a slight overfill of coolant as I recently did the lower radiator hose.

So I decide to do some head gasket testing by putting my gauge on the degas bottle.

What I found has me a but confused.

I drove the truck until it was up to full temp. Coolant pressure was about 8 psi and never got any higher no matter how I drove it.

I vented the pressure and started driving again. This is where I get a bit confused. I would get on it and "drive it like I stole it". I tried the highway and long straight secondary roads. No big hills like in the Adirondacks but I did my best with the small hills we do have. When WOT I would see an instant increase of 1-2 psi and as soon as I let off the psi would drop back down. The pressure never went over 3 psi no matter what I did. After about 30 minutes of driving, after venting the psi when at operating temp, I did manage to build 1 2 psi in the system total.

I would imagine if it were head gaskets then the pressure would continue to build. I am guessing the water pump creates a bit of pressure when engine rpms go up but it is just a temporary spike.

I have to do some testing with the trailer next week, and will run the pressure tests again but thought I would post and see what you guys think thus far.

 

Was the cap pressure tested? It should be holding 12 pounds.

 

I did not test the cap yet. But there was no puking during my testing today.

 

I assume this is supposed to read 1-2 psig? Not 12 psig?

I ran the same test you did a year ago after I got my pressure gauge plumbed in. Mine is in the extra port on my coolant filter. I noticed a 1-2 pressure increase as soon as I gave it throttle. I couldn't get it to go any higher after 45 minutes of mixed interstate and highway driving. So I assumed things were good.

I do see 16-18 on the gauge when towing, but it is very temperature dependent. I'll typically approach 16 psig at 207-210 coolant temperature. I've crested a few hills with the fan going, and I'll have coolant temperature back down at 195 at the beginning of the next hill, and pressure will be back at the 10-12 range. Then I'll hit 20 psig of boost and watch temp/pressure climb during the next hill - but pressure remains very dependent on temperature.

I do see a couple psi higher on my gauge when towing versus unloaded at the same water temperature. I have not figured this out yet. Thought it was maybe EGT-related in the EGR cooler, but it occurs before EGTs really get going. Thought head gaskets, but when the fan knocks down coolant temp, pressure will fall with it, regardless of engine load. It could be higher flow through the coolant filter or something downstream of it, but haven't investigated that enough. Haven't really had enough concern to do so.

Probably left you with more questions than answers. What max coolant temp did you get to on your tow? Mine puked on a trip where I hit 220 once or twice.

Mike

 

There's two things that happen in a closed cooling system, coolant expansion due to thermal increase, and I believe as Rick point out a while back, vapor pressure at different temps.

 

It doesnt seem like you have an issue but would be good to verify the cap is sealing properly before testing. For some background, mine runs ~8psi when warm. Going up a large hill will cause an increase to ~11 (from extra heat generated) then drop down the 8 range after. Also pressure stays on the system over the course of a few hours until it slowly drops with engine cooling. If your proessure drops quickly after turning off, you may have a bad cap which will cause all readings to be off.

 

I would replace the degas cap. It is about $6 on amazon. Otherwise your pressures sound fine. When my head gaskets blew last year, I would build pressure to over 15 psi in just a short drive. There was only a small blowout at #6 when the heads were inspected. BTW I tried the exhaust gas test kits and they are never positive. The pressure testing is the best way. I tee'd it off the hose on the degas bottle and ran it into the cab. Took less than 5min of driving to confirm pressures were too high.

 

I agree with the guys as well. get a new cap and then retest. Pressure should not drop down fast at all when letting off throttle.
Should build as temps come up and then top out from thermal expansion.

WOT inputs should slowly build a few psi at first and then stop once engine is at top temps.

 

New cap on order. I hope to get some more testing, while towing this next week if not this week.

 

Don't create a problem while trying to find a problem that ain't there!
I think you're fine and you just need to run it and enjoy.

Where did you stay, in a campground in Lake George area? If you didn't already, you gotta check out Ausable Chasm. We stayed north of George in North Hudson @ a Yogi Bear. Good times!

 

Roger that.

We were at Lake George RV Park the last week of August. Had a great time!

We did Jellystone at Birchwood Acres 2 years ago. Top notch place for the kids.

 

Towed the trailer this weekend. 12psi max with the trailer. Same drive without the trailer was maxed out at 12psi as well. Granted, it is not towing the the Adirondacks but I am happy for now.