Where is my coolant going?

[Brando_SLT]

Hey everyone - so interesting scenario with my 2005 5.7: About 2 months ago I replaced the thermostat and CHT/coolant temp sensor as my truck was getting to the 2/3 to 3/4 temp in normal stop & go traffic. Everything ran great, I towed a trailer up to Redwoods park and back to Orange County and only got to the 1/2 way mark while climbing the grapevine (I5).

Back to this week: Driving to work on Thursday morning it was about 75º F outside, cruising on the freeway at about 70mph my temp gauge was at 1/2-way. This is about 210º based on the old thermostat but I installed a 160º thermostat so I should be around 160-170º cruising. I take off the radiator cap Friday morning after letting the truck cool overnight and notice there's a big 'ol air gap at the top of the radiator. I have used the vacuum-fill method twice with a special tool. The system held vacuum for over 5 minutes when I was filling so there are not leaks that I can detect.

I crawled all over the engine bay ad under neath, looking for any sign of a coolant leak - I can't find anything. No soot or smell in the coolant either so I don't think there's a head gasket leak. No coolant smell or steam in the exhaust.

So... Where the heck is my coolant going?! Help?

 

[Bloody_Knuckles]

Did you fill the overflow tank to the proper level? Coolant expands and goes into the overflow tank and then the engine cools and pulls it back into the radiator.

 

[Brando_SLT]

@Bloody_Knuckles indeed I did, up to the "cold" fill line when I refilled the whole system. I find it odd that the coolant level in the reservoir/expansion tank hasn't changed either.

 

[Bloody_Knuckles]

Maybe there was air in the system. Monitor for awhile.

 

[Brando_SLT]

I just topped it off with the vacuum filler. It held -12 hg/in for 5 minutes with no bubbling or gurgling noises. It took about 1/3 a gallon to fill it up. Ran it for 20 minutes after and the temp guage held around 165°. I'll keep an eye on it for the next month or so. Still can't find any coolant leaks.

 

[Fast69Mopar]

I just topped it off with the vacuum filler. It held -12 hg/in for 5 minutes with no bubbling or gurgling noises. It took about 1/3 a gallon to fill it up. Ran it for 20 minutes after and the temp guage held around 165°. I'll keep an eye on it for the next month or so. Still can't find any coolant leaks.

Do a block test to verify that there is not any combustion gases in the cooling system. Just because the coolant doesn't smell or it's physical properties haven't changed doesn't mean you can't have a leaking head gasket.

It's a simple test and it's cheap enough to help eliminate a head gasket problem from your diagnostics and mislead you to other repairs.

 

[Brando_SLT]

Thanks for that insight @Fast69Mopar - I just ordered a block tester kit. If there is a leak... It might be time to plan upgrades

Do a block test to verify that there is not any combustion gases in the cooling system. Just because the coolant doesn't smell or it's physical properties haven't changed doesn't mean you can't have a leaking head gasket.

It's a simple test and it's cheap enough to help eliminate a head gasket problem from your diagnostics and mislead you to other repairs.

 

[Bloody_Knuckles]

A quick way to determine if you have a leaking head gasket is to fill the radiator when the engine is cold and start the engine with the radiator cap off. If the head gasket is leaking, you will see bubbles coming out of the fill neck.

 

[Fast69Mopar]

Thanks for that insight @Fast69Mopar - I just ordered a block tester kit. If there is a leak... It might be time to plan upgrades

Good idea. If you don't want to wait for the online order you can pick one up at your local Napa or O'Reilly Auto.

 

[Brando_SLT]

So 5 days in after topping off the coolant system - no change in coolant level (still full). Temp gauge is staying at 1/3 (155º-165º F) consistently. I am hoping (knock on wood) it was just air working its way out of the system when I did a full flush.

 

[Brando_SLT]

2 weeks since topping the coolant up - no further issues with coolant disappearing. Looks like it was just air in the system that needed to be bled out.

 

[JohnnyMac]

Thanks for the follow up. Glad to hear it! But don't let that stop you from mods....

 

[Brando_SLT]

Well, f**k. Found out where my coolant is going. Any estimates on what a head gasket job would cost? Unfortunately, not a job I'm able to do at my condo.



Most recent symptoms (besides missing coolant), hard start and rough idle until warm. I will need to use the truck driving to Prescott next week, so I'll keep an extra gallon of coolant with me and top up when I get there.

 

[Karlsweg]

If it leaks into the cylinder enough, it could hydraulic the cylinder. End result, blown out cylinder wall/ bent connecting rod/ broken connecting rod. You say “hard start”. Do you mean turns over slow? If so the cylinder is filling with water.

 

[MikeT]

I know of an excellent Mopar shop in Prescott. Lots of mopar experience and knowledge. PM me if your interested. I'll give you their contact info and you can make arrangements in advance. I use them myself.

Mike

 

[Brando_SLT]

Appreciate the info guys. By hard start I mean it's rough idle for 10-15 seconds. It turns over and catches just fine.

@MikeT If I were going to be in Prescott for more than a couple days I would definitely take you up on that.

So something weird... When I put the system under vacuum it will hold at -20 in/hg forever, no bleed off. If there were a cylinder head/head gasket leak, wouldn't it bleed off pressure?

 

[Brando_SLT]

Double post.