overflow tank

[amaurer]

The overflow tank has always been a bit mysterious to me, so maybe this is normal but when in doubt, why not ask...

After running long and hot on the highway I parked the cruiser for maybe 30 minutes and then came back out to tinker. I was measuring some s*** on the alternator, so I was essentially starting it - idling for 2-3 minutes - and then shutting it off.

When I shut it off, for maybe 30 seconds the radiator was intermittently pushing bubbles into the overflow. bubble bubble.... bubble bubble.... bubble bubble.... etc

I can't really wrap my head around why it'd do that. Anyone know?

I've heard "head gasket" mentioned, but I replaced mine maybe 5 months ago. I also heard that HG failure produce lots of bubbles in the coolant itself, however mine is clear. Coolant also smells... great, honestly... am I the only one who likes the smell of coolant?

(Maybe its worth mentioning, maybe not - I have noticed that if I'm running hard, my coolant level (inside the rad cap) will appear to be low the next day. If I top it off, however, the rad will puke the coolant i added into the overflow. If all I'm doing to driving around town, the coolant level stays constant in the bottom of the filler neck)

 

[FJ40Jim]

Check the radiator cap & overflow hose. When the coolant "shrinks", the radiator should suck coolant back into the radiator from the overflow. Instead, it is sucking air back in somewhere, which leads to the coolant level going down after every heat cycle.

 

[lostmarbles]

Check the radiator cap & overflow hose. When the coolant "shrinks", the radiator should suck coolant back into the radiator from the overflow. Instead, it is sucking air back in somewhere, which leads to the coolant level going down after every heat cycle.

I agree.

I suspect air is getting into your radiator somehow - But the cap isn't my only "area of suspicion". ..... Perhaps you have a leak elsewhere that you haven't noticed?

I believe (same as FJ40Jim) that the radiator should always be full of coolant and should not normally contain any air.

However, if you removed your radiator cap recently for any reason, then you WILL have allowed air into the radiator. But if it is a small amount, the expansion and contraction of the coolant that occurs during subsequent successive warm-up/cool-down phases should result in that air being purged out (through the reservoir) and replaced by fresh coolant from your reservoir. (The expanding coolant will push bubbles of air into your coolant reservoir as your engine warms up. And then, when your engine next cools down, it will suck coolant back to replace that air. And the process continues on successive warm-up/cool-down phases till all the air you allowed inside has gone..... which can take about a week in my experience!)

So if you saw those bubbles AND HAVEN'T RECENTLY HAD YOUR RADIATOR CAP OFF then I too suspect a coolant leak somewhere near the top of your coolant system (from which the vacuum that occurs on cool-down is sucking in air).

If it is a headgasket leak that is letting air/fumes into your coolant then I think you'd notice oil and muck in your coolant.

Perhaps you should pressurise your coolant system and check for leaks Drew?



PS. As I'm sure you know - The best time to check the coolant level in your radiator is when the engine is cold. (To avoid coolant from spilling out as soon as you remove the cap.)

However, at this time there is a vacuum in your radiator (left over from it performing its task of "sucking coolant from the reservoir").

This means that the level of coolant in your radiator should always "fall slightly" the second you remove your radiator cap. ........ So make sure you don't confuse this "normal behaviour" will "having a leak present". Apart from anything else, the big radiator top&bottom hoses tend to suck-in slightly under vacuum and expand slightly (to hold a bit more fluid) when the cap is removed.

 

[Pin_Head]

Check for bubbles with the cap off and the engine running. That would be a more reliable sign of a bad head gasket or crack in the combustion chamber.

 

[bsevans]

If you are concerned about combustible gases in your coolant you can check that directly using kits like this one. I have this and it works.

Lisle Combustion Leak Detector

You can also get this at NAPA but you will pay more (P/N 700-1006)

 

[PabloCruise]

I encountered a situation with my 55 radiator that I will share...

My radiator will not recover coolant from the overflow reservoir upon cooling down. I discovered that the neck on my radiator (area where radiator cap seals) was damaged, there was material actually missing from the seat area. This damage prevented the vacuum that develops when the coolant temp lowers from recovering the coolant. Instead, that vacuum was pulling outside air in and leaving coolant in my overflow reservoir.

Not sure if that applies to this situation. Make sure your neck and radiator cap gasket are complete!

 

[amaurer]

My radiator and cap are brand new... well, less than a year old.

I ran the engine with the rad cap off - no bubbles. And no combustion smell. I think I'm OK on the head gasket front.

Poking around, I'm noticing that I've got a lot of moisture around the thermostat housing gasket. I have a new one on the way. I'm also noticing that, at times, there is a particular spot on the underside of the hood that seems to be damp or dirty. I've never been able to catch anything squirting, but its suspicious, so I have a new radiator hose set en route, and will swap all the heater hoses as well. Stay tuned.

 

[bsevans]

My radiator and cap are brand new... well, less than a year old.

I ran the engine with the rad cap off - no bubbles. And no combustion smell. I think I'm OK on the head gasket front.

Poking around, I'm noticing that I've got a lot of moisture around the thermostat housing gasket. I have a new one on the way. I'm also noticing that, at times, there is a particular spot on the underside of the hood that seems to be damp or dirty. I've never been able to catch anything squirting, but its suspicious, so I have a new radiator hose set en route, and will swap all the heater hoses as well. Stay tuned.

So you think since you cannot smell combustible gases you are good to go. Well, that would be a false assumption that you better hope is right. If in fact you have a coolant recovery tank that maintains enough fluid to cover the bottom of the tube in the recovery tank there is no source for air being pulled into the collant system that would not leave the tail tail signs of a leak. If your thermostat housing gasket is leaking you should see the signs of the leakage below the thermostat housing. When mine leaked you could follow the trail of antifreeze easily from the gasket down the engine. Both the upper and lower thermostat housings are prone to pitting and when that occurs a good silcone sealant is required on both sides of the gasket.

 

[amaurer]

So you think since you cannot smell combustible gases you are good to go. Well, that would be a false assumption that you better hope is right. If in fact you have a coolant recovery tank that maintains enough fluid to cover the bottom of the tube in the recovery tank there is no source for air being pulled into the collant system that would not leave the tail tail signs of a leak. If your thermostat housing gasket is leaking you should see the signs of the leakage below the thermostat housing. When mine leaked you could follow the trail of antifreeze easily from the gasket down the engine. Both the upper and lower thermostat housings are prone to pitting and when that occurs a good silcone sealant is required on both sides of the gasket.

You mean that *could* be a wrong assumption (as all assumptions might be). I know (from other threads) you think highly of that tester, so I'll keep it in mind, but at this point I think its premature. After all, I said I *do* see leaking from my Tstat housing...

 

[bsevans]

You mean that *could* be a wrong assumption (as all assumptions might be). I know (from other threads) you think highly of that tester, so I'll keep it in mind, but at this point I think its premature. After all, I said I *do* see leaking from my Tstat housing...

No, I said that the assumption that if you cannot smell combustible gases, means there are none is a false assumption, which it is.

 

[amaurer]

No, I said that the assumption that if you cannot smell combustible gases, means there are none is a false assumption, which it is.

Well, if you want to be pedantic, you actually said:

So you think since you cannot smell combustible gases you are good to go

Which only *might* be a false assumption.

But I'll tell it like it is - I don't want to spend money on a tester when there is no positive indication I need to. New head gasket and none of the other (if unreliable) symptoms of a HG failure does not say to me "go out and buy a special tool". Plus I'm cheap.

 

[amaurer]

Ok, I changed every soft hose in the system and replaced the leaky Tstat gasket (and added some sealant).

The verdict? Er, I dunno!

So, prior to doing all of this, any time I took the radiator cap off there would be a fair amount of vacuum in the radiator (when completely cool) and the cap would sorta pop off with some splashing of coolant.

Now there is no vacuum, and no splashing. Still no change in the coolant level, I won't know until a long roadtrip.

Honestly I can't imagine how what I did changed that - it would seem to be a cap problem but I'm using the same cap as I was previously, which itself is only about 5000 miles old.

Any thoughts?

 

[amaurer]

well, something is still amiss.

I went for a long drive and some wheeling today. Everything is fine (checked coolant level in the morning) until I parked on a steep downward slope and hopped out to check a line - I noticed coolant dripping all over the place.

I pulled the cap off the overflow (which was overflowing) and it was a constant stream of coolant coming out of the tube. I hurried through the obstacle to flat ground (maybe 3 minutes or 50 feet) and looked again - no dripping. After the wheeling but before the highway trip home the rad was down 0.5 gallons - which I topped off and am now home.

I'm confused.

 

[bsevans]

well, something is still amiss.

I went for a long drive and some wheeling today. Everything is fine (checked coolant level in the morning) until I parked on a steep downward slope and hopped out to check a line - I noticed coolant dripping all over the place.

I pulled the cap off the overflow (which was overflowing) and it was a constant stream of coolant coming out of the tube. I hurried through the obstacle to flat ground (maybe 3 minutes or 50 feet) and looked again - no dripping. After the wheeling but before the highway trip home the rad was down 0.5 gallons - which I topped off and am now home.

I'm confused.

Well, if your 40 was lower in the front than the back of the engine and had radiator fluid pushing out like that, I would be inclined to suspect a minor head gasket leak associated with cylinder #4, 5 or 6. No path for the combustion gases to escape without pushing volumes of coolant. When my head gasket finally blew it was pumping fluid so hard that it finally blew off the upper radiator hose. If it is a HG leak it may eventually tell you in no uncertain terms what's going on. Hopefully you won't be wheeling in Moab when it occurs. But hey, you're convinced that you do not have a head gasket leak so this is pure conjecture on my part.

 

[amaurer]

Well, if your 40 was lower in the front than the back of the engine and had radiator fluid pushing out like that, I would be inclined to suspect a minor head gasket leak associated with cylinder #4, 5 or 6. No path for the combustion gases to escape without pushing volumes of coolant. When my head gasket finally blew it was pumping fluid so hard that it finally blew off the upper radiator hose. If it is a HG leak it may eventually tell you in no uncertain terms what's going on. Hopefully you won't be wheeling in Moab when it occurs. But hey, you're convinced that you do not have a head gasket leak so this is pure conjecture on my part.

I'm buying your damn tester to be sure.

What will you do with yourself now?

 

[Rocky_LC]

It would seem to me that any head gasket leak would have the same effect ("hyper-pressurizing" the cooling system). If parked on a downhill slope, the coolant would be in the neck, and thus be forced out.

It really doesn't matter what cylinders are bad - the effect would be the same (eventually pulling the head).

Good Luck. Let us know what happens.

 

[amaurer]

just to update - the truck is now cold so I checked the coolant again - it didn't use ANY between the trail and my house which is about 1.5 hours of highway driving. whatever is doing this clearly only does so during trail driving and not highway... whatever the hell that means.

(I will point out, highway driving is a lot harder for a 3B than trail riding. i never break 600F EGTs on the trail, but I drove home today with a headwinds and pushed 1000F the whole way. i would have expected that to be harder on the coolant than the trail......?)

 

[amaurer]

combustion tester doesn't come till tomorrow, but I did find this and think its interesting:
JEEP: COOLANT BUBBLING WHEN PARKED DOWNHILL - AutosTalk Forums

specifically the bit about if an air bubble travels to a hot part of the engine when I'm parked downhill, it'll expand and force coolant out... hmmm. that would be consistent with the fact that I've only found coolant missing after offroading (hilly trails) or facing downhill, and that i don't use any on the highway. but then, i suppose an outward-only HG leak might do the same things. bah

 

[bsevans]

combustion tester doesn't come till tomorrow, but I did find this and think its interesting:
JEEP: COOLANT BUBBLING WHEN PARKED DOWNHILL - AutosTalk Forums

specifically the bit about if an air bubble travels to a hot part of the engine when I'm parked downhill, it'll expand and force coolant out... hmmm. that would be consistent with the fact that I've only found coolant missing after offroading (hilly trails) or facing downhill, and that i don't use any on the highway.

So are you sure that all the air has been purged out of the system? I installed this so I could fill the engine with coolant and remove all the air. I just remove the cap and fill till it comes out. I'm having a hard time buying that your system is some how pulling air into the coolant system when it is set up properly and all clamps have been properly tightened. There is a solution that you have not come upon - Yet.

 

[amaurer]

its the head gasket. it'd been bubbling much worse these last few days, so i'm not really surprised anymore, but the tester verifies it, kinda.

this tester seems to be wonky, or at least the diesel test fluid is.

First picture (red fluid) is the diesel test fluid. The right cup is new fluid, the middle cup is fluid that bubbles on the rad. for 20 minutes, and the left cup I bubbled with a line right form the tailpipe as a control. I can't see a significant change in ANY of them!

For s***s and giggles I did the same thing with the blue gasoline vehicle fluid and it changed to green/yellow from blue. Lord knows why they sell a special diesel fluid, but its clear that whatever is coming out of the radiator is not just air.