I have rad fluid returning into heads when I shut engine down and blowing out exhaust upon start-up.New lower hose cured problem for a day but issue has returned. What could be the cause? Bad rad ? Water pump ? Engine never overheats. Was parked for day and a half recently and this morn I had to add approx 1/3 L of fluid to top off rad.Took approx 6 kms to burn excess smoke away, then normal exhaust flow. Info would be appreciated.

 

There are only two ways coolant can get into cylinder to be burned off.

Most unlikely is the lower intake gasket leaking coolant into cylinder #1 or #6, coolant flows thru the lower intake from one head to the other on a V engine.
This would usually show up with coolant in the oil as well.
So remove #1 and # 6 spark plugs and see if either looks like it is getting steam cleaned, i.e. coolant burning in that cylinder.


Second, and most likely, is a cracked head or head gasket leak.
4.0l OHV engines have that cracked head cross to bare, head cracks between valve seats because of weak casting, small hair line crack at first, but when it does over heat it will get bigger.
Do a search here for "glove test"
It is a free test for cylinder to cooling system leak.

No, there doesn't have to be overheating at first, but there will be if you don't keep topping up coolant.
What happens is the leak will pressurized the cooling system more than normal so you will see overflow tank fuller than it should be.
And the amount of coolant getting into cylinder while running is almost none since head will have mostly air around the crack.
But when you shut off the engine the cooling system still has pressure in it and this will push coolant into the cylinder which now has 0 pressure, it will vaporize at first because of heat, but eventually it will remain in fluid form, and sit in cylinder until you start engine again, then you get the big smoke show.


Either of these can can hydro-lock cylinder, which can bend a rod or break a piston.


As said my money would be on a cracked head, hope it is just an intake gasket but that is a real longshot.

 

RonD. Thank you for info. Helpful and truck is in shop torn down to head gasket at this moment. Will post how it turns out in a couple of days. HOOKER

 

Two wks ago I wrote of having coolant blowing out exhaust on start-up. Have completed replacing lower head gasket and up from there. truck seemed to be cured on early short trips but after driving a 200 km run, after shutting engine down, smoke resumed on start-up again until burned off. Mechanic stated, no crack in block. Back pressure on shut down is forcing fluids by clamp on lower rad hose and excessive amount out overflow. What to do now ? Water pump, rad itself, rad fittings ? Rad pressure check was ok, but not tested immediately after shut down (whether there's a difference I don't know). Engine is strong, all rods were replaced as a couple were oblonged. This did eliminate a tingling when engine geared down to power up. Any suggestions/info would help. Rad was not flushed but was removed and coolant changed a couple of times. Truck has never overheated and still does not. Ran 500 kms to get home and she purrs on the highway. Once home and shut down, problem. Also, if block was cracked, is there a certain area cracks occur ? Not positive, but I think my mech simpy looked between cylinders and did not see a crack.....Should mention that head gasket installation went extremely well. Did eliminate air conditioning system (no freon?, never worked). Short trips after gasket work there was slight evidence of smoke on start-up but was minimal and dissipated quickly. Attributed this to cold weather and hoped was not an issue. Did not remove water pump from engine during gasket job.

 

Full over flow tank reads like cylinder leak.

Did you have the heads surface and pressure checked?

4.0l heads are known to crack between valve seats, it is a weak point in the casting, can be seen if inspected closely but can be missed if not looking closely.

I would do a Glove test(as mentioned above) to determine if it is a cylinder leak and then which cylinder is leaking, so there is no doubt on the next tear down.

Glove test
Cold engine
Disconnect coil connector, you want a No Start
Remove rad cap and overflow hose
Place latex glove over rad cap opening and use a rubber band to seal it to rad, or you can use a balloon or even a condom in place of the glove.

Block the overflow outlet with a vacuum cap or hose with bolt in it.
Cooling system should now be sealed.

Crank engine
Watch Glove
If it bounces(starts to inflate) then you do have a cylinder leak, period
If it doesn't then you don't

If it does you can find the leaking cylinder by removing one spark plug at a time and cranking engine each time.
When glove stops bouncing the last spark plug removed was from the leaking cylinder.
Put spark plug back in and crank engine to confirm.

 

Thanks again RonD. Will get back at it and inform later.

Hooker