Head gaskets???

[m67tang]

1990 IDI
Blows bubbles out coolant overflow. Runs low on coolant while driving. I pressure tested radiator, no serious leakage. I then pulled glow plugs and pressurized the radiator again. Nothing happened.

What am I missing?

 

[DrCharles]

Probably head gasket.
Your pressure tester might put 20 psi on the cooling system. Combustion pressure is far higher than that, by two orders of magnitude... and going in the other direction (cylinder to water jacket).

I had a turbo inline-six once that ran fine for hundreds of miles UNLESS I hit the gas hard enough to go into boost. Then it would puke the coolant and overheat within 30 seconds. Wait for cooldown, refill, drive for hours again, etc. Sure enough, fire ring in one cylinder was pushed out by detonation. Under moderate power it never leaked. And it never had oil in the coolant or vice versa.

 

[m67tang]

I’m agreeing that most likely head gasket. Gonna drive again and check it on the same trip. Been about 1 1/2 gallon each time on this particular trip.

 

[david85]

I second DrCharles

Foam at the expansion tank is 99% leaking a head gasket. IDIs are all iron, so they don't usually blow from one moment to the next like some of the newer pot-metal headed engines. Instead, they just slowly get weaker and leak worse until coolant loss and overheating force you to pull over.

However, even if you don't wait that long, damage can still occur on the mating surfaces of the head and block. I've seen this happen with my Dad's 6.5 turbo, and to a lesser degree, my own 6.9 turbo before it was studded. The 6.5 was repaired using a high temperature epoxy my dad found at NAPA. I would have never though something like that could last nearly 20 years but it did (and still holding). My 6.9 ended up with new heads that were already faced. The block did have some erosion but I was told by my machinist that it wasn't enough to worry about. Again, so far, so good.

Bottom line is that once you're confident it is in fact a leaking head gasket, its best to stop running it.

 

[G. Mann]

Start the engine, open the hood and remove the radiator cap, watch what the coolant does.

As the engine comes up to operating temp, if you have a head gasket leaking, the coolant will surge out the cap opening. If you reach over to the Injection Pump throttle arm and rev up the engine, coolant will "boil" out the cap opening. Low idle will give lower "boil" ... rev up the engine with cap off, the coolant surge out the cap opening will follow the revs, ie, faster revs, more surge...

If it does that, you need head gaskets.... bad.. don't drive it till you do..
it WILL blow out the coolant, overheat, cook the engine, warp the heads, etc etc etc...

The sooner you fix it, the less it will cost in new parts...

 

[m67tang]

Gotcha

 

[Macrobb]

In my '93, it took months to go from "bubbles in the overflow on shutdown after a long hot pull with a trailer" to "bubbles when running, cloud of white coolant smoke". It just finally gave out completely one day.
Replaced head gaskets, problem solved*
(*note: this motor is in my tan '88 after HG replacement)