Coolant leak

[Locomoko]

New to the forum, I have a 98 6.5 TD Suburban that has been leaking coolant from some unkown location. After trying all the things I knew about I took it to a good diesel mechanic who pressure tested at the overflow reservior, and the pressure held at 27lbs for 15 minutes or longer, the engine was at operating temp. We fill the reservior about once a week. The cost of coolant has me putting in straight water at this point, which I cringe to do. I have removed the radiator & flushed the system once. The oil is still black. Both the mechanic and myself are stumped. Are there any ideas I could try?

Stumped

[Robyn]

Welcome to TDP

With the symptom you sre describing I am going to say a possible head gasket or even a cracked #8 cylinder wall.
The head gaskets can go on #2 and #7 and possibly #1 and #8

The #8 cylinder crack that can show up is at the top of the cylinder and looking at it from the RH side of the vehicle it would be at about 7 oclock looking down from the top.
The cylinders crack between two bolt bosses and the crack runs radially around the top of the cylinder.

These are a game over for the block if that is what it is.
The slow loss of coolant is a symptom of either of these failures.
The only real way to check is to yard the engine apart at this time.
A head gasket failure at any of the end cylinders will be quite obvious.
The cylinder crack will show as an etched spot in the lower rear quadrant of the top of the cylinder.
You might even have a cracked head.
These issues are not uncommon especially on a high miler.
The 98 block could very well see the cylinder cracks.

I would plan on ripping the little sucker out of the truck and get it on a stand so you can get a good look at the things.
Working in the engine bay is just plain nasty. Nuff said.
Also do check very well for a leaking soft plug or rear heat unit issue or ????????? before you tear the engine out. Not kewl to find a little leak in a hose or other issue after you spend the better part of a day tearing the engine out of the truck.
Keep us posted

Robyn

[bl78ljb]

Same problem I had in my 98 Suburban, and it ended up being a cracked block. The darn thing ran great too despite using more coolant than I could afford until it lost all of it into the crank case on a -10F winter day on I95! I wouldn't let this go on too long before looking into it. BTW where are you located, so other could offer advice for mechanics etc if you don't already have a good diesel mechanic?

[Locomoko]

OK, but how does the coolant leak inside a cracked block without turning the oil brown, etc.? Wouldn't the type of leak you are describing be in the top end and wouldn't I be loosing compression? Appreciate the responses...

still looking

[bl78ljb]

Robyn or someone may be better at explaining this than I, but from what I understand some of the coolant may be blown out the overflow by pressurizing the system (don't think that accounted for much of mine), and some of it is burnt by the engine and I didn't notice that the exhaust looked differently but after the new engine I realized that it had a fine white smoke prior and seemed to be more volume likely due to the steam. I also noticed that after the engine finally failed the coolant was being sucked into the turbo and if the head has the leak, especially on the right it may just be sucked into the turbo and act as a water cooling system and take out the turbo bearings in the process (my turbo was shot in the end, more endplay than I thought possible:eek:). Right up until my ultimate engine failure I had no visible water in the oil no brown no separation or water droplets on the dipstick, very different from the gassers I am used to working on.

[tommac95]

The vehicle's climate of operation , mileage/service accumulated , etc are helpful info. Sometimes seasonal temp swings cause small coolant leaks at various spots. The quantity in your case is excessive, though.

If the ratio of coolant/water (mixture) has too much water , you get good heat exchange efficiency , but risk blowing out hoses/exchangers, as the cooling jacket pressure skyrockets !!

[rustyk]

I agree with Robyn's assessment - the OEM engine in my motorhome showed a need for adding coolant. What was happening was that a bad head gasket was allowing pressure to build and blow coolant out through the reservoir overflow.

Bring the engine up to operating temp, and watch the coolant reservoir for bubbles.

[Locomoko]

Ughh! this is depressing, I can see $$$ flowing out like Niagara Falls, with diesel fuel skyrocketing, its time to stop the bleeding!

frustrated... thanks for the advise, Aloha!

[raypete]

I had the same problem w/my 1999 Suburban. Turned out to be a crack in #3 cyl. wall. Now have Jasper which is running good.

[tuckerman]

My block heater is leaking on my 97'. Its just in front of the oil filter. Thats tomorrows job.