87 300d #14 head
 

HI. My car is a 87 300d with the #14 Head.
I've put 13,000 miles on it since I bought it. Changed the oil from dino to 15w-50 mobile 1. Maybe used a qt in 5,000 miles. I also put a new thermostat and flushed the coolant system because I wasn't getting any heat. Didn't fix it but a new radiator cap did. Now anytime I open the coolant tank cap there is a "sshhh" of pressure releasing. I don't lose any noticeable amount of coolant. I did not lose any in the last 2,000 miles.

I know if the top radiator hose is hard in the morning that can be a sign of a cracked head. My top hose isn't really hard. I can squeeze the top hose sides together. **But if I open the cap on the coolant tank it goes SSHH and realease some pressure. Is this an early sign of the head being cracked?

Example: I drove it about 11 hrs straight on Friday. Got home turned it off at 10pm and at 8am it had a little sshhh of pressure released in the morning with temps staying around 45-50 degrees all night and day.

I drove it for 6 straight hrs saturday - got home at 5 and this morning it was slightly leaking a little coolant from the top radiator hose at the radiator. The temps dropped around here from 45 yesterday to the low 20's.

Thanks in advance and sorry for the long post

It sounds like you have a breach of combustion pressure into the cooling system. Unfortunately with these cars, that usually means cylinder head cracks rather than 'just' a head gasket failure. Leaks from cooling system hoses and fittings indicate of high residual pressure in the cooling system. The more pressure you lose, the less stiff the hoses will be. You might buy time by leaving the radiator cap loose such as on the first catch. This will prevent build-up of pressure but severely reduces the ability of the cooling system to dissipate engine heat. Hopefully that's not a problem this time of year in the US. Check the coolant level every time before you start the engine if you can and keep one eye glued to the temp gauge.

IIRC Mobil 1 15W-50 is not a Diesel rated oil. Get Mobil 1 turbodiesel/truck 5W-40 (5W-40 Diesel Engine Oil | Mobil 1™ Turbo Diesel Truck) if you must stick with Mobil 1 but get a Diesel rated oil.

Sixto
87 300D

I think the system should have no residual pressure or even a little negative pressure after sitting for eight hours. Any assessment must be made with a known tight cooling system. I was thinking you may have a very small crack yet and have no ideal if it will worsen. Then maybe not. Are you certain the cold whoosh is outward?

My 87 with #14 head has been doing the exact same thing for the last 18k miles since I bought it. Its fine, just keep driving it. It might get worse some day or it might not but as long as you're not mixing fluids or losing coolant you're fine. I'm a bit paranoid so I have a spare #17 cyl head and all the gaskets ready to go in should the need arise. I also installed a colder thermostat, more powerful electric cooling fans triggered at a lower pressure and lower pressure coolant cap. I don't want this engine over heating under any circumstance. I would rather shut off the engine than ever see the temp gauge go over 100c, fortunately its never come to that.

Your rate of oil consumption is normal. I would stick with a diesel rated oil instead of the M1.