I've replaced one coolant tank on my D2 (150k miles) when I replaced for the (seemingly knock off) 180 degree t-stat from Lucky 8. The tank ruptured after about 1 month; it formed very very small cracks in the top cover, and one considerable crack in the lower portion thats always submerged with coolant. I scoffed and figured it the hot-as-hell conditions here in GA in the summertime, or more likely, that it's a defective part.

So I purchased another coolant tank, and about a month later, more cracks show up and I'm losing coolant at a good rate. Something is very wrong with the cooling system.

I put in yet another coolant tank just a few days ago, had to drive a pretty big distance that day, and when I arrived back at the stead, coolant started to flow out of the overflow tube.

Points to consider:
-3rd coolant tank (Britpart)
-2 mo old reservoir cap
-new lines and hoses
-new Lucky 8 t-stat (180 degree)
-Original Nissens rad
-No apparent milkshake effect in the oil
-Using Prestone 50/50, no Dexcool
-Hot as hell outside, and running front and rear ACs (for the pup)

It seems like the cooling system is just getting overpressurized to the point where it's cracking these coolant tanks, and overflowing after long drives. I'm confident that it's not overfilled, but I suppose a good draining and refill might be fortuitous.

Using an Ultragauge, temperatures are between 188-195 for city driving, 199-210 on hwy. When coolant is at the appropriate level, the heater puts out heat, and I don't hear any waterfall effect behind the passenger dash. The engine temp does climb a bit faster now in these last few months than previously. If I'm carrying up a hill for instance, itll read 188 and a 1/4 mile of uphill later, we'll be at 197.

Any and all recommendations would be greatly appreciated, as it is summertime, and I would hate to overheat this old block.

Thanks,
Taylor

 

Sounds like it's time for a pressure test. Then upgrade to @abran aluminum reservoir tank.

 

I recommend running with the cap loosened one turn so it does not build pressure. Nothing good comes from having the cooling system pressurized.

 

Does the cap not provide a pressure release at a certain psi ?

 

You should NOT drive with a loose cap.


Your system is designed to operate within a certain pressure rating for multiple reasons. One being, at high pressure, fluid is harder to boil. If you lower the pressure thresh hold of the system, you allow the system to boil over, as well as expand and push out the emergency overflow.


If a car is needing to have the cap loose to operate, there is a problem with the cap...

 

I remember disco mike always saying to change your coolant cap on a major maintenance

 

Truth

Pressure lowers the boiling point of the fluid in the system. This pressure also turns to vacuum when the radiator cools off and sucks coolant back in. If you are pressurising the system enough to blow out the coolant bottle there is something else going on

 

I went through three expansion tanks from lucky 8 also and every couple months they could crack at the seam or develop little pin holes. The guys at Lucky 8 said they have been having this problem with the tanks and were going to stop selling them. I bought the aluminum expansion tank with sight window from carrs4x4 and no issues at all! Allisport sells a similar one but they were having an issue with the sight glass leaking so I stayed away from it.

It is a little pricy but worth the piece of mind that I won’t have it bust while driving down the road and toast my $2k complete rebuild.

Below is the kit with the radiator hose “T” to replace the plastic one that always fails and the expansion tank. You can get it without the “T” for $25 cheaper.


Aluminum Expansion Tank and Bleeder T for Discovery II Land Rover https://www.amazon.com/dp/B07N4D9M47/ref=cm_sw_r_cp_api_i_sstlDbEAGPGVM

above is the link to the amazon listing with free shipping.

P.S... never drive with your expansion cap loosened....

 

I wonder with these aluminum tanks if your having issues with pressure that tank ain’t gonna blow but something else will and it may be worst

 

Maybe they are defective tanks. That would be good news for the OP