This is a bit random,but there was a lot of traffic at the dump and it popped into my head.

The reason we see better and more consistent temps with the mod its the thermostat will tend to be open longer and more often. The reason of course is that the hottest water from the engine is hitting thermostat. It is also how the engine was designed, and everything up our Disco II's basically ran an inline thermostat.

On the stock BMW setup the thermostat is receiving coolant that has already been partly cooled resulting in less and shorter open times.

I wonder if this could be part of the cause of the head gasket issue in the D2's

 

I definitely believe the factory thermostat was a huge contributor to the HG issues, probably cause 75% plus of the issues. On my trip down to SC there was a Disco on the side of the interstate with steam rolling out of the hood. I swung around and pulled over to help. College kid who had inherited the truck from his brother. Had the factory thermostat, which was old and brittle. The top hose barb had basically disintegrated and the hose popped off, no doubt due to an overpressure condition caused by blown hg, but still had him on the side of the road.

 

All sorts of things contribute to a Bosch 4.0/4.6 having HG issues. From clogged cooling systems due to Dexcool, Throttle Body Heater plates slowly bleeding the coolant out until it hits a critically low level (usually to late when the red light illuminates on the dash), original thermostats that have NEVER been changed out and they're stuck closed or full of debris from Dexcool, poor maintenance, someone that overheated it several times until finally a sleeve slips, or worse yet corrosion caused from mixed coolant eating it's way thru a cooling jacket and to a sleeve = engine is TOAST.

I owned 2 03 D2's fresh off the showroom floor, and I put 159-189K on both of them while I owned them. I never did a single HG job on either one of them. This was way before OBD2 scangauge/ultragauge's so god knows what my engine temps were! We all went by the gauges back then. No one had ever heard of putting the 180F thermostat out of a TD5 into the 4.0/4.6, no Hayden 2991's or Dorman 620-112 fan blades either. My only issues which happened to each of them = P0441 faults due to purge control valves (hyundai part fixed that), OEM spark plug wires biting the dust, and seepy valve cover gaskets (way before my FV308 PCV Upgrade). Either one never gave me any cooling issue problems and I owned them for nearly 6 years.

These days you hear and see D2/P38's with blown HG's due to age, and poor maintenance from previous owners IMHO. Heck on my last visit to Austin Roverworks I saw plenty of LR3/RRS/LR4's sitting there with HG issues waiting to be fixed or priced out. It was pretty much 50/50 between RRC/D90/D110/D1/D2/P38 & LR3/RRS/LR4. Main reason = age & maintenance. The LR3/RRS/LR4 has a plastic thermostat housing assembly and with age they're known to crack/leak & that's not even counting the plastic bleed T which is also known to just crumble. Either of those goes un detected and bingo it's in the same boat as any RRC/D90/D110/D1/D2/P38 with blown HG or damaged blocks. I see plenty of LR3/RRS on CL with blown HG, or dead engines. A buddy of mine got a flawless looking 08 Supercharged full size RR with a blown 4.2L due to the thermostat housing leaking for 1,500.00. The previous owner got a price quote from a LR dealership and just sold it ASAP for parts basically with a clean title. My friend is dropping in a 4.2L with a warranty and he'll have a great LR for next to nothing.

I just always do a pre-flight check before driving off and it's paid off with all my LR's.

 

@Best4x4 yea we had a SC RR here too same blown head gasket , tried to buy it at 500.00 he would not sell still sittin g2 years later and just rotten on the inside with mildew.

And thanks for the feedback

 

No problem! The other issues with HG can also be from someone not following the proper torque specs/sequence when tightening the bolts leading to an early failure.

 

I am actually a fan of the bypass thermostat. I have had them on my BMWs and Fiat 124s (original, not the new model) and the beauty of them is that the coolant is always circulating. This keeps hot spots from forming in the head as the water gets to or above the boiling limit before the thermostat opens. With the Coolant always flowing past the head, the engine and coolant heat more evenly until the thermostat slowly opens, letting cool (or cold in winter!) coolant into the engine to gently ease it into a more open loop through the radiator.

 

When I got my disco with the oem thermostat it was running 210-230. That’s pretty hot. Also pressure dramatically goes up at 230 vs 195.
I’m still loving my inline thermostat mod
bought it the day my 180 thermostat failed closed and temps shot up to 230. Ultraguage began beeping at me at 215

 

The big problem with the OEM thermo is that it is so far away from the motor. You have to warm up the water between the block and the thermo before it opens and there is no circulation. Worst design ever.

Inline 180 mod is the first thing I do when I get one.

 

183-190 in and out of traffic all day with the in-line t-stat.

 

I like the way that looks. Which aluminum T is that?