1995 Defender 110 - 300 TDI - Overheating at Highway Speeds

[Nmgoes]

My D110 with a 300 TDI started overheating at highway speeds recently. Driving around in town (under 50 mph) and not under a load- she runs cool. But if I'm putting load on the engine or running at highway speeds, the temp spikes FAST.

Any suggestions on what may be causing this?

I checked my antifreeze/coolant expansion tank and have plenty of fluid. No leaks in the radiator.

Any suggestions are much appreciated!

 

[javelinadave]

As a general rule 300Tdi engines run cool. It isn't uncommon for people to remove their cooling fan in cooler climates to get the engine up to operating temp. Sounds like either the thermostat isn't opening, your radiator is obstructed internally or your timing is way off.
My guess is you need a new t-stat. I have had perfect luck with this:
Amazon Link
You will need to reuse your old rubber gasket and clip off the little brass vent. I have had mixed results with the blue or the green box t-stats.

 

[Z.G]

Sounds like the radiator is blocked or clogged.

 

[Napalm00]

i agree with both, id replace the tstat anyway AND run some evaporust thermocure. I used to do this whole thing for cleaning rads, this stuff works great

 

[Nmgoes]

Thanks guys, for the tips. I'll try it out.

 

[Nmgoes]

i agree with both, id replace the tstat anyway AND run some evaporust thermocure. I used to do this whole thing for cleaning rads, this stuff works great

Dumb question (first Land Rover), but would the Evaporust Thermocure go into the expansion (overflow) tank?

 

[UnfrozenCaveman]

... run some evaporust thermocure. I used to do this whole thing for cleaning rads, this stuff works great

Wow, learn something new every day around here. I didn't know about that stuff. Thanks Napalm ... two words I'd not normally associate

 

[Napalm00]

Dumb question (first Land Rover), but would the Evaporust Thermocure go into the expansion (overflow) tank?

Explicit instructions on the bottle. You're going to need some empty space because you're going to be flushing tons of water in and out of that motor. I emptied the coolant fully flushed it with a garden hose and caught all that water recycle all that stuff then filled it up with thermocure and water and then drove it around for a week.Flushed out a couple of times with clean water nice and hot full all the way burp the system ect. Came out looking beautiful

I recently did this on a 1964 dart as well and it came out absolutely perfect.

I actually have a whole post here on this forum about how to flush your coolant using all sorts of chemicals you can buy on Amazon. I totally changed direction this is much easier

 

[RBBailey]

I would check the actual temps with an IR thermometer at multiple spots on the radiator, engine, hoses, thermostat housing, etc., just to make sure you are not getting erroneous readings before putting work into it.

When I cross reference my VDO gauge with what I see at the sender, housing, hoses, and other spots, it is as close as can be determined by looking at the VDO vs. the digital read-out. If I were to see a temp of 180 degrees on the VDO, I will see 179 on the IR digital read-out at the sender. I check often.

 

[jymmiejamz]

FWIW, I had a thermostat on my old 110 start to stick closed. It just gradually ran hotter on the highway. I had already replaced the radiator a year before.