96 Disco 1 - intermittent "almost" overheating

bsa_m21 · Jul 8, 2017

So I was on vacation this past week in my till now, trusty D1. She only has a bit under 100k miles on her. Although we were only doing 80-90kph (50-60mph) fairly steady on back country highways, intermittently the temp would suddenly rise almost to the top of the "OK" scale. I would put on the A/C fans with little impact until I turned up the heater temp. It would then drop back to 1/2 way (normal) on the gauge. I could then turn off the heater and A/C and she would be fine again for an extended period, then it would repeat. At high speed (over 100kph+) she doesn't seem to do this.

So far there is no coolant loss and the system is not over-pressurized, no plugs are washed and oil is clean (just changed last week before heading out). I noticed yesterday that at low speed under load (going up a steep hill on my way home), the temp started to climb quickly, but I was close to home and turned her off (with the A/C fans running on) before it got too high.

I've now done the following with no change to this behavior, so far:
- separated the A/C and engine rads and cleaned between them and blew out the vanes in both rads.
- replaced the thermostat with a 180F, with the bleed hole at the top.
- flushed and replaced the coolant
- burped the system, twice

I was wondering if it might be the viscus fan, but that doesn't seem to fit what is occurring to my truck. I'm kinda hoping I don't need a new rad, re-core or water pump.

Any suggestions as to what to try next would be appreciated.

Regards,
M.

4Runner · Jul 8, 2017

When my Rover acted that way it was a plugged radiator. If you unplug your AC compressor, your AC fans will be more effective at cooling things down because you will have no extra heat load from your AC condenser when you turn your AC on. That's just a temp/ oh shit/ troubleshooting solution. Is your serpentine belt and tensioner in good shape? I think 100k out of a water pump on a Rover is about at the end but maybe someone could correct me on that. Good luck.

p m · Jul 8, 2017

M., you have answered your own question. If turning on the heat cools the engine off, you need to rod/recore/replace the radiator.

discostew · Jul 9, 2017

Your radiator is probaly rotting. look at the back side of the radiator and see if all the cooling fins are intact. They seem to go away and only the core tubes might be what you have.

At speeds over 25 mph you don't need a fan, just the air coming thru should cool it.

bsa_m21 · Jul 10, 2017

I bit the bullet and ordered a new Rad and viscous fan coupling. Hopefully they will solve the issues.

forcefed44 · Jul 13, 2017

I'm following this thread. Post how this turns out. I have just had this same situation happen to me.. she never overheated or ran hot. Always stayed in the middle or slightly under the middle mark. It's just stiflingly hot outside so I put the A/C on and drove as normal. The temp was fine and after stop and go, the emp started to ride 1/16 off the middle mark. Got out to check, and temp went close to the 3/4 mark but never touched it. Electric fans are running efficiently. Decided to put the heat on and the temp went down quickly to normal. Drove around with A/C off and temp actually went lower that the middle which is normal for me. So I decided to put the A/C back on, drove a bit more and the temp needle started to creep slowly back past the middle. If it is the radiator, I'll do the same and order one up, I already have new clutch fan in box in the cargo area.

'95 D1 3.9
Full tune up
Coolant flush, burped, new water pump

squirt · Jul 13, 2017

forcefed44 said:
I'm following this thread. Post how this turns out. I have just had this same situation happen to me.. she never overheated or ran hot. Always stayed in the middle or slightly under the middle mark. It's just stiflingly hot outside so I put the A/C on and drove as normal. The temp was fine and after stop and go, the emp started to ride 1/16 off the middle mark. Got out to check, and temp went close to the 3/4 mark but never touched it. Electric fans are running efficiently. Decided to put the heat on and the temp went down quickly to normal. Drove around with A/C off and temp actually went lower that the middle which is normal for me. So I decided to put the A/C back on, drove a bit more and the temp needle started to creep slowly back past the middle. If it is the radiator, I'll do the same and order one up, I already have new clutch fan in box in the cargo area.

'95 D1 3.9
Full tune up
Coolant flush, burped, new water pump

Odd that the A/C would have that much impact. I guess if your radiator is just barely sufficient, the addition of hot condenser air blowing through it might push it over the edge. It would be more of an outside chance (though not unheard of) that the electric A/C fan on the condenser has been installed/wired backwards, causing it to pull air from the engine bay and counteract the mechanical fan instead of working with it.

bsa_m21 · Jul 13, 2017

If the temp drops when you put the heater on, I would think the flow in your rad is definitely restricted.

Last thing I did before I pulled the rad was to drive around with my trust OBD blue tooth and Torque Pro set to the temp screen. With the truck's gauge a bit below the 1/2 way mark, Torque Pro showed she was running at a steady 226F! The gauge didn't start to climb until about 234F and suddenly jumped to the upper mark at around 239F.

Parts should be here tomorrow. I have a separate mechanical temp gauge that I'm going to plumb into the system and mount on the dash, so I can see what she is really running at, at any given time.

Will post results afterwards.

As many have said before, these engines really do not like being overheated....

M.

4Runner · Jul 14, 2017

That is true. Your temp gauge is more of a panic gauge. Use a different method for getting your coolant temps.

bsa_m21 · Jul 15, 2017

New Rad is in, plumbed, burped and comfortable. About 26C today (80F) and I drove her hard. Running nice and cool. Steady 195 - 205 all day.

Yay!! :bigok:

Search

96 Disco 1 - intermittent "almost" overheating

bsa_m21

Well-known member

4Runner

Well-known member

p m

Administrator

discostew

Well-known member

bsa_m21

Well-known member

forcefed44

Well-known member

squirt

Well-known member

bsa_m21

Well-known member

4Runner

Well-known member

bsa_m21

Well-known member