1999 D1 SD, 4.0/auto

Ever since I put a new thermostat in my Rover it's been intermittently spiking the temp gauge every so often. It'll get hot, I pull over and it comes right back down. When I open the hood to have a look around though, there's no evidence of overheating. No smell, no steam, no excessive pressure. If I sit and watch it long enough you can see the coolant rush the bottle and bubble around, and then go back down to level.

At first I thought the new thermostat was bad, so I put a new OE unit in. Same issue. It ran in the 170*s for what I'm going to guess was probably years with the old thermostat stuck wide open.

After many rounds of bleeding the system and experiencing the same thing I took it to the shop to have the system vacuum bled. The system won't hold a vacuum. They said there's no combustion gases entering the system (my guess is they used a block tester kit, I also checked it with my kit, and saw no evidence of exhaust gases), they said their guess is slipped liners causing this problem. I don't see how that's possible, but I'm open to opinions.

Right now I'm leaning towards yanking the thermostat out and dealing with the rich mixture situation, or just driving it until it pops.

I have an ultragauge that I watch, the fan clutch is working, the "overheating" situation doesn't seem to be isolated to any particular driving situations. I'm not getting any milkshake in the oil, or coolant system. The coolant hoses, expansion tank, and cap are new.

I'm stumped. The system either has air in it, or is sucking air in from somewhere else while running. There are no leaks, no coolant loss, no coolant gained, no oil consumption, no signs of anything out of the ordinary, except air in the cooling system.

 

My symptoms exactly match this poor guy's. I'm going to swap the hoses on the heater core and see what happens.

https://landroverforums.com/forum/di...l-46615/page6/

 

I'd like to know how the came to that conclusion, as 3.5/3.9/4.0/4.2's were not really known for liner problems unless you totally cooked it time and time again. Does it have a knock/tick once it warms up?? Tearing it apart and looking at the HG would tell you if you had any liners slipping as they'd be beat to hell from the liner constantly hitting it. For the coolant system not holding a vacuum you have so many places for a leak. Throttle Body Heater Plate (kinda rare on a 3.5/3.9/4.0/4.2, but it is still a gasket), radiator, heater core, expansion tank, cap, and every single hose and hose clamp connection. Honestly just sounds like air in the system to me or a temp sensor that's gone funky.

 

My '99 D1 has been doing this for about a year now, only does it when I start it cold, and then after about 15-20 min, the gauge pegs and then goes down to normal temp. Scanner follows it with the temp readout. Once it does it's dance, it is fine for the rest of the day. I have replaced just about everything and bled it numerous times. new cap, new hoses, new thermostat, 180 and 195 versions,new clutch fan. 2 new electric fans, nothing changes I just live with it now. put 11,000 miles on it and it still does this occasionally.

my thinking is it cannot get hot that quickly, then cool off just as fast. it pegs, then goes to normal in 5-10 seconds. physics says it can't do that

Seems like if you let up on the gas, it goes down quicker.

 

No ticking, and I'm 100% in agreement with you.

These are my thoughts as well.

 

One low cost item ($20) to make sure you are getting accurate info is the coolant temp sensor.
https://www.roverparts.com/instruments/sensors/ETC8496/

I does sound like you are getting air into the system. The fact that you are not losing coolant is a good sign.

 

Have you tested the sensors to make sure its not a bad sensor?

When it is overheating, are the hoses rock solid?

It probably won't hold because you have a bad hose/connection somewhere, I have one on the intake that has been hanging out for a year.

 

I've been meaning to get a new sensor,sensoI'm not really getting any indication that it's bad. For $20, I'll probably just go for it one of these days.

I'm gonna double check the hose connections this week when I swap the hoses on the heater core.

The hoses aren't rock solid when it's overheating, and they don't even feel overly hot. I'm confident that it's not really overheating, but the coolant rushing into the bottle, and "waterfall" sound behind the dash makes me believe that there's just trapped air. It is a bit troublesome that it didn't correct itself with the vacuum fill, though.

I have lots of things to try, but I feel better about driving it in the meantime.

 

I've never had luck with the vac fill.
I've always just raised the front of the truck really high and bled that way.

A bad heater core will pull in a bit of air.

 

I'm not getting any coolant on the carpet, or smells with the heat on. I guess at this point a reverse leak sounds entirely possible.