Thread: 1988 Range Rover Overheating

My 84's overheating was due to most of the radiator cores blocked internally. Coolant still flowed across but not nearly enough to keep the engine cool in summer. The tanks were removed and the tubes cleaned then the tanks refitted.

Originally Posted by Graeme

My 84's overheating was due to most of the radiator cores blocked internally. Coolant still flowed across but not nearly enough to keep the engine cool in summer. The tanks were removed and the tubes cleaned then the tanks refitted.

Yep...that's what I was thinking.......along with a tired cooling fan viscous hub. The two issues combined to cook my 94 3.9.

Did you flush the radiator or did a radiator shop flush it? Did you reverse flush the system? Who installed the new water pump and thermostat? It sounds like you've either got a air lock or you need to get the radiator cleaned/rodded properly. Do you have a 50/50 mix of coolant/water? When the motor is at running temperature can you stop the viscous fan with a rolled up newspaper?

I'd think a viscous clutch failure firstly, otherwise a blockage in the radiator core.

I flushed and reverse flushed the radiator and block, and ran quite a bit of cleaner through the system. I installed the water pump and thermostat, done heaps of them on various cars. There is no coolant in the system.
At what speed does the air flow through the radiator become more than the viscous fan is pulling, since at idle I don't have a problem but at high speed I do? If it is an air lock how do I remove it?

What's the fuel pressure like? If it doesn't have enough or the right amount, the engine will lean out, causing the engine to heat up.

Seems like your cooling package is in good shape and this is another way the temp could be influenced.

I run the Range Rover on LPG with a BLOS mixer. There is an AEM Air/Fuel mixture gauge in the car with a wideband sensor I use to tune it, so I know the mixtures are good. I have gone a purchased a 4 core radiator, wait for it to arrive and I will see if that fixes it.

Originally Posted by Richard Kaye

I flushed and reverse flushed the radiator and block, and ran quite a bit of cleaner through the system.

This doesn't usually unclog blocked radiator tubes. Only the top few of mine weren't totally blocked yet it appeared that coolant was flowing.

It would actually be helpful to clarify the exact details, as leaving out something as seemingly inocuous as running on LPG can have a significant bearing on determining the cause.

Not only that, but some of the anecdotal evidence presented in the initial post does not influence the outcome and can actually cause a false diagnostic process.

So let's get down to brass tacks.

1. Flushing.

This is something you are supposed to do every 2 years, with a complete cooling system service. That is, inspection of all hoses for softness, abrasion, clamp tension, inspect all alloy fittings and steel fittings for corrosion and scale. Replacement of the thermostat if the system temperature is erratic during normal operation. Flushing BEFORE any system component replacement, such as new radiator or water pump or thermostat neck or heater lines is the best preventative to ensure the system is at it's best possible useable condition before the installation of new/replacement parts.

Flushing (correct procedure) is done with the thermostat removed, and the coolant completely drained and reverse flushed out with a hose until clear, the same process with the radiator.
THEN the actual flushing process takes place with a 15% citric acid solution by volume in the cooling system, bring the vehicle to operating temperature for a minimum of 15-30 minutes at a proper operating temperature. The solution must circulate for the entire period and the vehicle must be at operating temperature. The engine stopped when the period completes, and the block is again completely flushed clear with fresh water and the same for the radiator.
If you need to work out how to make a solution: https://www.rpc-rabrenco.com/assets/...s/Dilution.pdf will have you covered.

From there, a new thermostat can be fitted, as well as any new hoses/clamps/housing/water pump etc as is needed. Fill with the correct coolant solution and the system burped and brought to operating temperature again, to ensure all work carried out is tested functional and free of issue.

2. Fitting an auxillary temperature gauge. (good idea)

There are two places to install a reliable auxillary gauge, which will ensure the system reads reliably. One is in the inlet manifold behind the thermostat (on the top of the manifold, requires drilling and tapping) the second is in the radiator itself. These are the most stable measuring locations with a minimum of hysteresis. inline or fin mounted solutions have a greater hysteresis and the resulting gauge fluctuation can lead to a false belief there is a problem, where there isn't.

3. Temp gun readings (good test indicator, if done in the right spot)

Always measure on the rear of the hot side of the radiator as close to the inlet as possible, where there is the least amount of heat soak. Then measure directly on the thermostat housing, and lastly on the bottom hose outlet on the radiator. There should be very little difference between the thermostat housing and the radiator inlet, and about a 30 degree drop at the return.

4. Stationary idle versus low rpm low speed, low rpm high speed, high rpm low speed and high rpm high speed.

This is where people seem to come undone. Perhaps it is the belief that when idling, the issue of heat soak is not prevalent, therefore the radiator must be fine.

The truth is in clearly defined observation.

Idle and stationary - the engine should not even budge much above the thermostat opening . if the engine gets to 95ºC stationary, you might want to check your viscous hub and your plastic fan for signs of impending doom. If in doubt, replace. Don't second guess it, or it will cost you a shedload of cash to remedy.
If you rev your vehicle, then it's even more important to closely scrutinize the fan and the viscous hub for any potential crack propogation sites or axial/radial runout.

The next significant influencing factor is engine rpm. because the viscous hub reacts to temperature change, it automatically knows when it needs to "lock up" and drive the fan at pulley speeds. This is the temperature sensitive bimetallic spring action. the fan pulls the hot air through the radiator over the viscous hub and when that air is hot enough, the spring will bend and lock the clutch hub, and the fan will not slip, but drive at pulley rpm... WHATEVER that rpm may be until the air passing through is sufficiently cool enough to disengage the spring clutch.

Then there is motion. An interesting phenomenon known as passive cooling occurs when the velocity of ambient temperature air flows over a surface at a certain speed and it begins to cool that surface. There is a lot of science in the actual thermal efficiency and surface textures etc, but the same applies to a radiator and a vehicle.

Provided your radiator grille is not significantly obstructed by driving lights or bullbar tubes or braces or a winch, then you will have a relatively efficient flow through your radiator once you hit about 50km/h. Above that the efficiency increases until you reach about 120km/h, after which it does seem to roll off a little, but again, this is dependent on aerodynamics and how hard you are pushing the accelerator. High rpm and high speed CAN be a problem for cooling. Backing off that little bit and maintaining a good speed but a reduced rpm, will make things far more efficient - especially if the radiator is not operating efficiently.

If you're in low range, your heating issue will be compounded. high rpm and low speed is a recipe for engine bay heat and heat soak. I'll extrapolate on heat soak in a bit. But for now, just be aware that the worst conditions for causing a heat related issue are high rpm low speed.

5. HVAC, pusher fans, oil coolers mounted in front of radiator affect the cooling system efficiency in quite a significant way (negative).

If you have a blocked or corroding HVAC condensor, or the pusher fans aren't working or you have oil coolers sitting in front of the condensor which is in front of the radiator, then how do you think the cooling system performance will be affected?
Make sure you have a clean, clear unobstructed path through your hvac condensor, that your heat exchangers are clean and free from mud, grass, sticks and dust. a dirty core is an inefficient core.

Now it is time to mention heat soak.
when the cooling systems efficiency is affected, then there will be a point where the cooling system cannot remove enough heat before the combustion process creates more and adds to the latent heat already in the system. This is also called a thermal arrest. As the combustion process continues, there is more heat going in, than can be removed by the cooling system, and that curve is exponential... in the wrong direction. Once heat soak or the thermal arrest level has been exceeded by even the smallest amount, there is no reversing the trend and you are on your way to uncontrolled overheating.... turn the engine off and it will still add heat, and none can be removed since the fan is not moving.
Accelerate to a higher speed and it may temporarily seem like there is a temperature drop, but you just added more heat through increased load and engine rpm.... so the heat increases to more than it was, and you can't reverse that trend.

And this is exacerbated by running a hot dry burning fuel such as LPG.

There is nothing wrong with LPG as a fuel, but understanding how it burns is often overlooked.
LPG will burn 10-15ºC hotter than petrol, simply due to the fact that LPG enters as a gas and not as an atomized cool liquid into the combustion chamber.
You can leave all the other fancy claims at the door. But a rover v8 doesn't have direct injection for LPG or fuel, and as such, the ambient air temperature combined with the fuel and the combustion temperature is always going to be more for LPG than atomized petrol which cools the induction charge. Simple as that.

This is but one of the contributing factors to the issue at hand.

But, unless you have a known verifiable service record of that radiators last tank removal and core cleaning, then you simply cannot ignore it.
And a proper 4 core offset heavy duty radiator is going to kick you in the sensitive spot, if you find that your cooling system is simply not up to handling the extra heat from LPG.

A new fan and visco hub is cheap insurance, and pulling the radiator to have it properly cleaned, or replaced with a new brass core unit (longevity and reliability and serviceability as well as roadside repairable if damaged) is the way to go.

Yes, it will be an expensive job to replace the radiator. But it is also the one weak link in your cooling system that has not been fully mitigated. I suggest you start with a citric acid flush and replace your viscous hub and the fan.

You can get citric acid in bulk from most home brew suppliers (used to clean carboys) and you will need about 1.5-2kg to do a heavy-duty descale and flush depending on your cooling system volume
If the engine has never had it done before, be prepared to see a heap of very undesireable looking crud come out.. and make sure you reverse flush it for a good 10 minutes afterwards to ensure there is no residual solution left and all the junk is hosed out.

And after you have done that, use a good quality coolant in the correct mix ratio. The blue nulon concentrate is much better for alloy blocks in my experience. Has about a 10 year life in a mercedes if you're the lazy kind and neglect to service it, so can't be any worse in a rover v8 and I've noticed there is no green slime or scale left (unlike green coolants, like zerex g-05 etc). Most landrover engines I see haven't even seen the use of coolant in 20 years... and still people wonder why they have issues...

You can lead a horse to water...

But I'll leave you with this.

I had a radiator in my 1972 350SLC that had been recored in 1976 and I went to have it serviced in 2012, when they pulled the tanks off they found it was 90% blocked. It flowed water like there was no tomorrow. I wasn't convinced that the radiator even had an issue since I had reverse flushed it.
But when I was shown the old core (they made a new replacement core) I was shocked.

Sometimes, there is no way of knowing how bad a radiator is until you desolder the tanks.
Radiators the size of the units in older Mercedes and in Range Rovers are quite large (oversized for their application), and by modern standards of offset core technology, terribly inefficient, compared to new.

So if you do have the opportunity to re-core your unit, go with the all-brass 4 row heavy duty core. Especially since you are running LPG. Yes it's stupidly expensive (mine was almost $1600) but I'll never have to touch it again, and it is serviceable...
If you always use coolant, and service your cooling system correctly (every 2 years) then it should never need pulling apart and cleaning ever again.