Defender 90 (1995) 300Tdi - Thermostat

Hello everyone,

I was hoping someone might be able to help me. Fairly new to the truck I've got and as such I've been through the Workshop manual wot I downloaded.

I recently took my truck up Newmarket way on an offroad course. Got it caked in mud.

Since I did that, the temperature gauge in the cab has been reading on the high side. When turned on it rises up slowly to half way and sits there for a bit. The longer the journey, the higher this slowly creeps. A 20 minute journey in town traffic would leave it 3/4 of the way up towards the red.

Motorway driving in excess of 60 also results in a reasonably high gauge.

I've hosed through the rad and the fins look good. You can see all the way through to the leccy fan for 99% of it.

There are no leaks as far as I can work out from the cooling system.

I've opened up the thermostat housing (shortly after shearing off a bolt, well done.) There is no thermostat in there.

I've been told this bodge is sometimes done to cope with overheating (now pretty ironic).

Firstly,

Would the absence of the thermostat result in the symptoms above?

Secondly, what the hell. If I shove a new thermostat in there, might it resolve the overheating?

Would appreciate any pointers, advice, etc.

Cheers all,
Andy

have you got air con ,300 rads are prone to fail even if looking good you have to test by feeling all over rad core to make sure its all helping to cool,thermostat would only be useful till running temp achieved,and should be fitted to let engine get there quickly ,check also viscous fan locks when hot and not just spinning,obviously wont matter on run but will be critical in traffic,if youve got aircon have you just cleaned front condensor and not rad

Hi James,

Thanks for the quick reply.

There's no air con on this one. The viscous fan was switched out for a Kenlowe leccy one. This one comes on at a particular temp but not sure it helps to cool it that much.

When the gauge reads hot, would I expect the rad to be hot or cold? Probably cold, right?

Cheers,
Andy

cold except down side with hoses on if faulty hot all over if good

Hi James,

Thanks for the reply. I put a new thermostat in. Now the gauge indicates overheating a lot quicker. Over a 10 minute drive at 30-40 it goes up into the red and beyond.

The fan does little to reduce this.

When stopped, the exchange tank is hot. The thermostat housing is hot. The radiator is stone cold in parts.

Would the 'absence' of radiator efficiency at this driving speed / length of journey lead to overheating?

If the radiator is borked, can it be revived (hose pipe in etc, rad clear) or ought it to be replaced?

Anyone any idea of how much someone (berkshirelandrover.com for example) would charge to replace it. I.e. Is it a labour-intensive job?

Thanks,
Andy

rad is very easy to change just release cowl undo 4x bolt on top frame plus oil cooler pipes 24mm/15/16 and hoses new rad £100

Did my rad yesterdy took bout an hour from bonnet up to bonnet down.

Had a bit of a fiddle getting viscous fan off otherwise probe wud of taken bout 45mins.

Sam

Are you sure you havent bought the higher temp thermostat? Mine sits between half and 3/4 (or used to till my temp sender went west, can't be arsed fixing!) and mine is the higher temp one. (87*c I think??)

i would say rad is poked mate... had the same thing happening and checked everything... also running no stat and when i eventually removed the rad (which looked ok) the core was shot.... new rad in and everything was cool... literally.... are you in berkshire, i am if you need help mate.

I bought the 88C replacement which is what the manual suggested. As there are cold parts of the radiator I wonder if that is screwed. I'm under a little time pressure to get this done so I'm toying with either flushing it out with a hose in the event that it's sludged up, or just replacing it altogether.

Seems odd that now having added the thermostat, the bloody gauge says it's overheating.

Would a non functioning intercooler cause these symptoms?

Ta,
Andy

you can test thermostat by feeoling top hose if it gets hot thermostat is open rad must be hot all over core but obviously cooling toward bottom if not and top hose hot fit new rad or new head later

Yeah, I think you must be right.

It's all come about after giving it a bit of a kicking off road.

Yep, I am in Berkshire, Reading.

Thanks James. Top hose was hot so thermostat = fine. New rad incoming then I think. Cheers for the advice.

it will overheat quicker now with the stat in as the stat is doing its' job and restricting coolant flow until op temp is reached. a sludged up intercooler could cause that problem under load but it definitely sounds to me like your rads' core is poked, flushing it will not show any prbs only clean it out and potentially waste anti freeze and time. Like i say, I had the exact same symptoms and went down all the roads of checking each component until i eventually replaced the rad, when i removed the old rad the core was rotten through but looked perfect on a cursory inspection...

Sound advice, cheers. Will attempt rad switch this week then I think.

have u got a podger or a viscous spanner? you will need one or the other when u do it bud.

A podger?

There's a Kenlowe leccy fan stuck to the back of the radiator. Lord knows where its thermostat bulb is tho. Haven't looked.

oh yeah, u said u gotta leccy fan... makes the job even easier then

Oh yes! Missed the bit about cool spots! I'd say rad too then as mentioned!

Had similar symptoms on my 90 and went for a new radiator, the old one was as rotten as a rotten thing from rottenshire, once out you could see the extent of it! It would have cooked the head if I'd carried on like that for sure. A new radiator later and the gauge now sits dead centre regardless of load, on or off the road!