Head gasket or oil cooler? (Defender 90 TD5)

Good day to you all. Been reading threads on here for some years (now on Landy number 4) but currently have an issue I can’t find a definitive answer to.

My Defender is a 2006 TD5 with 140k miles on the clock. Has been driving fine with no significant leaks or coolant loss. At the weekend I had to tow a 2.5ish ton trailer about 250 miles, and this seems to have induced what I believe is either a head gasket or oil cooler failure. Symptoms are small amount of oil in the coolant expansion tank and pressurisation in the cooling system leading to coolant loss from the expansion tank pressure cap.

My question is: I’ve got a small amount of oil in the expansion tank which suggests the leak/failure so far is quite minor. Would an oil cooler failure allow sufficient pressure in the cooling system to cause it to loose coolant? I’m thinking in theory that you would end up pressurising the cooling system to the same pressure as the crank case. But I was expecting to see more oil if it was the cooler hence thinking head gasket. Further, once I was on the motorway with my tow at the weekend the coolant loss seemed to stop (first hour of the journey was up and down some pretty steep minor roads) which suggests it’s only leaking at higher temps.

Decisions decisions before I start spending money! I may well do the oil cooler first and see if that cures it. At 140k miles head gasket could do with being done anyway.

Any thoughts or suggestions welcome.

id be looking at the head gasket,if oil cooler was pressurising the cooling system it would be full of oil,but after that you need to check system is good thermostat,rad get hot all over etc

Thanks for the reply. This is exactly what I was thinking. The oil really is minimal - a little bit of cottage cheese on the pressure cap and a light smear around the top of the expansion tank. Sump oil level doesn't appear to have dropped. I was convinced it was the head gasket until yesterday afternoon when someone said to me it must be the oil cooler!

Not a TD5 but my tdci oil cooler failed early in its life. On that the oil cooler is the same fitting as the oil filter housing. Symptoms were oil in the header tank, but no apparent increase in coolant pressure and no coolant loss. After it was fixed (under warranty, with a long list of other issues) and the coolant and oil changed, it took a long time to get rid of the oil residue from the cooling system. The oil contamination will have left small amounts of oil throughout the cooling system, engine block etc., even after flushing the system. This then gradually migrates up to the header tank where it sits as a thin film, which I periodically mopped out with rolled up kitchen roll until it was completely clear. Just be aware that after you have got your issue fixed, you may need to do that, or you might think the problem has not been fixed.

I recently had my 1999 Td5 head gasket replaced by an independent shop. I got less than 300km on the clock after the head gasket replacement and “bam” tons of oil squirting out of the coolant reservoir / under extreme pressure.

I’m not sure if I jumped to a wrong conclusion that the shop did a shoddy job, but I ordered a new AMC head and all new hardware. I removed the head yesterday, and I’m curious if I should invest the time removing the oil cooler and replacing the gaskets and “O” rings?

Also, If the oil cooler was the culprit, is it generally the body of the oil cooler itself, or the gasket where the centrifugal filter bolts to the oil cooler housing?

Looking for some input. Thanks!
Don

I had the coolant spitting out of the reservoir on my 90 TD5 2001. It was due to a failed HEADGASKET AND OR THE HED BEEN HOLED BETWEEN THE CYLINDER AND A WATER JACKET. SEE PICTURES.
To fix it i took off the head and found the holes where the coolant fluid had not been topped up with OAT coolant and water had been used. SO the cheapskate previous owners had thought it fine to skimp but it caused an expensive repair for me. I had to have another head and went for an AMC version made in Spain at £1300!!!!!!!!! Plus the fitting kits head bolts head gasket and manifold gasket set too. All in it cost me £2,000 .... It doesnt give any better power or performance at all but it no longer spits out fluid. I also added a new reservoir tank and pipe to the radiator , new radiator hoses and themostat too. There is a small 4 to 6 inch pipe behind the turbo as well and that was cracked so changed it as well.
It sounds like this is likely to be your problem but i had no oil just coolant. Could be the same failure though and maybe the same cause.
The lack of OAT coolant eat away the alloy head causing it to hole View attachment 265272 as you mView attachment 265272 ay be able to see in the pics.View attachment 265272

I’m in the process of re- assembling the AMC Head… FPR, Intake, Cam Carrier…don’t really feel like tearing out the Oil Cooler again. (Replaced with Chinese knock off / Britpart 2 years ago), but since I’m here, guess, I’m gonna refresh the “O” rings on the oil cooler, since I’m not really sure what the real cause of the oil in the coolant was.