LS430 2001: Radiator - oil cooler inputs for newbie

ThePerfectionOfLexus · June 25, 2023

Hi there

Newbie here from Denmark.
I’ve been a BMW enthusiast for many years, and have lately sold my beloved 7 series e38.
I simply got tired of the harsh ride, and decided to switch to Lexus.
I got interested in a currently for sale pre-facelift LS430 2001 model with 143k miles.
I’ve been reading up a lot on the LS430, which was the primary cause for choosing this specific model, as I believe it will serve my needs. I want a nice, soft and quiet ride for relaxing cruising.

I’ve attached some images of the beauty.

Some details:
I’ll be the third owner.
Documented service history
A very small portion of the lower passenger side window has delamination. According to the owner, this started several years ago and hasn’t gotten worse. So I hope it stays this way.
It’s not an Ultra Luxury, but it has dual pane windows, air suspension, navigation, and Mark Levinson sound system.

Does it make it Custom Luxury, don’t know for sure?

Anyway, I might need some inputs, since I’m completely new to Lexus.
I’ve been reading up on some weaknesses, and there seems to be one critical part, that bothers me.

According to many online sources/threads, these models tend to have major issues with the radiator, causing the coolant to leak into the gearbox, which results in a damaged gearbox.

Now, I’m used to do DIY on all my cars, so replacing a radiator won’t be a big deal.
So far, I’ve found several threads, where owners have installed an external oil cooler that eliminates the problem.
Others have replaced the stock radiator only, which already has the oil cooler inside. This seems to be a better thing to do in my eyes, since the radiator itself could be due for replacement anyway.

But I’m trying to understand, what is the actual cause of a leaking coolant into the gearbox situation?
Is the correct approach, to make sure to replace the whole radiator in time and how often to be specific, or simply just install an external oil cooler to eliminate the problem?

Rgds,

Mario

steve2006 · June 25, 2023

Hello Mario and welcome to the LOC.

It looks like a very good example that you have purchased.

I’ve never had the opportunity to examine a failed radiator/cooler to determine the exact failure cause so can only surmise it is either down to internal corrosion of the transmission cooler or fractures of the pipe work due to constant heating and cooling.

I would also suggest that the fluid mixing occurs when the engine is switched off so no hydraulic pressure but coolant pressure would remain higher until cooled down allowing engine coolant to flow into the transmission cooler.

When it comes to replacements the easiest method is a direct like for like replacement with a decent quality aftermarket unit or as you mention fitting a new coolant radiator and an external transmission cooler kit, the latter I feel being an improvement over the OEM combined set up.

From what I can gather from previous failures it seems to happen between 8-10 years so for preventative maintenance I would stick to these figures for service life.

Basically if the radiator is still the original do it now as a £200.00 part is certainly better than the cost of a replacement transmission and the labour costs involved.

Replacement fluids should of course be OEM Toyota only.

ThePerfectionOfLexus · June 25, 2023

27 minutes ago, steve2006 said:

Hello Mario and welcome to the LOC.

I’ve never had the opportunity to examine a failed radiator/cooler to determine the exact failure cause so can only surmise it is either down to internal corrosion of the transmission cooler or fractures of the pipe work due to constant heating and cooling.

I would also suggest that the fluid mixing occurs when the engine is switched off so no hydraulic pressure but coolant pressure would remain higher until cooled down allowing engine coolant to flow into the transmission cooler.

When it comes to replacements the easiest method is a direct like for like replacement with a decent quality aftermarket unit or as you mention fitting a new coolant radiator and an external transmission cooler kit, the latter I feel being an improvement over the OEM combined set up.

From what I can gather from previous failures it seems to happen between 8-10 years so for preventative maintenance I would stick to these figures for service life.

Basically if the radiator is still the original do it now as a £200.00 part is certainly better than the cost of a replacement transmission and the labour costs involved.

Replacement fluids should of course be OEM Toyota only.

Thanks Steve.
The idea of installing an external transmission cooler kit sounds fine to me however, I believe there must be a reason, why Lexus has chosen the setup with the transmission cooler inside the radiator itself.
Perhaps to heat up the tranny oil faster, don't know?

In that case, I'm fine with replacing the stock radiator every 6-7 years, to be on the safe side.
The radiator itself might need a replacement anyway.

steve2006 · June 25, 2023

It could well be the reason, I know the Aisin transmissions have a fluid temperature sensor fitted which via the ECU prevents shifting to top gear until a specified fluid temperature has been reached. Engine coolant would certainly help achieve the required temperature quicker.

ColinBarber · June 25, 2023

1 hour ago, ThePerfectionOfLexus said:

I believe there must be a reason, why Lexus has chosen the setup with the transmission cooler inside the radiator itself.
Perhaps to heat up the tranny oil faster, don't know?

Yes, faster heat up to operating temperature.

Malc1 · June 25, 2023

Mario, she looks a nice car indeed and welcome to the LOC

in addition to the advice of these two gurus I'd simply suggest that various members here have bought the incorrect radiator . the set-up on replacements sold aren't always quite right . so just take extreme care with which one you buy

Good Luck

Malc

ThePerfectionOfLexus · June 25, 2023

2 hours ago, ColinBarber said:

Yes, faster heat up to operating temperature.

Then I would prefer to replace the stock radiator and keep it in good shape, instead of the external transmission cooler kit.
I don't quite see the benefit of the latter, since the radiator might need a replacement anyway after approx. 7 years, and this would include the internal transmission cooler as well.

Am I missing something here?

1 hour ago, Malc1 said:

Mario, she looks a nice car indeed and welcome to the LOC

in addition to the advice of these two gurus I'd simply suggest that various members here have bought the incorrect radiator . the set-up on replacements sold aren't always quite right . so just take extreme care with which one you buy

Good Luck

Malc

Thanks Malc, will do.
Can an incorrect radiator, be responsible for some of the causes of a leaking coolant into the gearbox situation?

ColinBarber · June 25, 2023

53 minutes ago, ThePerfectionOfLexus said:

Am I missing something here?

No, other than a radiator would normally last longer than 7 years. The failure of the oil cooler could occur long before the rad itself needs replacing.

Provided you get an eye on corrosion at the oil pipe connections and replace the radiator before it needs it then that's the best you can do to avoid the problem.

56 minutes ago, ThePerfectionOfLexus said:

Can an incorrect radiator, be responsible for some of the causes of a leaking coolant into the gearbox situation?

That isn't the cause - the factory fitted radiator/oil coolers fail.

Tulpen · June 25, 2023

I had my radiator replaced after 100,000 miles/10 years as a precaution, having read of the problem from other members on the forum. The mechanic told me that there were signs of stress at the oil pipe connections to the oil cooler. The problem seems to be one of dissimilar metals (I can never remember if that is called electrolytic action or galvanic action - it's a long time since my engineering studies) but it definitely occurs. As Steve says, it's better to spend a few hundred pounds now than thousands later on a replacement gearbox.

The idea of combining the oil cooler and water radiator was, probably, made as a cost saving project. I understand that it was common throughout the Toyota/Lexus range for some time.

runsgrateasanut · June 25, 2023

Been trying to remember the name of the particular Radiator that caused these problems and was also used by Mercedes. My W140 Tran inlet pipe literally rusted off just as I turned a corner outside my house. I was lucky in that the Car just abut made it to my drive and I replaced the Rad. Think it was a name beginning with "B" but can't find any link to it. My LS400 still has the original Toyota Rad although I have a new Nissens replacement bought eight years ago for £40 which I've not put in as Members say the LS 400 original (to Mk 2) never fail. Perhaps after thirty years I should swap it out. Nissens is a good brand and it will be one less thing in my parts department !

ThePerfectionOfLexus · June 25, 2023

2 hours ago, ColinBarber said:

No, other than a radiator would normally last longer than 7 years. The failure of the oil cooler could occur long before the rad itself needs replacing.

Provided you get an eye on corrosion at the oil pipe connections and replace the radiator before it needs it then that's the best you can do to avoid the problem.

That isn't the cause - the factory fitted radiator/oil coolers fail.

1 hour ago, Tulpen said:

I had my radiator replaced after 100,000 miles/10 years as a precaution, having read of the problem from other members on the forum. The mechanic told me that there were signs of stress at the oil pipe connections to the oil cooler. The problem seems to be one of dissimilar metals (I can never remember if that is called electrolytic action or galvanic action - it's a long time since my engineering studies) but it definitely occurs. As Steve says, it's better to spend a few hundred pounds now than thousands later on a replacement gearbox.

The idea of combining the oil cooler and water radiator was, probably, made as a cost saving project. I understand that it was common throughout the Toyota/Lexus range for some time.

18 minutes ago, runsgrateasanut said:

Been trying to remember the name of the particular Radiator that caused these problems and was also used by Mercedes. My W140 Tran inlet pipe literally rusted off just as I turned a corner outside my house. I was lucky in that the Car just abut made it to my drive and I replaced the Rad. Think it was a name beginning with "B" but can't find any link to it. My LS400 still has the original Toyota Rad although I have a new Nissens replacement bought eight years ago for £40 which I've not put in as Members say the LS 400 original (to Mk 2) never fail. Perhaps after thirty years I should swap it out. Nissens is a good brand and it will be one less thing in my parts department !

Thanks for all the input guys, really appreciate it.
I came across this interesting thread, and posts from "The-Acre":

https://www.lexusownersclub.co.uk/forum/topic/115946-ls430-transmission-failure-total-fluid-loss/?page=2#comment-1052780

He has replaced his radiator as a precaution, and seems to point out, that the issue begins at the unions on the radiator themselves. To me this sounds like a gamble really. It's not guaranteed, that I will be able to see any corrosion in time on the unions, before the failure happens. Now I'm seriously more into installing an external tranny cooler, however the tranny oil won't be able to heat up properly this way during the Winters here i Denmark, so this is another concern.

ColinBarber · June 25, 2023

4 minutes ago, ThePerfectionOfLexus said:

To me this sounds like a gamble really. It's not guaranteed, that I will be able to see any corrosion in time on the unions, before the failure happens.

No you won't be able to fully see because the failure occurs on the inside - which allows coolant into the transmission fluid lines. If it were are simple as being on the outside then all you would get is a transmission leak and low fluid issues rather than a serve failure through water contamination.

All you can do is perform coolant changes as per the service schedule to minimise corrosion, keep an eye on the unions because you can see signs of corrosion there and replace the rad every 10 years as preventative maintenance.

The safest option is an external cooler.

runsgrateasanut · June 25, 2023

The parts supplier to Lexus and Merc didn't begin with a "B" but this thread confirms the name to avoid. Daresay they have changed the name now but do your research when replacing.

https://www.benzworld.org/threads/valeo-radiator-issue.1663220/

ambermarine · June 26, 2023

There is a fundamental reason why the transmission fluid is sent through the radiator on the Lexus LS400 and that is to keep the transmission fluid at its optimum operating temprature .

The car was sold internatioally across all the continents and the climate extremes are very relevant.

When the Mark 1 I owned was started up in a minus centigrade winters the gears were very sluggish and the sports change up and overdrive would not operate until the car had done a few miles.

This was because the engine operating temprature had not reached its optimum level and so niether had the transmission fluid.

So the radiator as well as cooling the fluid it heats it up to a consistent best operating temp and avoids burnt fluid and burnt clutches because the fluid is not getting where it should.

Because a transmission cooler individually placed in the system does not have this precise control ,example; constant idling in low speed traffic jams means no airflow over the heat exchanger the temp of the fluid could exceed its safe operating temp and burn.

runsgrateasanut · June 26, 2023

Slightly off topic, when I bought the new Nissens Radiator I also bought from Rock Auto two new Radiator Coolant rubber pipes. At the time I didn't think that possibly LHD Cars may have different spec of the Pipes. When I look at them they seem to be OK for the Mk2 Car alhough the Ref No' vary from ones I've seen. I've seen 165720 whereas the Gates is 22024 and the other is 16571c whereas the Gates is 20720. Does anyone know if LHD and RHD Rad connecting positions differ?

ThePerfectionOfLexus · June 26, 2023

7 hours ago, ambermarine said:

There is a fundamental reason why the transmission fluid is sent through the radiator on the Lexus LS400 and that is to keep the transmission fluid at its optimum operating temprature .

The car was sold internatioally across all the continents and the climate extremes are very relevant.

When the Mark 1 I owned was started up in a minus centigrade winters the gears were very sluggish and the sports change up and overdrive would not operate until the car had done a few miles.

This was because the engine operating temprature had not reached its optimum level and so niether had the transmission fluid.

So the radiator as well as cooling the fluid it heats it up to a consistent best operating temp and avoids burnt fluid and burnt clutches because the fluid is not getting where it should.

Because a transmission cooler individually placed in the system does not have this precise control ,example; constant idling in low speed traffic jams means no airflow over the heat exchanger the temp of the fluid could exceed its safe operating temp and burn.

I've been in contact with Paul Frost, the owner of Autotek- Lexus Spare Direct. I've read he should be very knowledgeable.
They sell an external transmission oil cooler for the LS430, which sits in front of the radiator.

According to his knowledge, the external oil cooler won't cause any issues with the transmission heating up Summer or Winter.

However, I would like to hear from some of you guys, that already have an external oil cooler, what is your experience?

ambermarine · June 26, 2023

Paul Frost is a breaker and renovator of Lexus cars parts as well as other high priced marques and I have in the past purchased parts for my cars from him, all good .

He has a vested interest in the sale of these independantly made oil coolers but to the best of my knowledge he his not a Lexus engineer .

I think the jury is out but I would not deviate from a Lexus design on a critical system such as the transmission.

ThePerfectionOfLexus · June 26, 2023

20 minutes ago, ambermarine said:

Paul Frost is a breaker and renovator of Lexus cars parts as well as other high priced marques and I have in the past purchased parts for my cars from him, all good .

He has a vested interest in the sale of these independantly made oil coolers but to the best of my knowledge he his not a Lexus engineer .

I think the jury is out but I would not deviate from a Lexus design on a critical system such as the transmission.

That's definitely something to consider, thank you for the input.
So what would be a good guaranteed preventive thing to do in my situation?
Simply replace the stock radiator with another stock every 7 years, and change the coolant every 5 years?

I would normally drive the car 4.5 - 5k miles per year, not much, and mostly short trips.

ambermarine · June 27, 2023

I believe that Lexus improved the specification for the manufacturing of the radiator in question and there have been no reports of any one either here or in the usa having to repeat the exercise.

ThePerfectionOfLexus · June 27, 2023

1 hour ago, ambermarine said:

I believe that Lexus improved the specification for the manufacturing of the radiator in question and there have been no reports of any one either here or in the usa having to repeat the exercise.

Is this guaranteed, any idea when it happened?

ambermarine · June 27, 2023

Nothing is guaranteed after the warranty period and it happened because Lexus are a company in pursuit of perfection . Lets not get carried away with ourselves here all of these scenarios are history so you have to take on board ancedotal evidence from the forums mentioned and as far as this thread goes for me the matter is now closed.

ThePerfectionOfLexus · June 30, 2023

Just an update for anyone reading this thread.
I've been in contact with my local Lexus department.
I was told, that the stock radiator has been improved and has a different part. no, compared to the old radiator. They couldn't tell exactly, what has been improved, but they're sure that the corrosion issue has been fixed.

cruisermark · July 1, 2023

On 6/26/2023 at 3:33 PM, HotSpur-Lexus said:

Dear reader, I am looking to put a classic Lexus in my garage alongside my Benz and BMW from yesteryear....came across this...(apologies if this car has been discussed here before)...what do people think?

https://www.stonecoldclassics.com/1992-lexus-ls400/

Its a 92 LS400 with 25K miles and looks very clean...but I am no expert on these cars...

On 6/26/2023 at 4:46 PM, ThePerfectionOfLexus said:

I've been in contact with Paul Frost, the owner of Autotek- Lexus Spare Direct. I've read he should be very knowledgeable.
They sell an external transmission oil cooler for the LS430, which sits in front of the radiator.

According to his knowledge, the external oil cooler won't cause any issues with the transmission heating up Summer or Winter.

However, I would like to hear from some of you guys, that already have an external oil cooler, what is your experience?

Mine has a seperate oil cooler fitted by the previous owner - I have not noticed any difference (this is my second 430) nor had any problems

The-Acre · July 3, 2023

Having fitted an external transmission cooler I can confirm that they cause no issues. My preference would be to replace the radiator, it's an easy job and gives you peace of mind. The original internal cooler doesn't corrode, I've taken two apart and they've been perfect, but as I've previously mentioned, slight corrosion causes the o rings not to seal causing coolant and fluid to mix. Get a decent brand of radiator, fit it and enjoy it!

ThePerfectionOfLexus · July 7, 2023

On 7/3/2023 at 7:59 AM, The-Acre said:

Having fitted an external transmission cooler I can confirm that they cause no issues. My preference would be to replace the radiator, it's an easy job and gives you peace of mind. The original internal cooler doesn't corrode, I've taken two apart and they've been perfect, but as I've previously mentioned, slight corrosion causes the o rings not to seal causing coolant and fluid to mix. Get a decent brand of radiator, fit it and enjoy it!

Thanks, I'll go with replacing the radiator with another stock part.
According to Lexus in my department, the issue should have been fixed by now, and the stock radiator has a different part number.
Regardless, I'll stick with replacing the coolant every 5 years, and hope to keep a good preventive maintenance this way.