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[Entwood]

Some may remember that I had an overheating problem 2 years ago whilst in France that could not be replicated in UK and was eventually put under the heading "strange" ....  Just back from France again .. and the problem has returned .. but now I know a lot more about it.. and the "facts" fit with the situation 2 years ago almost exactly.

Problem only occurs under very specific circumstances :

Outside temperature above 25 degrees
Towing the van (1650kgs)
Either a short steep incline or a long steady one where the gearbox drops 2 gears and the RPM goes above 3000. (in other words .. pressing on a tad .. )

Under these circumstances the temperature will rise quite quickly and approach 100 - if no action taken it would rapidly go higher.

Backing off the throttle to 2000 rpm and accepting the much slower progress instantly stops the rise and it starts to drop back within 15 seconds. Hold the throttle at 2500 and the rise stops but the temp does not fall.

Selecting max hot on the CC will instantly help the temp drop, but once I'd worked out the RPM limits I wasn't doing this any more.

Once "over the hill" normal progress can be resumed, and with 19 degrees set on the CC... temp will settle to its normal towing level of around 87-92.

Solo and the same hills cause absolutely no problem, even when being silly and booting it hard to get the kickdown ... luckily no gendarmes around as the speeds got a tad higher than when towing !!!! 

Coolant is in excellent condition, water pump changed 10,000 ago when DLK did the cambelt, Thermostat changed 35,000 ago. No water loss at all, none added in the 2330 miles done on holiday, oil level is fine and also none added. AFAICT the fans are working correctly.

So what is it ??

I'm wondering if the rad is getting silted up/inefficient ?? It's done 120,000 and perhaps it just can't provide the "extra" cooling needed when the engine works really hard in higher temperatures.

The problem has not occurred either if France last year, or the UK in the past 2 years, simply because, I think, I have not towed up biggish hills in temps exceeding 25 degrees !!!

Any thoughts or ideas gratefully accepted

[JamesV6CDX]

Last time I saw an issue like this on an Omega - it was indeed the Rad.

Any cold spots? Maybe one of those thermal testing thingies might confirm?

[amba]

Had similar problem few years ago when we went to the Dordogne for 4 weeks.Temp that year was up in the 30,s and had problems with cars temp hitting 100 on several oxccasions when giving it some stick.

Never been a problem here since although on very hot days and getting on a bit on steep inclines temp starts to rise quicker than normal.

My money is the rad struggles to keep coolant and autofluid all cool at the same time so my plan is to give the rad a full flush and replace all the coolant every year then hopefully any crud in thin pipes of radiator will be removed.

[cem_devecioglu]

Entwood I have the same problem every summer.. so I'm not sure its a problem.. when climbing mountains (no towing but car is full) and AC open it quickly hits 100 celcius..  temp outside above 35 avg..  if I close AC or back off from accelerator it doesnt drop but dont go any further.. and last summer all changed in car headgaskets, thermostat and rad deeply cleaned with lime dissolvers..

[Lazydocker]

I've had exactly the same issues and worse (could even replicate it solo)...

Replace the rad Not worth messing about with trying to clean it out for the sake of £80 odd... Bung a new one in

[Kevin Wood]

I'm troubled by the fact that the heater affects it that much and that it's RPM dependant to such an extent. 

Also, 150kg of cast iron plus 10L of water doesn't instantly drop in temperature. Some problem with coolant flow past the temperature sensor might make it appear that way though.

Makes me wonder if the water pump cavitates at certain speeds. I know it shouldn't, but if it's a pattern part with a poor impeller design...?

IIRC you have quite a tortuous coolant route to the LPG evaporator too. Wonder if something is going on there? - bearing in mind that you need flow there from the coolant bridge before the coolant temperature sensor will respond to changes.

I have also got the temperature up to 100 when towing ("pressing on" up Wrotham hill with a 1500kg trailer tower on the back). The temperature didn't show any rapid changes, though, and took a couple of miles on the flat to settle back down to normal.

It could well be the radiator but, as I say, something doesn't ring true.

[feeutfo]

Cavitation caused by a minor blockage/restriction in the rad flow to water pump...?

[Lazydocker]

I understand the doubts... I was dubious too. But since changing my rad I haven't had it happen again

[Marks DTM Calib]

Interesting but I suspect little to worry about.

I suspect the clue is in the fact that we have high load and a sudden change in engine revs. This will give faster flow in the coolant system.

If we consider where the coolant temp sensor is (coolant bridge), its close to the rad return pipe.

So the sudden increase in flow for the same vehicle speed means the return temp of the water goes up as the coolant spends less time being cooled in the rad yet the air flow is over teh rad is unchanged.

If the rad was slightly blocked/silted then the effect would be worse.

But for me its no great issue. 

[PLANETNZ]

Nope nope and no... fit a seperate transmission oil cooler, the origional isnt keeping up. if you look at whats been said and the conditions this happens then...

[Kevin Wood]

Nope nope and no... fit a seperate transmission oil cooler, the origional isnt keeping up. if you look at whats been said and the conditions this happens then...

3.2s already have a separate transmission cooler.

Whilst it's in front of the main radiator I doubt it's large enough to affect engine cooling.

If we consider where the coolant temp sensor is (coolant bridge), its close to the rad return pipe.

So the sudden increase in flow for the same vehicle speed means the return temp of the water goes up as the coolant spends less time being cooled in the rad yet the air flow is over teh rad is unchanged.

Yep, true. Return temperature from the rad would vary wildly but I'd assumed it would have to pass right through the block, pump and heads to get to the coolant bridge. I never have truly got my head around the path the coolant takes through one of these engines, though. Guess I should take one apart one day and figure it out.

[YZ250]

<<snipped to only show relevant points>>

Problem only occurs under very specific circumstances :

Outside temperature above 25 degrees
Towing the van (1650kgs)
Either a short steep incline or a long steady one where the gearbox drops 2 gears and the RPM goes above 3000. (in other words .. pressing on a tad .............

Under these circumstances the temperature will rise quite quickly and approach 100 - .............

Solo and the same hills cause absolutely no problem, ...................

.................

I'm wondering if the rad is getting silted up/inefficient ?? It's done 120,000

If it's of any consolation, my temp gets near to 100 in the circumstances you list above but it quickly settles down to normal temp on the flat, and my car has half the mileage that yours has on it. Although I tow at the legal limit for the road I'm on, I do tend to 'give it some' going up hills so that I maintain that speed. Although the temperature is normally stable, long hills, such as Telegraph Hill near Devon, do cause a slight rise in temperature when towing in warmer weather, but as said, I do maintain the legal limit from the bottom of the hill all the way to the top.  It's fair to say that the engine is under quite a load during these situations. I'm towing around the same weight as you with my Bailey Senator on the back. Like you, I watch the temp gauge like a hawk. 

Hopefully nothing to worry about, I suppose it's a good job that we live in a cold climate. 

Regards
Alan

[PLANETNZ]

hmm, for the money id still fit a large(r) transmission cooler not matter what, factory ones no matter the make are ever designed for towing or anything other than standard.I would also service it (transmission) after towing and those problems no matter what!

[cem_devecioglu]

I understand the doubts... I was dubious too. But since changing my rad I haven't had it happen again

climbing a mountain/hill car dont have fast air flow besides the air is not cold..  I dont think these cars are designed to climb mountains with loads at a boiling temperature   in that case a more expensive cooling system would be designed for car which already has issues with mods..
 
an important hint.. I have travelled the same route alone (without loads) in hot summer where I really hammered omega without any load and over 110/120 km/hr speeds..   I witnessed the same temp increase.. so result was same.. friends bmw 530 had the same problem..

[2woody]

you're running out of cooling capacity, that's all. You might not get to fix this.

The recipe for "worst-case" cooling would be something like :-

high ambient temperature
car fitted with air-con
air-con being used
extra engine load due to uphill
auto trans in kickdown ( dropped two gears )
torque converter unlocked
low road speed.

I'd say you've ticked pretty much all of these.

To minimise the situation :-

use "econ" only on the heater - this turns off the air-con compressor, relieving the engine of 20BHP of extra load ( 10 BHP less for the cooling system to cope with ) and removing the heating effect of the air-con matrix to the radiator's input air.

use manual hold-down in the transmission, rather than letting it make up it's own mind which gear to be in. This'll allow you to get to the summit with less torque converter activity.