Engine overheating question Topic is solved

[scot850]

Posting here as there is more traction here than on the forum for the actual car, but it is a general question.

I was asked today by the owner of a Volvo why was his car overheating from the normal temperature that the needle sat at when exceeding 110kph (70 mph).

He was asking if his thermostat may be faulty and had already bought a temp sensor.

The only other things I could think of were:

1) A partially blocked/silted radiator
2) A failed waterpump if the impeller had perhaps come loose.

Then he told me his O2 sensor was reading badly when driving.

Final thing when I saw it was the muffler system is leaking near the front, probably forward of the cat.

He also mentioned the cat temp using a surface temp gauge was showing around 600C. That seems high to me. He seemed to have read that it should be nearer 300C. To be honest I have no idea what temp it should be. From reading some info on line it would appear that a cat can run way higher than this in the 800-1200F range when hot. If this is correct it sounds like his is running normally. Is this correct?

Now assuming the cat info is a bit of a red herring as a symptom, would the O2 sensor be reading incorrectly if the flexi-pipe is leaking badly. My thoughts is it probably is which is why he is getting a signal error, but worse it could be leaning out the engine under higher loads and hence the engine temp rising?

Any input and guidance appreciated.

Thanks,

Neil.

[lrock]

i don't know what it is, but logically we can deduce what it isn't. the thermostat, it's opening at normal temperature and allowing circulation, unless there's some reason to think it's closing again when a certain speed is reached, this can't be the issue.
Unless i totally misunderstand how thermostats work. I'm a cnc machinist, not a mechanic.

[lrock]

can he check for dtc's? (ignition on position, not started, hold read on the left stalk and push rear fog light button twice)
are those normal op temperatures internal or surface, surely it's much hotter inside than outside, by how much i don't know.
my

[Oro]

The thorough details are worthy, but check the thermostat. It’s ground zero for these issues.

The bi-metallic nature of the core function degrades over time, wear, and chemical degradation. An IR thermometer makes diagnosing this so easy, point it and shoot at temps to see if the thermometer is working correctly. The IR guns are so cheap right now (under $20 delivered, and that’s what I paid three years ago - they are less now), that no thermostat issue should be mis-diagnosed. But you don’t really need it, it just makes it faster.

Read the temps, at the the upper hose, the lower hose, and compare. Use your hand if you must, or $10 for a modern tool. The cat temps are immaterial for this issue. And if they are being read, it argues how the rad hose temps are NOT being read (because, presumably, the same IR gun is employed).

[jonesg]

I was asked today by the owner of a Volvo why was his car overheating from the normal temperature that the needle sat at when exceeding 110kph (70 mph).

He was asking if his thermostat may be faulty and had already bought a temp sensor.

The only other things I could think of were:

1) A partially blocked/silted radiator
2) A failed waterpump if the impeller had perhaps come loose.

Then he told me his O2 sensor was reading badly when driving.

the temp gauge is reading higher ,but unless verified , ts not known whether the engine is running hotter.
a $15 elm327 from amazon, using free Torque app on your phone, will show the actual coolant temp at 70 mph.

if the temp sensor was changed recently , unless genuine volvo ... its very likely crap.
I bought 2 that were useless, ended up reinstalling the original with 230K miles.
I traced my trouble to the coolant bottle, white dusty deposits were remnants of boiled off coolant,
tiny cracks in the plastic were the source.
loss of pressure = higher temp .

o2c sensor problem is caused by the flex pipe leak, $45 for new flex pipe, (double walled only).
drop the pipe , make a simple wooden jig to bolt it , front and rear, to the bench. Then cut the old flex out.
It can't be done in the car, its totally inaccessible.
Weld the new flex pipe in, tape the ends closed and use compressed air and soapy water to find air leaks and weld them up.
I also found numerous holes in the cat to hanger bracket welds which I ground out and welded closed.

[scot850]

Thanks to all you guys on your replies. The car is an 06 V50 T5 AWD with around 170,000 miles on it.

The car does get driven hard but the owner is trying to keep up maintenance but as a student there is limited funds. I help where I can.

All the points are valid. He has been monitoring the running info so he could tell (if I recall correctly) the O2 sensor is running rich.

The one point I had forgotten but jonesg mentioned. He has a hairline crack in his header tank at one corner. It did leak but he has noted that recently he has not been losing any coolant, but maybe he is not losing coolant but he he losing pressure.

Thanks guys. I'll let you know. I know a thermostat is the first point of repair followed by a muffler repair and I said I do not think the coolant temp sensor is the issue as the fan runs and continues to run for a while after stopping. The V50 turbo under hood temps are high!

Neil.

[MoVolvos]

Thanks to all you guys on your replies. The car is an 06 V50 T5 AWD with around 170,000 miles on it.

The car does get driven hard but the owner is trying to keep up maintenance but as a student there is limited funds. I help where I can.

All the points are valid. He has been monitoring the running info so he could tell (if I recall correctly) the O2 sensor is running rich.

The one point I had forgotten but jonesg mentioned. He has a hairline crack in his header tank at one corner. It did leak but he has noted that recently he has not been losing any coolant, but maybe he is not losing coolant but he he losing pressure.

Thanks guys. I'll let you know. I know a thermostat is the first point of repair followed by a muffler repair and I said I do not think the coolant temp sensor is the issue as the fan runs and continues to run for a while after stopping. The V50 turbo under hood temps are high!

Neil.

.
Years ago I had an intermittent problem with overheating on the 98 S70 T5. Would boil over and the pressure cap would release the pressure. Long story short, not sure why I was in there but I had to remove the thermostat housing and found no thermostat . After replacing no more overheating problem, so if the current thermostat is stuck opened it could be the issue.
.

[scot850]

A thermostat is on order from Napa as dealer has to order at a stupid price and he is heading out of town on Thursday. The option they have has the jiggle valve at least and it relatively painless at around $45 US. He plans to fit that himself and flush the cooling system.

Neil.

[scot850]

Looks like it was the thermostat. The car had been fitted with a good quality (???) PPS thermostat housing and thermostat. It is a devil to fit a V50 T5 AWD as the turbo engine has an airbox you have to remove through a hole that is too small for it!! You have to remove the 2 bolts holding the RH engine mount to the frame and use a large pipe or pry bar to force the engine rearwards to make just enough room to force the airbox out. Once that is done it is easy access to the thermostat housing.

Refilled the rad and all seems to be good for now. Owner is in monitoring mode. Today I will test the old thermostat to see if it opens fully or not.

Neil.