[dzasta]

I hope someone here can help, I will try to be brief.
I have a Sierra with G16b
About 3 months ago I had a new radiator fitted. About a month later driving on the freeway, on a very hot day, the temp went all the way to the red zone. I turned off and into the wind and the temp came down to half and stayed there all the way up the coast, even when I had to wait for 2 light changes at Scarborough. I got back on the freeway and the temp went straight back to the red zone.
I had the thermostat changed and it made no difference. They then took out the thermostat and cut the guts out and put it back in but still runs at at least 3/4.
The fan and shroud etc are the same but I think the radiator looks much smaller than the last one.
Anyone have this problem and solved it? any ideas?

[jdk81]

Got a pic of the radiator?
Pic of the front of the car? Much stuff blocking air flow?
btw removing the thermostat sucks.

Check water levels, get it pressure tested.

How's the water pump?
Any check engine light? What do the plugs look like? Look like its running lean and hot?
How's the oil?

Possibly head gasket, hope it's not a block/head issue,

[dzasta]

I don't have pic and cant post here anyway.
There is nothing blocking airflow.
Coolant level is fine.
Mechanic says water pump and fan are both fine
No check engine light and if it was "running lean and hot" surely the temp would go up and stay up?
Oil looks fine
Thanks for your input. It looks like I am at the mercy of another mechanic.

[Gwagensteve]

What fan and shroud are you running?

[dzasta]

the fan and shroud are what came with the motor. I assume they are standard.

[Buckman]

How old is the water pump? My money is on the water pump being on its way out

[MrRocky]

Get new rad there only $100 from ebay

[alien]

when that was happening to mine it was a head gasket leak blowing into the system making it boil over. Check your overflow bottle isn't overflowing, that was one of the main signs with mine (and it didn't suck the coolant back from the overflow).

Less alarmist - do you have the plastic tray thing that goes from the bottom of the grille under the radiator? If you don't, that could be the cause, creating a vacuum and no air flow for the rad.

[shep]

Are you loosing coolant? Is it really hot or is it just the gauge saying that it is hot?

[dzasta]

I took the radiator out and it looks fine with no blockage.
checked the fan and it appears OK there is no play in the coupling.
Put the hose in the bottom hose and water pumped out the top hose with the engine running.
I have put it all back together with genuine thermostat and hope it is gonna work.

[shep]

How did you inspect the radiator for blockage? The tanks need to be removed to see if blocked.

Also would be handy if you answered the questions I asked two posts up

[Gwagensteve]

dzasta wrote:

the fan and shroud are what came with the motor. I assume they are standard.

That's a bit confusing. If you have a G16B Viscous fan that's great. You won't have a Vitara shroud as it won't fit the Sierra radiator.

If you have a (functional) G16B viscous fan and Sierra shroud you have plenty of airflow, that won't be the problem. That setup cools G16B's under all circumstances in a Sierra.

My guess is a cracked head.

Steve.

[Reubs]

Could just as easily be a blocked radiator. Just because it will flow water from a garden hose or look okay through the cap hole doesn't mean it isn't cactus.

Is it losing coolant? Cracked G16 blocks are so common odds are it's cracked.

[dzasta]

It is not using coolant. The last mechanic that looked at it said he checked the head and it OK.
In the morning the temp stays "normal" but in the arvo when it is hot the temp goes up and if I drive when it is really hot weather the temp goes to the red zone. That tells me the guage is working fine or it would show hot at any time.

[alien]

Not really - my gauge reads about 1/3rd most of the time, but on warmer days it goes up to half way. This was really concerning me so i poked an IR gun around and found it to be a minimal temp difference (cant remember exactly, but it was like 5 degrees). The gauge is NOT accurate, it's just a rough guesstimation (much like your fuel gauge)

[MrRocky]

You are overcomplicating the issue
unless you have the end tanks removed and the core rodded you wont be able to tell how blocked it is at that point you have just spent $100+ that is the cost of a new radiator.
If the thermostat is working, the shroud is factory and the fan is factory then all fingers point to blocked radiator

[jdk81]

I would have expected the coolant to be drained and replaced 3 months ago when the new radiator was installed, and I wouldnt expect a 3mth old radiator to be blocked.

I would be more interested in the motivation behind the new radiator.

[MrRocky]

New radiator fitted by shop could be an oldie with a paintjob

[MrRocky]

Mud stuck in fins ?

[pete_79]

MrRocky wrote:

Mud stuck in fins ?

Or fins flattened over by blasting it too close with the pressure cleaner?

[dtchch]

Does your heater blow hot air? If there was a blockage in the heater it would stop water circulation.

Also I wouldn't trust most mechanics, without pulling the water pump out you can't tell for sure. Could be work taking the car in to have the radiator tested.
Stop driving it if it's getting hot, you'll crack a head or block

[mazdaspater]

I once helped a mate with a falcon that overheated, new rad, new fan, new Thermostat, pressure tests good, head gasket tests good.

Pulled the pump, the fins on the impeller were corroded away to ridges, it didn't pump at anything over idle speeds. You could see flow across cap hole at idle but seemed to diminish with engine speed.

New pump fixed issue.

[dzasta]

I wish I could finish this with an answer. I have searched all over the web and very few posts end with the answer.
Where I'm at now. It doesn't use or loose coolant. The radiator is 5 months old and the thermostat is 1 week old and they are both genuine. The water pump, fan and temp gauge all appear to work and there is nothing blocking the front.
When I drive to work the temp goes to about 1/2 till close to work when I get very heavy traffic and lots of light changes and the temp goes down to 1/3. On the way home it is Ok for the first half then on the freeway the temp goes over 1/2.
I'm sure a mechanic could find the problem if I gave him an open cheque but I am just not prepared to spend that kind of money anymore.
I think I will park it in the shed till winter then sell it and do what I should have done in the first place, buy a Jeep.

[Gwagensteve]

Post a photo of the radiator and engine bay. Post a photo of the front of the car.

It's possible the system wasn't bled properly when the radiator was changed. This isn't a complex problem to solve, you just have to be methodical and persistent.

Jeeps are hardly the pinnacle of reliability.

[AckerDackerly]

Gwagensteve wrote:

Post a photo of the radiator and engine bay. Post a photo of the front of the car.

It's possible the system wasn't bled properly when the radiator was changed. This isn't a complex problem to solve, you just have to be methodical and persistent.

Jeeps are hardly the pinnacle of reliability.

What Gwagensteve said!

Following this thread to here, I believe that the water pump - as some suggested - is on it's last legs. At idle, what remains of the corroded aluminum (sp?) blades are circulating water. Once you rev the engine and hold it at speed the blades cavitate causing nothing to circulate which causes overheating.

Because of how the front of the G-series engines were designed, it is always a good idea to change the water pump every time one changes the timing belt as the pump becomes easily accessable during that task. Bonus: water pumps are cheap! If this vehicle has not had a fresh timing belt in a while, Now would be a good time to change the belt AND replace the pump. When you do, you'll probably find out why you have these problems.

The only other problem that pops into my mind would be the fan clutch, but you indicate it is good....

Finally, these are old vehicles. They need regular maintenance - just like a Jeep(tm) does. The great thing about a Sierra and a G-series engine is that they are very easy to work on. It follows that your mechanic will probably charge you more to keep a Jeep(tm) running than your Sierra...

Try to send us pics in your posts. They are often very helpful!

[Gwagensteve]

Considering the issues many of us have had bleeding the cooling system with G16b converted sierras you'd really want to rule that out first.

Then properly check fan operation. When the car is cold and the engine off the fan should feel quite "sticky" and only free up after a bit of back-and-forth turning. When the car is cold the fan should turn and roar until the car has run for a minute or so. You should also hear it roar when the temp gauge is up at all. It will be a noticeable increase in noise. These viscous fans are quite old now and it's not uncommon to have to refresh the vicious oil in them.

Steve.

[Jimny_No_Power]

You can service the fan clutch. Easier with an impact driver and the correct driver bit. I picked up some silicone oil from Toyota service dept for $19 and topped mine up. It's thicker than the factory oil which I've read can cause over cooling, but I don't think that'll be an issue in your case

Just another thought. Have you checked the ECT? They can be a real shit, I've actually had mine at 3/4 temp only to find it was a bad ECT sensor and wasn't overheating at all. Avoid the generic ebay ones, if you can't afford new go scrapyard hunting

[Buckman]

I do this stuff day in day out. Replace your water pump.

[dzasta]

There is definitely nothing wrong with the water pump. The one in it looks better than the new one I bought to replace it.
I cant post attachments here or I would post a couple of photos.

[Gwagensteve]

So what do you think the problem is? You've told us all the things it apparently isn't. What's left?