Choked exhaust

[dan_7]

My PZJ70 has had overheating issues with the engine (1PZ, 5cyl) ever since I bought it 2 years back.

It overheats, the temp needle goes over the 3/4th mark, with the a/c on, in under 10 minutes,when I'm idling in traffic or accelerating hard in the hills. On several occasions, I've let the needle go all the way to red. In such conditions the engine loses power drastically and I've to pull over and let the engine cool down; there is no boiling of water in the reservoir when the engine has overheated.

However, in normal city driving without the a/c the overheating is not much of a problem.

The other problem is a thumping noise that emanates from the engine. It is especially noticeable at idle and it's frequency also increases as the engine builds up speed but the thumping noise gets drowned out by the loud noise of the engine. Could this be back compression due to a choked exhaust?

The engine also consumes engine oil @ 1 ltr per 1000 km in the summer with the a/c on and when the engine runs hot but otherwise does not consume any engine oil. However the exhaust smoke is clean. Every month or so I have to replenish the radiator with about a liter of water. There is also a mild leakage in the cooling system when I did a pressurization test.

There is no obvious leakage of either water or engine oil. The engine compression is around 31kg/cm3 across all cylinders; the tolerable range being 27-37kg/cm3.

To remedy the problem I've replaced the radiator with a new genuine Toyota; change the themostat, examined the head and water pump; adjusted valve clearences; rebuilt the injection pump but to no avail.

I thought all there was left to do was replace the head but someone told me that the exhaust could be choked. It's a 20 yr old vehicle and I'd read somewhere that the silencer on these early models were also extremely restrictive.

My mechanic tells me that he'd have to cut open the silencer box to check for chokage. Isn't there a less painful way to confirm a restrictive exhaust and should I be looking somewhere else for the overheating problem?

[stilivn]

Where is the silencer box located. could you take the exhaust off an take it for a test drive. Will be loud but if you dont live in a crowded area with lost of cops may be an option.

[drr]

Is your engine fan working correctly? Does it lock up when the engine is hot?

[hulsty]

Dont the 1PZ's have a dual mass flywheel? Probably stuffed and that is what the thumping is.

Checked fan clutch? my old 3F behaved like that when the fan clutch was dying

[dan_7]

the fan is directly driven by the engine and the dual mass flywheel was welded to make a single piece flywheel,sometime back.

In an engine such as mine can the exhaust ever be so badly choked by soot that it overheats?

[drr]

There is no viscous fan coupling???? Seems odd, or did you modify it to be solidly driven?

[dan_7]

There is no viscous fan coupling???? Seems odd, or did you modify it to be solidly driven?

solidly driven from factory. also mentioned in the repair manual.

[drr]

All Toyotas of that vintage with an engine driven fan use a viscous coupling (the finned aluminium bit between fan and water pump), and they do fail every now and again. See link below...

http://www.toyodiy.com/parts/p_G_1992_T ... _1601.html" onclick="window.open(this.href);return false;

If you are convinced that it is a loose baffle in the exhaust, just unbolt it before the first muffler and take it for a spin, at night, with no cops around. It shouldn't be too loud.
To me, it sounds like blocked radiator(internal or external blockage) or a viscous fan coupling.

[dan_7]

All Toyotas of that vintage with an engine driven fan use a viscous coupling (the finned aluminium bit between fan and water pump), and they do fail every now and again. See link below...

http://www.toyodiy.com/parts/p_G_1992_T ... _1601.html" onclick="window.open(this.href);return false;

If you are convinced that it is a loose baffle in the exhaust, just unbolt it before the first muffler and take it for a spin, at night, with no cops around. It shouldn't be too loud.
To me, it sounds like blocked radiator(internal or external blockage) or a viscous fan coupling.

If you have a look at the repair manual there are 2 options for engines: with or wihtout the viscous fan coupling. Mine is driven directly.

Today, the silencer box was opened up but the internals were clean. We also dialled down the fuel on the pump but it's still overheating with the a/c on when the vehicle is idle.

Next week I'll have the water pump changed and then maybe I should have the head replaced.

Anything else I could do?

[clayhook]

might sounds silly and obvious but be sure to check your thermostat .couldn't hurt to replace it anyhow i suppose

[dan_7]

might sounds silly and obvious but be sure to check your thermostat .couldn't hurt to replace it anyhow i suppose

it was done sometime back.

[Kitika]

Do you get any bubbles coming through the radiator when its warmed up and running? I reckon your head is cracked as its not normal to be using coolant. How regulary do you service it and are you using the right oil for the hotter climate? Could be excess soot clogging everything up too in the motor if it hasn't been serviced properly and there is a product that can clean it out for about $100.

[BadMav]

might sounds silly and obvious but be sure to check your thermostat .couldn't hurt to replace it anyhow i suppose

it was done sometime back.

Doesn't mean it's still working though. I would check it anyway. Take it out and drop it in a pot of water and heat it on the stove (not to the boil) and it should slowly open up if it is working properly. You could even go as far as checking the opening temp with a thermometer when you do it.

[dan_7]

might sounds silly and obvious but be sure to check your thermostat .couldn't hurt to replace it anyhow i suppose

it was done sometime back.

Doesn't mean it's still working though. I would check it anyway. Take it out and drop it in a pot of water and heat it on the stove (not to the boil) and it should slowly open up if it is working properly. You could even go as far as checking the opening temp with a thermometer when you do it.

I'll recheck the thermostat when I have the water pump done but I doubt that is the problem. I only replaced the thermostat about a year back with a genuine Toyota.

The coolant reservoir doesn't boil so could it anything apart from a head gasket or head crack issue?

[dan_7]

done the thermostat and water pump. Seemed ok

I'm going to remove and inspect the head and gasket.