Engine lugging when accelerating

1991 Toyota 4Runner, V6 3 liter engine.

Had the neck on my radiator blow off while on the highway and engine got really hot. After the engine cooled down we (me and courtesy road assistance) put water in the radiator (with engine running). Also added two quarts of 15W-20 motor oil at that time. Was able to make it about 2 miles to the nearest garage where I had the radiator neck soldered back on. No more over heating but now the engine lugs a lot when ever I give it the gas. Worst at low rpms and almost no lugging above 3000 rpm. Queston: is my engine done for?


Please describe the “lugging.”

Overheating and two quarts low on oil is not a good thing. What made the radiator neck blow off?

The lugging is similar to what it would feel like if you were about to stall the engine. Jerky motion, poor acceleration. Perhaps a cylinder or two is not firing???

No clue why the radiator neck blew off. Maybe its seal was already cracked and things just got worse from there???

Best case senerio would be that you still have moisture in your ignition system to a worse case a blown head gasket. I would run a compression test to see if your cylinders are within 10% PSI of each other. If they are then I would suspect ignition issues.

Another minor cause would be fouled sparkplugs or bad plug wires.

May want to check fuel pressure also.

When an engine is overheated, it can damage certain sensors for the computer. One sensor that can become damaged is the coolant temp sensor. This is the sensor that tells the computer when to go from the open loop mode to the closed loop mode. If the sensor is damaged where the computer is never told to go into the closed loop mode once the engine comes up to full operating temperature, the fuel mixture will be too rich. This then will cause the engine to flood to the point where there’s no response from the throttle. And at low RPM’s the problem is even worse. But at high RPM’s the throttle is open far enough to allow enough air into the engine to mask the flooding condition.

You should find out if the coolant temp sensor for the computer was damaged when the engine overheated.


This is Auto Zone’s instructions on testing the coolant temperature sensor ($30). The wiring diagram shows it as a “water temperature sensor”. Click here http://www.autozone.com/servlet/UiBroker?ForwardPage=az/cds/en_us/0900823d/80/16/10/28/0900823d80161028.jsp. I think the “lugging” is misfire from a bad spark(s), missing fuel injection, or, low cylinder(s) compression. To check for spark, you could use a timing light, or an adjustable gap spark tester. 'noid lights are good to check for fuel injector signals. A compression gauge (or, a leak-down pressure tester) to check for enough compression to support combustion.