Dk2685

Hello,

I have a 1989 3vze Pickup with a couple interesting issues. For starters, the truck idles very high; around 1700-2000 rpm is pretty common at startup and it never goes below 1200.

Also, I am periodically burning coolant but I can let it idle in my driveway for a while without any smoke and the truck runs on the low end of the heat spectrum. My theory is that the coolant passageway in the throttle body is blocked, from what I have read this is a pretty common issue resulting in high idle. Would this blockage lead to the burnt coolant in exhaust? The truck idles evenly without any skips or misses though I recently did a compression test which found low compression in cylinders 2 and 4. It has been through some overheating moments as i recently patched up a massive oil leak at the rear main seal and, unfortunatley previously drove without enough oil more than once resulting in engine shut off due to overheating 😬. (I also recently pulled the spark plugs and they were quite burnt 😬😬&#128556

I want to clean out or replace the throttle body but it is seized to the intake plenum and no amount of force I'm comfortable with will do the job to break it free. The idle screw is also completely seized and the boot for the dashpot is hardened and cracked.

My real question is: Is there a definitive way to diagnose a head gasket failure or is it possible just cleaning or replacing the throttle body/plenum would solve my issue? I have never replaced a head gasket but the challenge sounds kinda exciting and would love to add head gasket work to my list of skills. Excitement aside, I just finished the rear main seal job which was a pain in the ass and I kinda just want my truck to run without any major work for a while!

Thanks in advance,
DK

DallasTX

I am far, far from an expert, but here are my thoughts for your consideration. My 3vze had the same symptoms as you stated. I was slowly losing coolant, has some white cloud at the exhaust, but never had other signs of a blown gasket such as milky oil. I suspected a blown gasket, but was hoping for a different outcome, so wanted to check for other sources of coolant leaks first.

From other posts in this forum, it appears is is possible to get coolant into the throttle body if the valve ruptures in the coolant passage. There were no tell tales in the throttle body of coolant (ie. any evidence of red stains, etc), but I removed the cover to look inside. Mine was fine. If it had been ruptured, I did not see any way to repair it and I could not find any threads on repairing it, if it had been leaking I presume the only fix is a new throttle body.

Of course, also check the carpet near the heater core in case it is leaking and other hoses around the engine bay. I borrowed a radiator pressure test kit from O'Reilly's and pressured up the radiator to FSM test pressure....do not recall the amount, but around 13 lbs I think. If you cannot find, let me know and I will look it up for you. My pressure dropped, but then I saw coolant leaking out of the heater control valve, so while I definitely had a leak, I was not able to say if it was the only leak without replacing that part.

I also borrowed a block test kit (you have to purchase the fluid for $7.00) and checked the radiator head space for exhaust gases. Mine tested positive for a blown gasket even though there was no evidence of oil in radiator or any noticeable bubbles. I understand some shops do a similar test with an emissions test device. Getting a positive result was not what I wanted, so tested multiple times, flushed the device with distilled water in case the previous user contaminated it with coolant, and even bought another bottle of test fluid from a different source....still same results. All my research indicates the block test is very reliable if you follow the instructions....essentially ensure you do not contaminate it with coolant.

I pulled the heads, all the while thinking I sure hope the block test kit is accurate and I did not screw up the test. A picture of my 4,5,6 head is attached. To my untrained eye (and opinion of my more experienced friend) it appears the head gasket failed on the back side of the #6. The fire ring de-laminated a bit in that area and is discolored compared to the rest of the cylinders, plus the piston top and head are cleaner than the others...I am presuming from the steam cleaning. This would result in a slow coolant leak but not contaminate the oil since since the leak was probably very small leak and getting burned off. If anybody with experience sees this post and thinks otherwise, I am certainly interested in the feedback and can provide more pictures.

BTW, if you have access to an inspection camera that will fit into the spark plug bore, you might be able to see similar observations to help in your diagnosis if you believe you have a blown gasket. This was not an option for me.

Definitely suggest you rule out other issues first. Throttle body should not be that hard to remove. Once you have the four bolts out, the only thing that would be holding it on is the paper gasket unless a previous owner used some kind of sealant. I have cleaned mine while on the truck by parking the right side of the truck on an incline so the cleaning fluid runs back out, and putting paper towels down to soak up the carb cleaner.

Good Luck. Would be interested in what you find.