My tired 94 LE AWD Prev non-SC with HG and likely other overheating complications.

Hello forum,

I have a 94 LE AWD non-supercharged Prev, 256500 miles.

The head-gasket had been going since the vehicle had around 210000 miles. Also, At times bit sluggish to start when cold - ten to thirty seconds - until warm enough to support normal combustion and likely a bit of moisture in one cylinder - I presume.

The big disaster was a failed thermastat deep in remote Idaho mountains 236500 in summer 2011. Car got hot. I removed thermostat to get it out and the car ran fine. I put a new thermostat back in when back in civilization. But more head gasket deterioration led to the rest of the story.

The head gasket failed badly at around 237400 miles later in summer 2011, so badly that I hydrostatically locked it up three times. After the third time, I used Thermagasket, started the car dry, added water on the fly and then Thermagasket and followed the instructions. Needless to say, the product worked remarkably. Now the vehicle has 256600 miles.

Ran pretty well for about 14000 miles with care and not charging around too much.

About 5000 miles ago, the vehicle would have a hard time staying cool without running the interior heater and fan on high and especially with a grade.

After eight fresh doses of Thermagasket as preventative medicine since summer of 2011, my Previa now presents with trending toward over-heating after about thirty to forty minutes of driving, a little faster at highway speeds of course. Still, in cooler weather, with a headwind, I can drive at 60mph for four hours or more as long as there isn't much grade and I keep the engine temperature nominal while using the interior heater on full-blast. Last week, I drove from Grants Pass OR to Boise ID and only stopped once before Bend OR. On leg from Bend to Boise, I drove non-stop, mostly at 55-60mph. Hwy leg Ontario OR to Boise ID, had to slow down to 50mph as strong tailwind and still ran on warm side.

I've now seen a number of Prev motor images with cracked cylinders and blown gaskets. Most likely, if you took the head off, my motor would be a contestant in the preliminary image contest and would be a most blown head-gasket finalist.

To specifics.

Thermostat is in and new.
Overflow container and cap good.
Hoses original as far as I know.
Plugs and wires two years old.
Fan-clutch is eight months old.
Radiator flow tested last fall and nominal.
Water pump new.
Run thermagasket solution full-time.
Gas mileage good. 21 to 24 hwy.
Idles fine.
Does not lose fluid if operated in normal range.
Loses about a half a cup every hour if running on hot side.

Does not blow excessive moisture not visible as when gasket was head-gasket was really bad upon start, though holding a hand at tailpipe detects moisture. I know that water is a byproduct of normal combustion. Less moisture on hand after motor is warm.

Still slightly sluggish to start as one cylinder (a presumption) seems like it takes ten to thirty seconds to be warm enough for normal for normal combustion, but after that runs smoothly, as like a couple of years ago. When warm, starts right up.

After it gets to normal and trends towards hot, after thirty minutes or more of driving, a little quicker at hwy speeds, with very slight accelerations, it can knock once here and there, I just change the engine rpm and that alleviates the knocking. I'll even take off over-drive to increase rpms on slight declines using cruise to avoid the knocking. This is a relatively new symptom in last month.

The things I can do myself are:
1) Replace the main hoses, they might be a bit soft, especially lower but it's hard to say. They feel OK when cold and I notice no dis-figuration on forward hoses when warm or on warm side of normal. How likely is overheating from bad main hoses?

2) Replace the return hose from overflow container, as saw this fix mentioned in another forum.

3) Replace radiator (aftermarket) just because I don't know what else to do.

4) Add an additive like BG44 K if contaminants are messing with valve operations, the knocking, incomplete combustion - though I know occasion knock is most likely from heat in a cylinder (a presumption).


Most likely

1) Get a new house, as for seven months of the year, the Previa is my home.

Possible

2) Put in a used Japanese motor. How much might I expect to pay installed? Of course this solution inherently involves the overall value of a twenty year old vehicle.

Remote

1) Get a custom radiator. As I understand it, the Prev comes with one row. There might be enough room to add a second row if the fan cowling was modified.


Specific questions

1) Can a damaged, warn or sticky valve cause the overheating in conjunction with a presumed head-gasket issue as described? Hence the idea of using a treatment like BG44 K.

2) Does anyone have a referral in the Boise area.

3) Any other thoughts?


I do not have the experience to do engine work.


Thank you all in advance for your thoughtful responses.

Chuck

Hi & welcome to the forum :wave2:. Based on what you said I'd say the current engine has gone through hell. Perhaps you may be able to squeeze a little more life out of it, but short of a complete rebuild I'd consider it toast. If you have the ability to swap in a used engine yourself, then that's what I'd recommend. If not I'd probably start looking for another vehicle.

The reason I say that is strictly due to cost of repair vs market value. Used Japanese engines can be found for as low as $500-$600 but unless you're lucky enough to find one in your area you can expect to pay around $200 shipping. If you find one locally, odds are you'll need to pay around $800. Price of installation will vary from place to place, but considering the configuration of the Previa, I'm guessing most reputable shops would want in the neighborhood of $1,500 to swap. Then there's always the possibility of complications. Unless the shop is familiar with the peculiarities of the Previa it's likely they will damage the SADS or other parts during the swap. Of course this type damage will usually be presented as "while we were swapping the engine we noticed that you also need one of these". Problems with the used Japanese engines are not extremely common, but what if there's a knock or other serious issue after the swap? I'm sure the seller would likely refund or exchange, but who's going to pay for the 2nd install?

Another consideration is all the junk you've been circulating in your cooling system. Although these additives may work "short term miracles" they also fowl things up. "Head-gasket-in-a-can" (as I like to call them) can make your thermostat stick (which I'm thinking is happening now), plug up radiator cores, heater cores, and other engine passages. I would not want to reuse any of your current cooling system parts again without a thorough professional cleaning. IMO, considering the market value of other similar vehicles in decent condition, unless you have the skills & means to swap an engine yourself I would probably opt for finding another vehicle. Tim

An update to my Prev story.

I made the decision to replace the bottom main water hose Radiator to pipe) and the main hose leaving the block,as upon inspection, while vehicle was hot, both were perceivable (to the naked eye) as larger in diameter than the other two hoses ( the large top hose to the radiator, and the lower return hose (pipe to thermostat/water-pump). I did not measure with calipers.

The new return hose from radiator to pipe has less volume than the original as a small hose bend has been omitted.

I drained the system and and captured the Thermagastet solution to reuse.

As you recall I had the radiator evaluated last fall for I presume leaks, volume, and ambient flow rate) which was reported to me a nominal by the radiator guy I used. His evaluation pointed me away at looking more closely at the performance of the radiator.

Upon taking the dealing with the hoses yesterday and using genuine Toyota hoses, I rigged up a back flush to my existing radiator with a garden hose with good pressure and a capture tank and proceeded to blow out a couple of chunks of what I think is scale and some debris from failed Thermagasket - meaning what I think was Thermagasket that at some point had contributed to helping with my head gasket issue but had since blown out. The debris was much smaller in size than the scale debris.

I then made the decision to replace the radiator as my logic suggested that if indeed the blown debris from the radiator was scale, there might be much more inside, and the cost/benefit $140 to replace the radiator was worth it.

So I took out the old drained radiator. Then I laid the new radiator on the ground and filled it with about a half gallon of distilled water, eight cups. I then proceeded to empty the contents into a container and pour that into the old radiator. The old radiator accepted only five cups! That's a 37.5% reduction in volume between old and new!

I have re-assembled and have put the Prev through an hour test of highway speed driving and city driving. The vehicle operating temperature remained at normal throughout the period and I did not have to use the heater with fan on full.

I am cautiously optimistic. :dance2:That would be Woo Hoo!

Pictures and measurements forthcoming as well as more observations and my conclusions.

The first conclusion that comes to mind is that the guy that checked my old radiator and reported that it's performance was nominal may not have done the full job if any evaluation at all. I will never know. I am adverse to dis anyone but my observable data tells another story.

I'll cross my fingers for you too :wnk:.

Today, 1.5 hours of stop-and-go city driving. Outside air temperature 93F. Not a hint of over-heating.:thmbup: