Previa woes!

[terbennett]

My 1992 Previa was really acting funny. Yesterday morning on my way to work, my heater was barely working on my Previa. I looked at the temp gauge and it was approaching 3/4 of the way up. I revved it once on the freeway and the temperature went down. then I immediately went to a gas station and filled it with coolant and water. There was some in the reservoir and it was bubbling like crazy. Anyway, after that, the van ran fine all the way to work. After work, I started it and noticed immediately that it was running a little rough. I drove it home and as I exited the freeway, it actually ran worse than when I left work but it didn't overheat. K made it home and parked it. This morning, the van wouldn't even start. I'd turn the key and it made a loud noise but no usual starter noise or engine turning over. In fact the starter made a pop sound then there was a hiss type soundeach time I try to turn the van on. The engine doesn't turn over. I had the starter replaced back in 9/08 but I also checked my oil and coolant level and both are okay. Could it be a starter issue or a engine issue?

[Mog]

1st thing to do is to make sure the engine turns by hand. You should be able to reach down under the hood and rock the crankshaft back and forth by grabbing the a belt on each side of a pulley. Assuming the engine is free, then it's likely a bad starter or a bad connection on a battery post or the big starter wire. As for the overheating that's cured by a good rev, that's classic for a failing thermostat. The thermostat is located where the bottom hose goes into the engine. Mog

[vandyke]

good to replace the thermostat but make sure that the fan runs when it should. I had a near overheating experience and had to replace the fan clutch. If your van's temp gets too hot, immediately turn on the inside heater and open the windows, if you must continue to a safe stopping place.

[terbennett]

I found the problem. After removing the spark plugs and trying to start it, it turned out to be my headgasket. The issue was at the cylinder #4. It had hydro locked so when I removed the plug and tried to start it, liquid just shot out of it. That was odd since I never saw anything in my oil. Granted, I change my oil every 5-6 weeks due to the miles I put on the van (about 35,000 a year), but the oil always looked fine. The coolant had to be filled the day before the problem occured though. I'm now in the process of having the job done. Hopefully, my head isn't cracked too.

[Mog]

When my Previa blew the head gasket it did the same thing. It didn't hydro lock the motor but the coolant was leaking into the cylinder and then came out the exhaust. My oil was clean too. I'm curious what they quoted you for the repair. Mog

[terbennett]

I've been quoted from $850-1100- if the problem is just the headgasket. Of course, it could be a cracked head- which means more money but at least I have the N/A Previa so that is less likely.

[terbennett]

UPDATE: Turns out that the head did have a crack. It has been welded so it will be dropped off today and I should be back on the road by tomorrow evening.

[timsrv]

Oh man, I'd be really weary of a welded head. These Previas are all over in the salvage yards now & I would think you could get a head for pretty cheap. I would feel a lot better with good used head. Good luck and let us know how it holds up. Tim

[terbennett]

I was (and still kinda weary) too. However, my mechanic has a 1992 Previa that has a wleded head too. He has put almost 160,000 miles on it since the head was welded at 306,000- Yes, he has 466,000 on his van. Still, junkyards were telling me $150 and they would replace it or refund me if I had took it to be resurfaced and the shop found a crack in it. That leaves me wondering about the durability of a welded head as well. What is with the headgaskets going on these vans. Age, design or both? I have now seen the engine on one opened up and I'm wondering is the number four cylinder not getting as much coolant as the others.

[timsrv]

Well I guess it depends on the spot that's cracked and who does the welding. There's also the issue of alloy. The welding rod they use should be the exact alloy the head is made of. If they have that info, and can match it up, then the chances of success are much greater. Another potential problem is stress relief. When the head is welded it puts stress in that area. This is because surrounding material is not heated to the melting point like the rod. When it cools, the weld spot contracts more than the rest of the head. The head can be stress relieved (a process of heating the entire head), but it should be completely stripped down for that, then resurfaced and rebuilt afterward. Then there's possible porosity issues in the filled area. A good welder can minimize this, but it will always be more porous (less dense) than the rest of the head. All things considered, the odds of a long lasting repair are typically better with a good used head rather than a welded one. I'm not saying it can't be done, I'm just saying it's not as likely to be done correctly. Sometimes short-cuts hold up.......some times they don't. Don't get me wrong, I'm all for short-cuts, the game is getting the most bang for your buck in the odds department.

Of course no matter what you do there's always a chance for failure. You could spend a bundle on a brand new head from Toyota and still end up back in the same spot . As for your head gasket question, the struggle is the same with most engines that use aluminum heads on cast iron blocks. The problem here is expansion rates. Every time the engine is heated and cooled the head will expand and contract more than the block. This works the gasket back and forth until over time it gives way. Whenever a new engine is developed, potential problems like this are unknown until there's a lot of them out there with lots of miles on them. It's sort of random as many will make it to 300k without blowing a gasket (or cracking a head), yet others will have these problems at around 100k. Maintenance things like changing your antifreeze every couple of years will play a part as well. If the engine is ever allowed to overheat, then all bets are off. If the engine survives at all, the potential for future problems have just been greatly increased.

When I replaced the head gasket on my Previa I noticed Toyota had changed some things with the gasket. The new one had more steel in it, but it's placement was more to prevent external leaks. I didn't see any difference in the area between the water jacket and the cylinders. Good luck with your repair. I'm sure it will work out fine, the question is for how long . Lets hope you get at least another 200k miles out of it. Tim

[terbennett]

Thanks Tim.
Sorry for responding so late but I have the same concerns that you have. I had never even heard of someone welding the head if it's cracked. My understanding was that it will never be the same again no matter how well it's done. The van has a lot of vibration compared to how it ran before the issue was noticed. It used to run so smooth. Now there's vibration. My mechanic told me that he will check it out when I take it in on Friday. He thinks that te idle is too low. I think there's something else going on. I truns smoothly when it's in park. when it's in drive, it runs a little rough. I had the engine mounts changed two years ago so I doubt that the mounts are the problem but who knows. Just to cover my bases, I'm going to get the fuel injectors serviced, fuel filter replaced and the ditributor cap replaced eventhough I've been to two mechanics that have told me that those components are fine. The compression is good and pretty even and it has Genuine Toyota spark plug wires with Denso plugs. Still the vibration has me concerned. When I drive on the freeway and exit, I notice that the van runs smoother - not as smooth as before the head problem though- but much smoother than when I start out my commute.

[timsrv]

I don't think welding the head would cause the problem you mention. My concern with welding would be having it crack again in the same location. As for the rough running, that could be any number of things. As you are probably aware, the engine needs to be removed and a whole lot of other things need to be disassembled to replace a head gasket on a Previa. There are a multitude of possible mistakes even a good mechanic can make. There are 16 valves and 16 different shims. Getting just one mixed with another can cause an issue. Then there's vacuum lines and the possibility of mixing some up or leaving one disconnected. Since the cams and the distributor need to be removed it's also possible the timing wasn't set correctly or maybe a cam ended up a tooth off. Perhaps an injector plug was damaged or a temp sensor was left disconnected. maybe a wire or a chunk of dirt got pinched between a critical seal surface. Maybe the intake manifold gasket was damaged or the manifold didn't seal properly. Maybe a bolt, fitting, or some other component was left loose. Any and all of these things can and do happen on major projects (even to good mechanics). And these are only a few out of many (and yes, I've made most of these mistakes at one time or another myself). To make matters worse, the Previa is a bit unusual and can sometimes confuse the most seasoned techs. If I had one come in with a complaint like yours I would start with all the basics (check ignition timing, check the cam alignment marks, check valve lash, etc). I would also compare against a vacuum hose diagram and double check all the wires and connectors. If all that looks good, I would check for vacuum leaks around the intake manifold and verify all nuts, bolts, and fittings were properly tightened. Quite often it's the simple stuff that gets you. Good luck and I hope you get it figured out. Tim

[terbennett]

Tim, you are the king for a reason. My '92 just developed an oil leak. Turned out to be leaking from the distributor. Oil was leaking from the O-ring so I replaced it. After, putting the distributor back on, the van has been running smoothly. Seriously, it runs like a new van- no vibration whatsoever. I don't recall it ever running this smoothly.

[timsrv]

Oh yeah, the old leaky distributor o ring problem. I actually experienced this exact thing on one of my Previas. I thought it was a fluke, but maybe there is a tendency for this to happen with these. I'm a little surprised your mechanic didn't notice when he did the head gasket as the distributor cap must be removed as part of this job (I found mine by accident this way while doing my head gasket). Fortunately the distributor I pulled off my parts Previa had a nice dry interior, so I just swapped out the entire thing. Thanks for the nice comments and glad this story has a happy ending. Now lets hope that weld holds up. Tim