Welcome to SEVERE Toyo sludge. This engine may be a disaster about to happen.
Heres what I would do without regard to brand or cost; Buy 3 or 4 bottles of Auto-RX. This is the only product that will safely clean this engine on the fly. After RX you can use a Nuetra or LC but not before as a chunk is going to come loose and ruin this engine, if it hasn't already. When I say chunk it could be very small and ruin this thing.
Manually clean as much of the top of the heads and valve covers as you can. Clean and replace the PCV valve and tubing as it has got to be blocked off with sludge. Make sure nothing is plugged in the oil journals and returns on the heads.
Change the oil add a bottle of RX and fresh filter for 250 miles, change filter and top up with oil, go another 500 miles. Change oil and filter again add another bottle of RX, run 500 miles change filter, run another 500 miles.
Change oil and filter use 3rd bottle of RX for 2000 miles.
Then I would use Redline 5w-30 and go 3000 miles and change oil and filter. Run Redline 5w-30 for 5000 mile interval and at end of that interval run another bottle of RX in the used Redline before change with a fresh filter and it should be clean.
I would stick with the Redline 5w-30 or at that point ask us here to doctor you a oil regime to eliminate this happening again.
The other alternative is to teardown the engine and manually clean but you could still damage something like a bearing or burn a piston or valve.
And honestly it may have already happened.
Call Toyota's sludge hotline and get them to help. 1 888 802 9436 tell them Terry Dyson said to call from Dyson Analysis.
If you have a coolant leak you would have noticed it by 36,000 miles by the need to add coolant. If thats what happened Toyota will not cover you.
If you choose to clean with the regimen above sample the used oil and post here for us to look at. That way you'll know if something is seriously damaged without going through the whole cleaning process.
[ June 24, 2003, 11:59 PM: Message edited by: Terry ]