Filters disappear after the request

I have this selects that the user can filter his search:

They are doing what they are suppose to do. But after the submit, these values disappear from the selects.

The question is: How can I keep these filters inserted by the user after he submitted?

Here is my code:

<%= form_tag filter_vehicles_path, method: 'get', id: 'form_filter_vehicles'  do %>
    <h4><strong>

      <span>Fabricante</span>
      <%= collection_select :manufacturer, :manufacturer_id, Manufacturer.joins(:vehicles).uniq, :id, :name, {include_blank: true}, {class: "manufacturer_dropdown"} %>

      <span>Modelo</span>
      <%= grouped_collection_select :model, :model_id, Manufacturer.order(:name), :models, :name,  :id, :name, {include_blank: true}, {class: "model_dropdown", data: {models: @models}} %>

      <span>Preço</span>
      <%= select_tag :price_start, options_for_select([price(250), price(500), price(1000), price(2000), price(3000), price(4000), price(5000), price(6000), price(7000), price(8000), price(9000),price(10000), price(12000), price(14000), price(16000), price(18000), price(20000), price(22000), price(24000), price(26000), price(28000), price(30000), price(32000), price(34000), price(36000), price(38000), price(40000), price(50000), price(60000), price(70000), price(80000), price(90000), price(100000), price(150000), price(200000)]), include_blank: true, class:"select2PriceFrom" %>

      <%= select_tag :price_ending, options_for_select([price(250), price(500), price(1000), price(2000), price(3000), price(4000), price(5000), price(6000), price(7000), price(8000), price(9000),price(10000), price(12000), price(14000), price(16000), price(18000), price(20000), price(22000), price(24000), price(26000), price(28000), price(30000), price(32000), price(34000), price(36000), price(38000), price(40000), price(50000), price(60000), price(70000), price(80000), price(90000), price(100000), price(150000), price(200000)]), include_blank: true, class:"select2PriceTo" %>

      <span>Ano</span>
      <%= select_tag :year_start, options_for_select((1990..Date.today.year).to_a.reverse + ["1980", "1970", "1960", "1950", "1940", "1930", "1920", "1910", "1900"]), {include_blank: true, maxlength: 4, class:"select2YearFrom"} %>
      <%= select_tag :year_ending, options_for_select((1990..Date.today.year).to_a.reverse + ["1980", "1970", "1960", "1950", "1940", "1930", "1920", "1910", "1900"]), {include_blank: true, maxlength: 4, class:"select2YearTo"} %>

      <span>Quilómetros</span>

      <%= select_tag :kms_start, options_for_select([ kms(5000), kms(10000), kms(15000), kms(20000), kms(25000), kms(30000), kms(35000), kms(40000), kms(45000), kms(50000), kms(75000), kms(100000), kms(125000), kms(150000), kms(175000), kms(200000), kms(225000), kms(250000), kms(275000), kms(300000), kms(350000), kms(400000), kms(500000)]), include_blank: true, class:"select2KmFrom" %>

      <%= select_tag :kms_ending, options_for_select([ kms(5000), kms(10000), kms(15000), kms(20000), kms(25000), kms(30000), kms(35000), kms(40000), kms(45000), kms(50000), kms(75000), kms(100000), kms(125000), kms(150000), kms(175000), kms(200000), kms(225000), kms(250000), kms(275000), kms(300000), kms(350000), kms(400000), kms(500000)]), include_blank: true, class:"select2KmTo" %>

      <%= submit_tag "Pesquisar" %>
    </strong></h4>
  <% end %>

BTW I'm using the Select2.js library.

Thank you in advance!

add to your inputs the selected one on your html, sending the params that comes in the request. like this

selected: params[:param_name]

so you add them to every input, like this

<%= select_tag :price_start, options_for_select([price(250), price(500), price(1000), price(2000), price(3000), price(4000), price(5000), price(6000), price(7000), price(8000), price(9000),price(10000), price(12000), price(14000), price(16000), price(18000), price(20000), price(22000), price(24000), price(26000), price(28000), price(30000), price(32000), price(34000), price(36000), price(38000), price(40000), price(50000), price(60000), price(70000), price(80000), price(90000), price(100000), price(150000), price(200000)]), include_blank: true, class:"select2PriceFrom", selected: params[:price_start] %>

<%= select_tag :price_ending, options_for_select([price(250), price(500), price(1000), price(2000), price(3000), price(4000), price(5000), price(6000), price(7000), price(8000), price(9000),price(10000), price(12000), price(14000), price(16000), price(18000), price(20000), price(22000), price(24000), price(26000), price(28000), price(30000), price(32000), price(34000), price(36000), price(38000), price(40000), price(50000), price(60000), price(70000), price(80000), price(90000), price(100000), price(150000), price(200000)]), include_blank: true, class:"select2PriceTo", selected: params[:price_ending] %>